The participant and Expert were seated as in the Matching Task. Each set of cards from the Matching Task were shuffled so that they were in random order; each set was arranged in 3 rows of 4. The Expert and participant were told to work together to form "sets" of cards that shared some common characteristic (e.g., physical appearance, the jobs or territories of the creatures, or the sounds of the creatures' names). The SET task was chosen as a "targeted language game" (Brown-Schmidt and Tanenhaus, 2008; Tanenhaus and Brown-Schmidt, 2008), designed to elicit conversation regarding what each participant knew about the creatures. The Expert and participant took turns choosing two cards from their set of cards; their partner's job was to choose a card from their set of cards that would complete a set with the first two cards that were chosen. They were encouraged to choose their two cards carefully when it was their turn, so that their partner had the best chance of being able to complete a set. The Expert and participant were allowed to tell their partner what characteristic they had in mind for the set, but could not coach their partner on which specific card to use. The Expert and participant were each given one "PASS" to use if they could not complete a set, and were told the goal was to use as many cards as they could before using their PASSes. The conversations and card choices were recorded and transcribed. The transcriptions were later annotated by the experimenter, who marked each reference to a character or rune and tagged it as belonging to one of 3 categories: N, N+D, or D.

#### 2.1.6. Post-Test

#### **<IP_ADDRESS>. Expert**

In order to assess changes in the Expert's beliefs following the SET task, the final worksheet asked Experts to give a final YES/NO judgment regarding their partner's knowledge of names, and also asked about changes in their beliefs about their partner's knowledge from the game over the course of completing the two tasks, and their strategy during the SET task.

#### **<IP_ADDRESS>. Participant**

The final worksheet asked questions regarding the difficulty of the SET task and their strategies during the SET task, as well as questions about their memory for the names of the creatures and runes, how often they thought they'd used the names, and their strategy for referring to creatures or runes whose names they did not know.

### 2.2. Experiment 1 Results

#### 2.2.1. Experts' Initial Beliefs

We first assessed the Expert's initial beliefs and explored the extent to which these beliefs relate to the knowledge of their Day 2 partner. We converted the Experts' Pre-Test number-line ratings into YES/NO judgments by norming them to a value between 0 and 1, and assigning estimates below 0.5 to NO and estimates above 0.5 to YES. If the partner had answered "no" or gave an incorrect name for an item in the Pre-Test, they were coded as not knowing the name; if they answered "yes" and gave a correct name for an item, they were coded as knowing the name. Experts were correct in their Pre-Test judgments about which names their partner knew and did not know 80% of the time when they were working with the same partner as on Day 1, and 68% of the time when they were working with a different partner than on Day 1, which suggests some use of partner-specific information. **Table 2** compares the expectation of the Expert regarding whether their Day 2 partner knew a particular name with the actual knowledge of that partner, as indicated by the partner's Pre-Test responses. Incorrect judgments are bolded. Note that there does appear to be a "Curse of Knowledge" effect in the Experts' response patterns, particularly when the Expert is working with a different partner on Day 2 than on Day 1: Experts assume their partner knows a name when it is not actually known 27.6% of the time when working with the partner, and 42.7% of the time when working with a different Day 2 partner.

However, Experts' basis for their beliefs regarding partner knowledge is more likely to be the experience in the game itself on Day 1, during which their partners may have learned names that were subsequently forgotten by Day 2, and thus in **Table 3**, we present the percentages of correct and incorrect judgments about partner knowledge broken down by what their partner actually learned, rather than what they report remembering on Day 2; note the dramatic reduction in incorrect judgments about knowledge status for items that the Expert expects to be known (from 27.6 to 2% for the same partners, and from 42.7 to 11.7% for different partners).

To test whether Expert's judgements reflect parter-specific information, we modeled the accuracy (based on their partner's Day 2 Pre-Test knowledge) of Experts' Pre-Test Yes/No judgments about whether a particular item was known using a mixed effects logistic regression model with the partner's status (same as Day 1 or different) as a fixed effect, along with random effects for the partner, Expert, and item. We found a significant main effect of the partner's status, such that Experts were more likely to be accurate in their judgments about whether their partner knew a particular item if their partner was the person they had played the game with on the previous day (β = 0.82, S.E. = 0.39, p < 0.05). But when we add Game Experience (whether or not a name was learned by the partner on Day 1) to this model, the partner's Day 2 knowledge is no longer a significant predictor; instead, we find a main effect of Game Experience, such that Experts' ratings of the likelihood that their partner knows a name are significantly higher when that name was learned during Day 1 (β = 1.16, S.E. = 0.38, p < 0.01), and there is no interaction with partner status, likely due to the

TABLE 2 | Expert's Pre-Test judgments of what Day 2 Partner knows and does not know, compared to the Partner's actual knowledge (based on Pre-Test).

TABLE 3 | Expert's Pre-Test judgments of what Day 2 Partner knows and does not know, compared to the names Partner actually learned on Day 1 (Game Experience).

fact that most participants had relatively similar performance (and thus learned similar names) during Day 1. Thus, while Experts' judgments regarding the likelihood that their partner knows a name reflect partner-specific information, they are still relatively accurate for new partners, based on their implicit sense of which names were likely to have been learned during the game.

#### 2.2.2. Patterns of Referring Expression Choice during Matching Task

In order to explore whether the partner's use of referring expressions could have provided a useful cue to the Expert regarding that partner's knowledge, we annotated the transcripts from the Matching task, coding each reference to a named feature or creature as either an N, an N+D , or a D. If a creature was referred to using a description that included the feature name (e.g., "The Wug with the Bor" in reference to the creature Molgiroo, a "Wug" family creature with the "Bor" feature), this was coded as an N for the feature and a D for the creature; features could also be described rather than named, as in "The Wug with the thing that looks like a rocket," and this would be coded as a D for both the feature and the creature. Because of the nature of the matching task, participants were sometimes able to complete the task without referring to all of the creatures; these were coded as "NONE." We then recorded the final utterance type from the naive participant referring to that feature or creature (N, D or N+D). This gave us a measure of the evidence provided by the participants' utterances. **Figure 2** shows the distribution of the partners' first utterances during the Matching task for known and unknown creatures and features.

For items whose names the partner did know, according to the partner's Pre-Test, the partner used the N form 37% of the time, the N+D form 9% of the time, and the D form 48% of the time.

The vast majority of names used by the partner were for features; 81% of the partner's N uses and 53% of the partner's N+D uses were for features rather than for creatures. Note that the partners here are using the N form more often than the N+D form for the names they know; this is likely due to the fact that they are interacting with people whom they know to be Experts, and so can safely refer using only the name. Experts almost never used names during the Matching Task, which was almost certainly driven by the fact that they were playing the role of matcher rather than director.

Note that there are a small percentage of N and N+D uses by the partner for "unknown" items. In all cases where the participant used the N form for an "unknown" item, the participant initially used an incorrect form of the name (and had done so during the Pre-Test as well), and the Expert provided a correction, which the partner then proceeded to use throughout the task, as in the following example:

**Partner:** The next one has a **Rep** on it... **Expert:** Do you mean **Rab**? The half-star? **Partner:** Oh yes, sorry, **Rab**!

In sum, partners did not use names for all of the items whose names were known to them during the Matching task, but they did use some names. In choosing to use names for particular items, partners may have provided evidence to the Expert regarding their knowledge not only of that item, but of other items that should have been learned alongside it. Likewise, in deciding to use a description for an item, partners may have provided evidence to the Expert that suggested a lack of knowledge of that item's name, evidence that could be misleading if the name is actually known by the partner. Did this evidence contribute to changes in Experts' beliefs about partner knowledge? In the next section, we provide an overview of the changes in Experts' beliefs about what their partner did and did not know, and evaluate the extent to which these changes can be predicted by the evidence provided by the partner during the Matching Task.

#### 2.2.3. Changes in Experts' Beliefs at Mid-Test

In order to explore the changes in Experts' beliefs about partner knowledge and the extent to which these changes were driven by the evidence provided in the Matching Task, we first converted the Experts' likelihood estimates from the Mid-Test into YES/NO judgments in the same manner as for the Pre-Test estimates. We find that in the Mid-Test, the difference between Experts' accuracy on YES/NO judgments for same Day 2 partner vs. different Day 2 partner disappear: Experts were correct in their judgments around 79% of the time for both types of partner, meaning that Experts' accuracy for different Day 2 partners improved by 10% over their performance in the Pre-Test.

A summary of the Experts' judgment data from the Mid-Test, broken down by the items the partner did and did not actually know, is given in **Table 4**.

An examination of **Table 4** in comparison to **Table 2** reveals some interesting changes. Most striking are the improvements

TABLE 4 | Experts' Mid-Test Judgements relative to Partners' Pre-Test Memory for names.

in Experts' judgments regarding the knowledge of their partner when their partner was different on Day 2; for different partners, Experts correctly believe things to be known when they are in fact known 90.6% of the time in the Mid-Test, compared to 57.3% of the time in the Pre-Test. The "Curse of Knowledge"-type errors are reduced when working with the same partner, as well: Experts correctly believe things to be known when they are in fact known 80.7% of the time in the Mid-Test compared to 72.4% of the time in the Pre-Test.

In order to assess whether these differences reflected significant improvements in judgements from the Pre-Test to the Mid-Test, we used a mixed effects logistic regression model to predict whether the YES/NO value of the Expert's judgment was correct, with the test from which that judgment came (Pre-Test or Mid-Test) and the partner status (same Day 2 or different Day 2) as fixed effects and participant number, item name, and Expert name as random slopes and intercepts. We found a significant main effect of judgment type on accuracy, such that judgments that came from the Pre-Test were less likely to be accurate than judgments that came from the Mid-Test (β = −0.58, S.E. = 0.18, p < 0.01).

To test whether Experts' Mid-Test judgments were influenced by the evidence provided in the form of their partner's referring expression choices, we used a mixed effects multi-level regression model to predict the Expert's Mid-Test Yes/No judgment for each item, with the referring expression choice of the partner for that item (N, N+D, D, or none) as a fixed effect and participant number, item name, and Expert name as random slopes and intercepts. Experts were significantly more likely to rate an item as "known" when the partner had used the N form to refer to the item (β = 6.45, S.E. = 0.82, p < 0.0001) and also when the partner had used an N+D form (β = 3.97, S.E. = 0.86, p < 0.0001), and were significantly less likely to rate an item as "known" when the partner had used a description (β = −4.04, S.E. = 0.52, p < 0.0001).

We had hoped to test whether Experts would alter their belief about the status of one item based on the evidence provided in relation to another item. However, the patterns of referring expression choice by the partners made that impossible; there were not enough cases where a partner used a name from "later" in the game without also having used one from earlier in the game. There was one striking example, in which the Expert was working with a different partner on Day 2 than he had worked with on Day 1. This partner had made it to the end of the game on Day 1, and during the Matching Task, used names for some, but not all of the creatures she had encountered. She did, however, refer to the final creature from the Day 1 game as "King Floogelor" during the Matching Task, and the Expert reacted with surprise that she knew that name. In this particular case, the Expert dramatically increased his ratings on the Mid-Test (compared to the Pre-Test) for all items. But this was the only example of this type in the dataset. In order to ask specifically about whether the use of one name can lead to generalizations about knowledge of other names, it may be necessary to use partially-scripted games; we present one such approach in Experiment 2.

#### 2.2.4. Patterns of Referring Expression and Set Choice during SET Task

In order to explore whether these changes in beliefs about partner knowledge were reflected in the Expert's referring expression choices during the SET task, we used the same annotation and coding scheme as for the transcripts for the Matching Task, additionally coding the first utterance type from the Expert. **Figure 3** gives the distribution of utterance types (N, ND, D, and none) during the SET task for partners and for Experts, respectively.

Unlike the Matching task, Experts used many names during the SET task, restricting their use of names to those items that were actually known by their partner; this was aided by their updated beliefs regarding their partner's knowledge. Models using the Expert's Mid-Test judgments to predict the choice of the N-form in the SET task are a better fit (based on AIC) than those using the Expert's Pre-Test judgments. The connection to the evidence provided by the partner is strong: when we use the form of referring expression chosen by the partner in the Matching Task to predict the form of referring expression chosen by the Expert in the SET Task, we find that Experts are significantly more likely to use the N-form when the partner used the Nform (β = 4.94, S.E. = 0.72, p < 0.001) or the N+D form (β = 3.27, S.E. = 0.95, p < 0.001) for that item. The handful of instances in which an N form was used for an unknown-to-thepartner item occurred on the final turns of the SET game; at that point it was obvious which card remained, and so the utterance could be understood by the partner even without knowing the name.

# 2.3. Experiment 1 General Discussion

Experts' initial beliefs regarding their Day 2 partner's knowledge of names did reflect partner-specific information, as evidenced by the higher accuracy of their Pre-Test judgements when working with the same Day 2 partner as when working with a different Day 2 partner. When working with unfamiliar partners on Day 2, Experts' initial beliefs regarding those partner's knowledge was influenced by the Experts' game-playing experience, and thus still more accurate than might be expected if the Experts' had no basis for forming expectations regarding their partners' knowledge. The partner's referring expression choices during the initial referential communication task did provide useful information regarding the partner's knowledge of names, but partner did not always use the N form for names that were known. Experts were

able to use the information provided by the form of their partner's referring expressions to generate more accurate beliefs regarding their partner's knowledge of names, which was apparent both in Mid-Test and Post-Test explicit judgements, and in the form of referring expression chosen by the Expert in the final SET task.

There are limitations inherent to the design of this study. Because we used only two Experts, it is difficult to draw general conclusions about what people with expertise do when speaking to those whose knowledge only partly overlaps with their own. Another concern is that by explicitly asking the Experts to make repeated judgments about their partner's likely knowledge, we highlighted the issue of partner knowledge for the Experts in a way that typical conversation does not, and thus made that information more available and salient, which Galati and Brennan (2010) argue is a key factor for finding evidence of CGuse; over the course of the experiment, each Expert was asked to complete 16 Pre-Tests, 16 Mid-Tests, and 16 Post-Tests regarding their partners' knowledge. We can't argue that these tests did not bias the Experts toward more careful attention to their partner's knowledge state, but the results of Experiment 1 do show that it is possible for people to attend to the evidence provided by their fellow interlocutor in the form of their choice of referring expression in order to update their beliefs regarding what is and is not shared, and can use this information in deciding how to refer in subsequent conversation.

What Experiment 1 could not reveal is whether interlocutors were capable of generalizing on the basis of their partner's displayed knowledge. In Experiment 2 we explored this possibility using a partially-scripted online game 2 that specifically promotes the use of the N+D form.

# 3. EXPERIMENT 2: CG BELIEF-UPDATING IN A PARTIALLY-SCRIPTED DIALOG TASK

In Experiment 2, we investigated whether a partner's use of a name could lead an interlocutor to generalize about the other knowledge that partner may have. We developed a simplified name-learning game that shared some critical properties with the game in Experiment 1. This game was posted as a "HIT" on Amazon Mechanical Turk, allowing us to obtain data from a larger population. Participants learn the names of creatures while solving increasingly more challenging timed math problems, and then must choose between the Red Path or the Blue Path, and once they choose, they cannot learn names on the alternate path. Thus, participants' knowledge at the end of the game varies, depending both on their ability to solve math problems, and on their choice of path if they make it far enough into the game—a situation that mirrors the one created by the dice rolls and choice points in Experiment 1. Following the name-learning game, participants were asked to take part in a referential communication game with another participant from the name-learning game. This second game player was actually an automated agent, who we will call AutoTurk, programmed with particular experiences from the game: in one condition (RedExpert), AutoTurk was an expert who made it all the way to the end of the Red Path; in another (BlueExpert), AutoTurk made it all the way to the end of the Blue Path; and in the third (EarlyFailure), AutoTurk was a poor player, who failed out of the game by solving a math problem incorrectly after learning only two character names. We collected data regarding how participants shifted their expectations regarding partner knowledge during the course of conversation, both via explicit judgments and via their referring expression choices. We hypothesized that upon hearing a partner use a name for an item from the Red Path, participants would be more likely to believe their partner knows other Red Path names, and less likely to believe their partner knows Blue Path names.

## 3.1. Methods 3.1.1. Participants

Hundred and twenty naive adult speakers of English volunteered to participate in the study for payment via Amazon Mechanical Turk. Prior to accepting the Mechanical Turk "HIT," participants gave consent via a digital consent form approved by the Research Subjects Review Board of our institution.

# 3.2. Materials

Three novel clipart images of "cute monsters" from clipart.com were modified to create seven unique creatures from three families, each with invented names, as in Experiment 1. These creatures were presented over the course of game, whose layout is depicted in **Figure 4**. A template was used to generate five unique math problems for each participant. They were asked to solve the problems to progress through the game; each "splat" symbol on the game paths represents a math problem.

# 3.3. Procedure

#### **<IP_ADDRESS>. Instructions**

The participant, prior to accepting the HIT, read instructions describing the game, its rules and payout structure. Each participant was informed that they would be playing a game that involved two separate stages: learning the names of the cartoon creatures while solving math problems, then playing a matching game with a networked partner who had also completed the first stage. They would acquire points for each correctly learned name and correctly solved math problem during the first stage; these points would carry over into the second stage, where they would acquire points based on how well they solved the matching game with their partner. Participants were also told that if they successfully completed Stage 1 (by making it to the end of either path), they would receive a bonus payout ("Bonus 1"); another bonus payout ("Bonus 2") was based on the total number points across Stage 1 and Stage 2 combined.

#### **<IP_ADDRESS>. Stage 1**

The participant was presented with the game screen, and introduced to the first character, as depicted in **Figure 4**, and told to remember its name. They were then given 8 s to solve a simple addition problem; if successful, they advanced to the next round of the game, and were introduced to another creature. The

math problems were designed to have the form X + Y, where X and Y were both single digit numbers for the problems that were solved prior to the path-split. For the last two problems, solved after the path-split, X and Y were both double digit numbers if the participant had chosen the Red Path, while only one of X or Y was a double-digit number if the participant had chosen the Blue Path. Participants were made aware that the choice of the Red Path would entail more difficult math problems, but a higher Bonus 1 payout. If the participant successfully reached the "midpoint" of the game (after learning the third creature), they were given a Mid-test: they had to choose each creatures' name from a list of four possibilities. If successful, they were given a choice between the Red Path and the Blue Path. If the participant successfully learned both names on their chosen path, they were given a final test in which they had to again choose each creatures' name from a list of four possibilities before they could complete the path and advance to the Practice Phase. If the participant incorrectly solved a math problem or failed to successfully complete the Mid-test, their time in Stage 1 ended, and they were advanced into the Practice Phase—this allowed us to create a believable scenario in which a random participant in the game could know anywhere from 0 to 5 names.

## **<IP_ADDRESS>. Practice phase**

To ensure that participants remembered the names they had just learned, they were next presented with a series of single creatures in random order, as well as a list of 10 possible names (three were "distractor" names that did not belong to any creature), along with the options "did not learn" and "do not remember." For each creature, the participant needed to correctly identify its name if it was a creature they had learned, or correctly identify it as an unlearned name if it was a name they had not learned. If the participant chose an incorrect name, or chose "do not remember" for a name they had learned, they were reminded of the creature's name; if they chose any name at all for a creature they had not learned, they were reminded of the fact that they did not learn it. For each creature, the participant needed to correctly identify its name (or status as an unlearned creature) twice before advancing to Stage 2.

#### **<IP_ADDRESS>. Stage 2**

Participants were told that they were being connected to another Mechanical Turk "worker" who had also participated in Stage 1 of the game, and were shown a "wait" symbol and a progress bar, which changed to a "connection" symbol after a random time lag of between 2 and 90 s; in reality, they were "connected" to AutoTurk (the automated agent described earlier). Then, participants were asked to give YES/NO judgments regarding their expectation that their random partner would know each of the seven creatures. Next, participants were told they would be playing a matching game with their partner (who was actually AutoTurk). When it was the participants' turn to be the director, they were shown a single creature; their job was to decide how to refer to that creature so that their partner (actually AutoTurk) could correctly identify it from an array of four creatures.

On director trials, participants were presented with a list of 10 names and a list of 10 descriptions from which they could choose using radio buttons. They were told that if their partner chose the correct creature based on what they said, they would receive 8 points by default; if they used a name along with a description, they'd receive 5 bonus points, and if they used just the name, they'd receive 10 bonus points. If their partner chose the wrong creature based on what they'd said, they'd lose 10 points (Thus, using the name by itself if the partner does not know it would result in losing 10 points instead of gaining 18). The participant took turns with AutoTurk playing the role of director or matcher; when the participant was the matcher, they saw four creatures on the screen, and were presented with the referring expression their partner (actually AutoTurk) had selected: either N, N+D, or D. When the participant was the matcher, they received 10 points for selecting the correct item based on AutoTurk's utterance, and lost 10 points if they chose the wrong one.

Critically, the trials (shown in **Table 5**) were ordered such that it was possible for the AutoTurk to use either an N+D or a D form for particular creatures, which could then serve as a cue to the participant about whether their partner knew those creatures; in Trial 4 (a Blue Path creature), BlueExpert uses an N+D while RedExpert uses a D, and in Trial 6 (a Red Path creature), BlueExpert uses a D while RedExpert uses an N+D. Since participants should only choose the N form for a particular creature if they believed their partner actually knew the name, this allowed us to use subsequent choices between N and N+D for creatures the participant knew as a measure of their beliefs regarding their partner's knowledge.

#### **<IP_ADDRESS>. Post-Tests**

To allow us to track whether participant's explicit judgements of their partner's knowledge shifted as a result of playing the referential communication game, the participant again made YES/NO judgments regarding their belief that the partner they had worked with knew each of the creatures. They were also asked whether they had paid attention to whether their partner used names, and were asked to describe their own strategy for completing the game in Stage 2, and what strategy they thought their partner was using.

# 3.4. Results

#### 3.4.1. Explicit Judgments of Partner Knowledge

One issue worth noting is that 7% of participants, in the Post-Test, gave Yes judgments to all of the creatures; they indicated that they believed the partner they had worked with knew all of the creatures from the Red Path and from the Blue Path, which is impossible. This suggests that at least some participants did not recognize the path split during Stage 1 for what it was, and thus eliminates any expectation that these participants could draw an inference from the fact that the AutoTurk used a name from one of the two paths. Another 6% of participants gave responses that indicated they believed their partner knew creatures from later in the game but not creatures from earlier in the game: this also indicates a lack of attention to (or memory for) the overall structure of the game. These participants were excluded from our analyses.

We first compared participants' judgments regarding AutoTurk's knowledge collected prior to Stage 2 to those collected in the Post-Test. If participants were behaving optimally, then we should expect that when interacting with RedExpert, participants' judgments should shift toward YES for Trimmelor and Narpelor and toward NO for Molgirep and Bampirep. When interacting with BlueExpert, participants' judgments should show the opposite pattern. And finally, when interacting with EarlyFailure, participants should show shifts toward NO for all of the late-stage creatures. These patterns are indeed present in the data. We used a linear mixed effects regression model to predict whether the change from Stage 1 to Stage 2 judgments would be positive for individual creatures, with the AutoTurk's knowledge status as a fixed effect and the path chosen by the participant as a random effect. For Trimmelor (a Red Path creature), we found that participants interacting with BlueExpert were significantly less likely to have a positive shift (β = −1.5, S.E. = 0.4, p < 0.001), as were participants interacting with EarlyFailure (β = −0.41, S.E = 0.17, p < 0.05); participants interacting with RedExpert were significantly more likely to have a positive shift (β = 0.89, S.E = 0.14, p < 0.001). For Narpelor (another Red Path creature), we found a similar pattern; participants interacting with RedExpert were significantly more likely to have a positive shift (β = 0.81, S.E. = 0.13, p < 0.001) while participants interacting with EarlyFailure were significantly less likely to have a positive shift (β = −0.3, S.E = 0.14, p < 0.05), as were participants interacting with BlueExpert (β = −1.09, S.E. = 0.29, p < 0.0001). Overall, participants judgments following Stage 2 do reflect the evidence provided by AutoTurk's utterances.

#### 3.4.2. Referring Expression Choice

In order to look at the choice of referring expression in a meaningful way, it was necessary to restrict all analyses to only those individuals who actually knew the relevant name for that trial, and because most participants chose the higher-paying Red Path, we focus our analyses on Trials 7 and 9, in which the target creatures are the two late-stage Red Path creatures. As shown in **Table 5**, both of these trials followed references to Blue and Red path creatures, and the form of the referring expression used by AutoTurk for those creatures varied depending on AutoTurk's

knowledge. **Figure 5** shows the distribution of utterance types chosen by participants for Trimmelor (Trial 7) and Narpelor (Trial 9).

For each trial, we used a mixed effects logistic regression model to predict whether the participant would use the N form for the target creature, with AutoTurk's knowledge as a fixed effect and the path chosen by the participant as a random effect. For Trial 7, we found that participants interacting with BlueExpert were significantly less likely to use the N form (β = −2.39, S.E. = 1.15, p < 0.01). However, we did not find any significant difference in the likelihood of using the N form between participants interacting with RedExpert and EarlyFailure; even when participants interact EarlyFailure, they appear to be as likely to use the N form as participants who interacted with RedExpert, who has already used a name for a (later) Red Path creature. Thus, the results of Trial 7 only partially support the hypothesis that participants are sensitive to their partners' use of name and adapt their choice of referring expression accordingly. Note, however, that EarlyFailure simply uses descriptions all of the time, and that this is not solid evidence of a lack of name knowledge the way that using a name for a creature from the other path is.

For Trial 9, we found that participants interacting with RedExpert were significantly more likely to choose the N form (β = 2.7, S.E. = 1.2, p < 0.05) than any others, and participants interacting with BlueExpert were significantly less likely to choose the N form (β = −2.6, S.E. = 1.3, p < 0.05). Thus, at least in the final trial of the experiment, and for an item whose name RedExpert had used in an N+D form in a previous trial, participants do seem to take AutoTurk's knowledge into account in their choice to use a name.

We also examined participants' Post-Test descriptions of their own strategy and their beliefs regarding their partner's strategy. Here, we found that most participants focused on the memoryrelated challenges of the task, commenting on how they kept the creatures' names straight and on how difficult that was. But based on the participants' post-hoc reflections on strategy, some individuals believed themselves to be sensitive to the information shared by their partner in the form of their choice of referring expression, and were aiming to make "optimal" referring expression choices based on that information. Many of these participants commented that they thought their partner was using the same strategy, but "doing a better job of it." But as we noted, the primary focus of participants in their Post-Test comments was on the challenges posed by the memory task; this may suggest that the basis for the inferences we were interested in testing (the overall structure of the game and the names contained within it) was either not recognized or misremembered by some participants.

# 3.5. Experiment 2 Discussion

Participants were able to generate more accurate beliefs regarding what their partner knew following interaction with that partner. In the Post-Test, participants changed their beliefs in the expected direction given the knowledge displayed by AutoTurk; thus, even in this simplified game environment, participants are capable of using their partner's utterances to arrive at a more accurate set of beliefs regarding their partner's knowledge.

The participants' referring expression choices also support our generalization hypothesis: in the final trial, we found that participants were significantly more likely to use a name to refer to final Red Path creature if they were interacting with RedExpert. Preceding trials paint a somewhat messier picture regarding the relationship between AutoTurk's utterances and the participants' choice of referring expression, particularly in the case of participants interacting with EarlyFailure. However, it's worth remembering that in Experiment 1, participants' use of names did not fully reflect their knowledge; participants often used descriptions even when they did, in fact, know the names. In the context of Experiment 2, this means that it is not necessarily valid to make the inference that because EarlyFailure used a description, it must not know the name. But we still would have expected participants interacting with EarlyFailure to use the N+D form, rather than using names by themselves, given the

lack of evidence for knowing names. Still, participants interacting with BlueExpert were the least likely to use names; it seems that participants could in fact generalize from BlueExpert's use of the N+D form for a Blue Path creature, and infer that BlueExpert could not possibly know the name of a Red Path creature.

Given the extent to which the kinds of belief updating we are interested in would depend on both accurate mental representations of the structure of the knowledge domain and attention to the partner's utterances, the combination of Mechanical Turk and novel knowledge may not have been a good one. Though many psychological findings have been successfully replicated using Mechanical Turk (e.g., Munro et al., 2010; Crump et al., 2013), the Mechanical Turk platform by itself does nothing to promote attention to the task unless the creator of the HIT creates incentives in the form of bonuses for work that meets some kind of standard. But in developing the bonus scheme to motivate participants to attend to the task in Experiment 1, we might have been probing participants' gambling behavior, rather than their conversational behavior: would a participant be willing to risk losing 10 points for the chance of gaining 18? What if the point spread were different? And indeed, many participants commented on making this calculation as if it were a bet, when they described their strategy in the Post-Test.

Even more important, though, is the difficulty that participants had remembering the names and the overall structure of the game in Stage 1. Based on their Pre-Test responses, participants struggled to remember which creature was which, and many of them seemed not to remember the order in which creatures were learned (or even that the path split meant that some creatures could not be learned together), and thus it seems unlikely that the kinds of memory associations that would be necessary in order for category-related cues to be useful for referring expression choice would even be present for these participants. These memory and knowledge-structure issues are crucial areas for future work; it seems likely, for example, that a sleep interval may be necessary in order to develop the kinds of concept associations necessary for these inferences (Stickgold and Walker, 2013; Landmann et al., 2014).

# 4. GENERAL DISCUSSION

Experiments 1 and 2 demonstrate that interlocutors are capable of using information gained over the course of conversation, particularly the information conveyed by the partner's choice of referring expression, to update their expectations regarding what knowledge is shared with their partner, and that these belief updates influence speakers' choice of referring expressions during subsequent conversation. In Experiment 2, we found some evidence for generalization, in that participants interacting with BlueExpert were the least likely to use the N form for a subsequent reference to a Red Path creature; the demonstrated knowledge of Blue Path names allowed participants to generalize to a necessary lack of knowledge of Red Path names. These findings have important implications for theories of CG use during conversation.

In many theories, the distinction between knowing that a referent is in CG (and is thus something to which the speaker could felicitously refer) and knowing that a particular means of referring to that referent is likely to be understood by the addressee, seems to be either blurred or non-existent. Yet even in those cases where an object is clearly in CG via a cue like visual co-presence (as in "cubbyhole" studies, e.g., Keysar et al., 2000), the speaker still has to decide what to call it. Even for common nouns, we usually have a choice regarding which to use to refer to a particular item: do we call something a cassette or a tape? While a number of factors influence this decision (word frequency, the other items in the display, etc), one of these should surely be whether or not the addressee is familiar with the link between a particular expression and the referent. This is especially true for proper names, which are arbitrary labels for a referent, and can only be understood by those who know about the link between the label and the referent. But it seems possible that various kinds of referring expressions could come to serve, under certain circumstances, as context-dependent conventions for referring (in other words, as context-dependent names), and this may be a way of connecting the work presented here to studies of lexical precedents or conceptual pacts (e.g., Metzing and Brennan, 2003; Brown-Schmidt, 2009). Partner-specific expectations relating to the means of referring could also play a role in comprehension, and in pilot work building off Wolter et al. (2011), we are currently exploring whether a speaker's use of a scalar contrast (e.g., the big candle) generates an expectation that the contrast item will be called the small candle even when the contrast is no longer present, by looking for reduced cohort competition effects with a competitor like candy.

We suggest that what is truly needed in an account of CG for definite reference is not triple co-presence of the sort described by Clark and Marshall (1978, 1981), but rather, quadruple copresence: there must be some record in memory that links the speaker, the addressee, the object, and a particular means of referring to that object in order for a speaker to have a reasonable expectations that their use of that means of referring to that object will be understood by their addressee. Community membership can provide a powerful cue to such co-presence; we can often safely assume that certain means of referring to objects will be known by people by virtue of who they are and the communities to which they belong. This does not necessarily require any elaborate representations along the lines of the reference diaries proposed by Clark and Marshall; indeed, if this kind of knowledge can be drawn upon via the associative mechanisms proposed by Horton and Gerrig (2005a,b), it could underlie the kinds of beliefupdating we described earlier. If we learn through conversation that our partner is the member of a particular community, this may trigger associations with the kinds of knowledge members of that community have (both in terms of referents and in terms of means of referring to those referents) that could lead to more accurate estimates of CG. And in particular, the evidence that could trigger such associations could come through our partner's use of an N+D form, as suggested by the results of Experiments 1 and 2, since that form enables speakers to display knowledge of a name without making any assumptions about whether it is shared with their addressee.

But not all displays of knowledge are equivalent. Finding out that an interlocutor knows the name Statue of Liberty or guitar is not particularly informative, as nearly any speaker of English would know those names. But evidence that the speaker knows the name South Street Seaport or viol da gamba should cause their conversational partner to shift toward believing their fellow interlocutor has expertise with New York City landmarks or Renaissance-era stringed instruments, respectively. If language comprehension is, in part, a process of trying to explain why the speaker said what they said the way that they said it (as in, e.g., Hobbs et al., 1993), then the explanation we seek may be rooted in what we think the speaker knows. Bayesian beliefupdating could provide a useful framework for exploring the extent to which interlocutors use evidence to generate such explanations in a rational way, based on the informativity of the evidence provided by their partner. We have ample evidence that during interactive conversation, interlocutors adapt their expectations regarding such things as the likelihood of particular syntactic constructions (e.g., Kleinschmidt et al., 2012; Fine et al., 2013) or of particular phonetic realizations (e.g., Kleinschmidt and Jaeger, 2015), and both of these adaptation phenomena have been successfully explored using Bayesian belief-updating models. Future work in this area should focus on understanding the process by which people generate, update, and generalize beyond their prior expectations regarding partner knowledge; games like the ones used in Experiments 1 and 2 may provide a fruitful paradigm for exploring these processes in more detail,

## REFERENCES

particularly as they relate to the relative informativity of a particular knowledge-display.

The choice of referring expression is a valuable tool for exploring questions about how we use CG. Even in those cases where an object is physically co-present and therefore can be referred to using a definite NP, speakers still must decide what to call it; thus, it is crucial not to think about CG simply in terms of what interlocutors know about what their conversational partner can see, but to also consider what interlocutors believe about what their partner knows. What's in a name? Evidence about knowledge.

## AUTHOR CONTRIBUTIONS

All authors listed, have made substantial, direct and intellectual contribution to the work, and approved it for publication.

# ACKNOWLEDGMENTS

We would like to acknowledge Chelsea Marsh for her assistance with recruiting, training, scheduling, and testing participants in Experiment 1, and members of the KurTan lab and the Center for Language Sciences at the University of Rochester for fruitful discussion and feedback. Funding: This research was supported by National Institute of Child Health and Human Development Grant HD-27206 to MT.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2016 Gegg-Harrison and Tanenhaus. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# The Role of Metarepresentation in the Production and Resolution of Referring Expressions

#### William S. Horton<sup>1</sup> \* and Susan E. Brennan<sup>2</sup>

*<sup>1</sup> Department of Psychology, Northwestern University, Evanston, IL, USA, <sup>2</sup> Department of Psychology, Stony Brook University, Stony Brook, NY, USA*

In this paper we consider the potential role of metarepresentation—the representation of another representation, or as commonly considered within cognitive science, the mental representation of another individual's knowledge and beliefs—in mediating definite reference and common ground in conversation. Using dialogues from a referential communication study in which speakers conversed in succession with two different addressees, we highlight ways in which interlocutors work together to successfully refer to objects, and achieve shared conceptualizations. We briefly review accounts of how such shared conceptualizations could be represented in memory, from simple associations between label and referent, to "triple co-presence" representations that track interlocutors in an episode of referring, to more elaborate metarepresentations that invoke theory of mind, mutual knowledge, or a model of a conversational partner. We consider how some forms of metarepresentation, once created and activated, could account for definite reference in conversation by appealing to ordinary processes in memory. We conclude that any representations that capture information about others' perspectives are likely to be relatively simple and subject to the same kinds of constraints on attention and memory that influence other kinds of cognitive representations.

#### Edited by:

*Kees Van Deemter, University of Aberdeen, UK*

#### Reviewed by:

*Stanka A. Fitneva, Queen's University, Canada Dale J. Barr, University of Glasgow, UK*

#### \*Correspondence:

*William S. Horton<EMAIL_ADDRESS>
#### Specialty section:

*This article was submitted to Language Sciences, a section of the journal Frontiers in Psychology*

Received: *14 September 2015* Accepted: *11 July 2016* Published: *27 July 2016*

#### Citation:

*Horton WS and Brennan SE (2016) The Role of Metarepresentation in the Production and Resolution of Referring Expressions. Front. Psychol. 7:1111. doi: 10.3389/fpsyg.2016.01111* Keywords: reference, common ground, metarepresentation, memory, cognitive models

# REFERRING AND REPRESENTATION

Speakers have many options in the production of referring expressions, ranging from simple pronouns to complex definite or indefinite noun phrases. Moreover, there is potential for substantial variability in the noun phrases speakers choose. Consider just a few of the referring expressions for the novel object in **Figure 1**, each used by a different pair of speakers.

Successful referring—with the desired effect of getting a speaker and an addressee focused on the same referent—is as much about an interactive process as it is about a product. The expressions in **Figure 1** emerged from dialogues such as the following, collected during an experiment by Stellmann and Brennan (1993), in which a director, A, is trying to help a matcher seated behind a screen, B, to match a dozen cards with abstract geometric figures (tangrams) into a target order (Note: Overlapping speech occurs within <sup>∗</sup> asterisks<sup>∗</sup> ).

	- B: A candle... ok...
	- A: It's got a lot∗of<sup>∗</sup>

Here, A begins by proposing that the object in question resembles a candle, but B is unable to recognize any suitable object in the set and asks for clarification. A, guessing which object B might be considering, suggests rotating the card. B attempts to discuss the card's geometric details, but after a few exchanges focused on the geometry of the object, A tosses out a new counter-proposal (someone doing a split on the ground or jumping in the air, yeah, with bell bottoms on). B eventually confirms this perspective and places the corresponding card on the board; this action provides evidence for the success of the referring process. In this exchange, after 16 conversational turns, speaker and addressee have finally come to believe that they mean the same thing. Thereafter, A and B referred to this object again on subsequent rounds as follows (note that the exchanges in these rounds are each separated by matches to an average of 11 other objects):

	- A: Ok um wait alright ok
	- B: Got it

Round 4: B: The bell bottomed jumper A: I had it there man

This example is representative of how 26 pairs of subjects in this experiment referred to the 12 objects that they repeatedly matched over four rounds. The processes through which people interactively seek and provide evidence for shared perspectives during referring in conversation is known as grounding (Clark and Wilkes-Gibbs, 1986; Clark and Schaefer, 1989; Clark and Brennan, 1991). The consistency among referring expressions produced by A and B across rounds, as well as the evidence provided in each round by the successful match of the matcher's object to the director's, suggest that for each object, the two partners built up common ground that enabled them to mentally represent the object in the same way (or highly similar ways). As the same time, the variability of expressions in **Figure 1** suggests that other pairs conceptualized this object quite differently. Through such processes of conceptual coordination, partners converge on, and re-use the same terms within a conversation, displaying lexical and conceptual entrainment in their choices of referring expressions (Garrod and Anderson, 1987; Brennan and Clark, 1996).

What sorts of cognitive mechanisms support such coordination? There have been several types of answers to this question. Perhaps the simplest is one that appeals to direct cross-speaker activation of particular expressions, as proposed by the interactive alignment account (Pickering and Garrod, 2004). This account presumes that interlocutors converge on the same referring expressions simply because one speaker's utterances can automatically prime similar responses from the other, facilitating similar discourse representations over time (assuming that the interlocutors are similar). A compatible view, from Brown and Dell (1987; Dell and Brown, 1991), suggests that what appears to be partner-specific coordination is often actually generic, in that what is easy for a speaker to produce tends to be easy for an addressee to understand. Relevant claims for this view include that "speakers and listeners do not routinely take common ground into account during initial processing" (Pickering and Garrod, 2004, 179), and that "normal conversation does not routinely require modeling the interlocutor's mind" (ibid, p. 180). Pickering and Garrod's proposal is consistent with models that propose that common ground is used only on demand, when repair is needed (e.g., Brown and Dell, 1987; Horton and Keysar, 1996; Keysar et al., 2000):

"Establishment of full common ground is, we argue, a specialized and non-automatic process that is used primarily in times of difficulty (when radical misalignment becomes apparent)... speakers and listeners do not routinely take common ground into account during initial processing... full common ground is only used when simpler mechanisms are ineffective" (Pickering and Garrod, 2004, p. 179).

Much experimental work by Keysar, Barr and colleagues (e.g., Keysar et al., 2000; Barr and Keysar, 2002; Keysar et al., 2003) has been presented in support of this idea, suggesting that interlocutors in conversation behave egocentrically (at least at first), but that this does not hamper communication as long as interlocutors are similar enough and happen to inhabit the same context (see also Shintel and Keysar, 2009).

Another type of answer to the question of conversational coordination involves the notion of metarepresentation, which generally refers to the representation of another representation. Sperber (2000, p. 3) identified four main categories of metarepresentation: "Mental representations of mental representations (e.g., the thought, "John believes that it will rain"), mental representations of public representations (e.g., the thought, "John said that it will rain"), public representations of mental representations (e.g., the utterance, "John believes that it will rain"), and public representations of public representations (e.g., the utterance, "John said that it will rain")." Accounts of language use often assume, either implicitly or explicitly, that definite reference requires some form of the first of these, or the mental representation of another's mental representation—typically considered as the representation of another person's knowledge, needs, or beliefs. Certainly, Grice's (1975) original notion of conversational implicature was inherently metarepresentational in this sense, being rooted in the idea that pragmatic meanings involve direct consideration of what is mutually known between rational speakers. Similarly, linguistic theories of reference production frequently assume that choices in the form and content of referring expressions emerge from speaker's assessments of the accessibility of particular referents in the minds of their addressees (e.g., Gundel et al., 1993; Grosz et al., 1995). And models of communication and intention recognition in computational linguistics and logic have often been focused on providing formalizations of representations of other agent's epistemic states (e.g., Cohen and Perrault, 1979; Ditmarsch et al., 2007). An important question for all of these approaches, of course, is how well they succeed in capturing the kinds of knowledge state inferences that human interlocutors are likely to make in real time during genuine interactions.

Theories appealing to the mental representation of other's mental representations often presume detailed consideration of the needs, knowledge, or beliefs of a social partner. For example, the influential notion of theory of mind, as first articulated by Premack and Woodruff (1978), and refined further by Dennett (1978) and Pylyshyn (1978), refers to an individual's mental capacity to reason about the mental states of others, an ability that appears to follow a distinct developmental trajectory into adulthood (Wellman et al., 2001; Apperly, 2011, 2013). An even more complex way to think about metarepresentation invokes the recursive modeling of mutual knowledge (I know X; you know X; I know that you know X; you know that I know X; I know that you know that I know X; and so on); however, it is widely acknowledged that this sort of recursive reasoning would be so resource-intensive as to be implausible [see the debates in Smith (1982) on this mutual knowledge paradox, and Clark and Marshall's (1978, 1981) proposed solution involving inferences about co-presence].

Given the apparent ease with which interlocutors plan and resolve referring expressions in conversation, it might seem prudent to prefer the simplest account that relies on "priming" of referent-label associations across interlocutors. However, experimental corpora such as Stellmann and Brennan (1993) raise some key questions about the nature of the representations underlying referential communication that cannot be explained by simple associations alone (see similar evidence presented by Brennan and Clark, 1996 and Horton and Gerrig, 2005b).

To that end, it is important to note that Stellmann and Brennan's experiment actually involved quartets of speakers. Two additional subjects, C and D, matched the same cards at the same time as A and B, but in a neighboring room. For the item shown in **Figure 1**, C and D entrained on a perspective that they ended up labeling as the anchor. Crucially, after both pairs matched the cards for Rounds 1–4, they were split up and re-paired such that A and D completed Rounds 5–8 together, as did B and C. Of interest was whether there would be any savings in the linguistic effort needed to match these now-familiar objects. Here is what ensued between A and her new partner, D, in Round 5 immediately after the partner switch:

What is striking is that the director, A, did not simply pick up where had she left off with B, with the concise expression that had worked most recently ("the bell bottomed jumper") even though this would presumably have corresponded to the strongest trace in memory (according to Garrod and Anderson, 1987 output-input coordination principle, a precursor to the interactive alignment theory). Instead, she proposed an indefinite referring expression marked as tentative by hedging ("ah the second one looks like maybe a person jumping in the air who is wearing bell bottoms"), as if to display sensitivity to the fact (that is, mentally representing) that she as yet had no common ground with D. She also proffers an alternative expression, "or it could be a candle." Such re-conceptualizations have been observed in other referential communication studies that involve switching from an old to a new conversational partner (e.g., Brennan and Clark, 1996; Horton and Gerrig, 2005b; Gorman et al., 2013). After D failed to accept either of the (re-conceptualized) perspectives that A had discussed with her old partner, the new partners ended up converging on the perspective that D happened to entrain on earlier with C in the other room. Meanwhile, in that other room, B and C struggled valiantly (over 27 turns) to arrive at what might best be described as a hybrid perspective (bell-bottom anchor), which they continued to use in their next 3 rounds together. Although all of these people were, by then, individually quite familiar with the object in **Figure 1**, they still had to expend significant effort to ground their references to this object with their new partners in Round 5, just as with their initial partners in Round 1.

In the last stage of Stellmann and Brennan's experiment, the original partners were reunited for four final rounds, 9– 12: A joined up again with B again, and C with D, whereupon they matched the same cards again. At that point, A and B reverted immediately and efficiently to the perspective they had entrained on previously, using "the guy with the bell bottoms jumping," "the bell bottom," "the bell bottomed guy," and "the bell bottomed man" respectively in Rounds 9–12. Likewise, C and D immediately returned to the unadorned definite expression "the anchor" as soon as they got back together in Round 9. That pairs often switched back smoothly in Round 9 to the relatively short expression they had entrained upon in rounds 1–4 suggests that their representations included more than just the association of a referent and a referring expression (or the perspective it indexes), but information about the communication partner as well.

In this article, we suggest that simple associations are not sufficient to account for these and similar patterns of conversational referring. As an alternative possibility, we examine the role of metarepresentations in communication, and whether representations of a partner's goals, informational needs, or knowledge must, by necessity, involve the kinds of timeconsuming inferences most commonly associated with theory of mind. We consider whether metarepresentations are created, maintained, and used routinely during conversational episodes, or only strategically in response to special circumstances such as evidence of misunderstanding. At the same time, we will appeal to an explanation relying on ordinary memory processes such as resonance (Ratcliff, 1978), and avoid positing any sort of "special" memory representation or separate stage of processing to account for the apparent effects of common ground upon referring in conversation. We conclude that a simple (meta) representation about a conversational episode (once created and activated) could be rapidly re-instantiated into the current discourse context via simple cues.

# METAREPRESENTATION IN THEORY OF MIND

As stated previously, the notion of metarepresentation has been especially important within the literature on theory of mind (ToM), which refers to the capacity to reason about the mental states of others. A large body of research has sought to answer such questions as whether theory of mind is a uniquely human capacity, whether deficits in theory of mind can help explain particular social and communicative disorders such as autism and schizophrenia, and whether theory of mind abilities are mediated by unitary, specialized neural circuits in the brain (e.g., Call and Tomasello, 2008; Frith and Frith, 2012; Baron-Cohen et al., 2013).

As a rule, ToM is fundamentally important for making sense of the social world.  Based on your capacity for mental state attribution (and your knowledge of keys and doors), you might reasonably infer that this person has the intention of unlocking the door. Some (e.g., Perner and Ruffman, 2005; Penn and Povinelli, 2007) have argued that expectations about another's behavior could be generated primarily on the basis of associative or statistical knowledge concerning the kinds of actions that involve, for example, keys and doors, without being mediated by a theory of mind inference, although others have argued that simple associations or rules cannot account for the range of contexts across development in which young children, in particular, come to show evidence for perspective-taking (Baillargeon et al., 2010). Because a person's (private) intentions are not directly observable, one can only use observations of behavior to make inferences about the mental states giving rise to those behaviors. Making such inferences is a form of "mindreading"—reasoning about another's internal mental state—and is the hallmark of how people engage their theory of mind (Apperly, 2011).

In principle, mindreading can involve a wide range of mental state attributions, including inferences about emotional states, perceptual access, and desires and goals. The empirical literature on ToM (and certainly the developmental literature) has commonly focused on situations that involve deliberative, reflective assessments of another person's knowledge, most often involving "false belief," in which another's knowledge conflicts with reality (Baron-Cohen et al., 1985; Wellman et al., 2001). For example, the classic Sally-Ann task (Wimmer and Perner, 1983) asks children to reason about Sally's belief concerning the location of an object, which, unbeknownst to her, has been moved from its original location. To pass this task, a child must recognize that Sally possesses an incorrect belief about the object's location, be able to understand that the question is asking where she would (rather than should) look for it, and respond accordingly to the experimenter's question. Quite clearly, this requires access to metarepresentations of Sally's beliefs. One must not only represent what Sally believes, but must also be able to appreciate how Sally's beliefs differ from one's own (and from reality). The representational and computational challenges involved in such situations have been cited as one reason why children don't consistently pass classic false belief tests until after the age of four (e.g., Call and Tomasello, 1999; Bloom and German, 2000).

Much of the literature on theory of mind, though, suggests that adults, at least, have the ability to construct and access representations of another's knowledge, even if they don't always apply this ability in situations that require puzzling out what another person is likely to believe, or how they are likely to act (Keysar et al., 2003). It is not immediately evident, though, whether the types of deliberative mental state attribution required by experimental tasks exploring false belief and theory of mind are qualitatively similar to the kinds of spontaneous inferencing regarding common ground that would seem to take place during routine conversation. Moreover, the types of mental state attribution commonly presumed within the literature on theory of mind have often assumed a view of metarepresentations as discrete, neatly packaged, deterministic bits of information about other people's knowledge and beliefs. Experiments exploring this capacity most often probe for "ondemand" inferences based on the presence or absence of knowledge, as in the classic Sally-Ann task, rather than measuring probabalistic inferences that occur spontaneously. Exceptions include work by Samson, Apperly and colleagues (e.g., Samson et al., 2010; Surtees and Apperly, 2012; see also van der Wel et al., 2014) who have shown that both children and adults can use extremely simple cues, such as the direction of attention, to rapidly generate inferences about mental states. Moreover, responding correctly to the classic Sally-Ann task requires the ability to respond to a question that depends on understanding modal verbs. When 3-year-olds are simply asked to act out "what happens next?" upon Sally's return to the hidden-object situation, they are more likely to demonstrate a spontaneous ability to reason about ToM and respond correctly (Rubio-Fernández and Geurts, 2013).

Such evidence suggests that, while it can take time to reason (on demand) about another person's knowledge or beliefs, once a relevant metarepresentation has been evoked, taking account of a partner context need not involve a time-consuming (or even a very mature) process of reasoning. This information can be used just like any other information in memory.

# REFERENCE DIARIES AND TRIPLE CO-PRESENCE

Metarepresentation in some form is often invoked by accounts of referential communication. Perhaps the most influential account of definite reference comes from Clark and Marshall (1978, 1981), who observed, "people's memory must be organized to enable them to get access to evidence they will need to make felicitous references. To make or interpret definite references people have to assess certain "shared" knowledge. This knowledge, it turns out, is defined by an infinite number of conditions. How then can people assess this knowledge in a finite amount of time?" (Clark and Marshall, 1981, pp. 56–57). After rejecting recursively-achieved mutual knowledge as cognitively implausible, Clark and Marshall proposed that interlocutors take advantage of representations they called "reference diaries" that encode evidence for triple co-presence—or evidence that the speaker, addressee, and referent were "openly co-present together" (1981, p. 32). On this account, definite expressions (such as those in **Figure 1**) are constructed and interpreted against the common ground established by interlocutors through a heuristic that shortcuts the problem of computing mutual knowledge recursively. This heuristic is based on an inference that the parties in a conversation perceive or recall common ground based on what they've discussed together (linguistic copresence), their experiences together in the same environment (physical co-presence), or their presumed socio-cultural overlap (community co-membership). Prior co-presence is established through previous experience together, whereas potential copresence is evoked by a speaker's rational expectation that an addressee can use the current context to understand, for example, the intended referent of I'd like that loaf of bread please when accompanied by a pointing gesture over the addressee's shoulder (Clark and Marshall, 1981; for discussion, see Polichak and Gerrig, 1998). An inference on the part of a speaker that she and her addressee are contextually co-present presumably supports some kind of suitable representation of partner-specific information that facilitates audience design (Clark and Murphy, 1982; Bell, 1984; Horton and Gerrig, 2002), allowing her to produce referring expressions that a particular addressee is likely to be able to resolve. Such representations also allow addressees to interpret the same referring expression differently when it is spoken by different speakers in different contexts (Metzing and Brennan, 2003).

Clark and Marshall (1981) were not specific about the characteristics or limitations of possible partner-specific representations (which we call metarepresentations), apart from proposing that they encode triple co-presence (an association linking the self, an other, and the information in question). However, in their sections on organization of memory and components of memory, they referred to episodic memories of events that speakers and addressees have experienced together as "compartmentalized into useful units" that can be selectively accessed (p. 55), and that shift when the interlocutor changes in a conversation.

Ongoing debates in psycholinguistics have focused on the extent to which consideration of common ground routinely and initially informs language processing (Brennan and Hanna, 2009), or whether it is invoked in a separate stage of processing, like a repair (e.g., Brown and Dell, 1987; Keysar et al., 2000; Pickering and Garrod, 2004) Where Clark and Marshall and their critics agree is that sometimes effort must be expended in order to establish common ground or to propose or resolve a referring expression, but that frequently, referring in conversation seems effortless. The question remains as to what sort of representation underlies processing in this latter situation.

# A ROLE FOR METAREPRESENTATIONS IN REFERRING

In principle, the notion of metarepresentation would appear to be central to models of reference and language use. An important question is whether considering metarepresentations need always be resource-intensive and time-consuming, or whether people can rapidly, and potentially automatically, behave as if they have access to appropriate metarepresentations under the right circumstances. In this section and the next, we argue that the metarepresentations themselves need not be elaborate or encode inferences about complex mental states, but can be simple and partial, driven by current conversational purposes. Furthermore, we propose that once a suitable episodic metarepresentation has been activated, it may be used as fluidly and rapidly as any other information available in memory.

In contrast, some have argued that speakers and addressees are inevitably "egocentric," and that taking account of a partner's perspective as distinct from one's own can happen only as a kind of delayed processing or repair (Keysar et al., 1998; Epley et al., 2004). Shintel and Keysar (2009) point out that "elaborate reasoning that requires interlocutors to keep updated metarepresentations of the other's beliefs that are separate from their own representations of the situation is both time consuming and cognitively demanding." Not surprisingly, experiments that place speakers in perceptual contexts with both salient privileged information and information that is in common ground with an addressee, along with the need to continuously distinguish these, show evidence for interference between dueling perspectives (Horton and Keysar, 1996; Keysar et al., 2000). Indeed, some have used this kind of evidence to argue for modularity in cognitive architecture (Barr, 2008).

A related argument is that what appears to be partnerspecific processing (resulting, e.g., in entrainment and audience design) occurs simply when speakers and hearers happen to share the same context, as suggested by Pickering and Garrod's (2004) interactive alignment model (see also Brown and Dell 1987). As Pickering and Garrod argue, simple priming can facilitate convergence in referring expressions without obligating interlocutors to directly represent the other person's perspective. On these accounts, metarepresentations would have little role to play in fundamental aspects of language processing, instead being relevant only in the context of slower, more effortful processes of monitoring and repair.

In this context, we make two critical points about referring in conversation. The first critical point is that referring is not a deterministic process, but a collaborative one that involves coordination between (at least) two people. As a result, any form of metarepresentation that emerges from conversational grounding is likely to be highly probabilistic, in the sense that the relevant memory traces will vary in strength and accessibility. To understand why, we return to our examples from Stellmann and Brennan's corpus and focus more closely on what happened after the partner-switch at Round 5. Here, D began with a couple of proposals to her new partner, B; she first proposed the perspective that had worked well earlier with her former partner C, and then added another perspective that C had failed to take up:

Here, by echoing some of D's words hesitantly, B provides evidence of uncertainty; he's considering this proposal but isn't able to accept it. D responds by trying to motivate the jumping man with bell bottoms using a lengthy and laborious geometric description, but then B suggests returning to a figurative strategy:

B: You can't make a picture out of it?

After two more proposals, D fortuitously hits upon the perspective that B happened to use earlier with former partner A: "let's call it an anchor." This works, and on they go. Examples like this underscore a critical aspect of Clark and Marshall's original co-presence account (Clark and Brennan, 1991; Clark, 1996), which is that heuristic-based approximations of what others know may suffice much of the time, given that grounding and the potential for interaction provide relatively inexpensive ways to recover if and when interlocutors get it wrong. Speakers' current purposes often don't require them to be perfect or to work too hard on the inferences they make. They are thus able to balance the costs of delaying an utterance (in order to plan it more fully) with the risks of appearing to be inattentive or losing their partners' attention or running out of time in a task (Clark and Brennan, 1991).

A second critical point is that evidence for representation can be found in how a speaker presents a particular referring expression. Referring expressions can be fluent, disfluent, brief, wordy, hedged, or presented with falling or question intonation (Smith and Clark, 1993; Brennan and Williams, 1995). As the examples from Stellmann and Brennan's corpus illustrate, a referring expression, once proffered, has the potential to be (and be marked as) tentative, vague, or unacceptable, suggesting that any representation of another's knowledge that might emerge through conversational grounding also has the potential to be incomplete or incorrect. Moreover, given that referring expressions and other types of utterances are generally produced and understood on a time scale that would seem to preclude lengthy deliberation, there must be processes that permit reasonably rapid access to perspective-relevant information. These factors impose critical constraints upon any account attempting to capture the nature of successful referring in language use.

As the speakers in Stellmann and Brennan's study transitioned from one partner to another and back again, the way in which they framed referring expressions changed accordingly, as described previously. One possible explanation for the hedging after the first partner change in Round 5 is that the presence of the brand-new partner, D, weakened the memory trace for the previous referring expression. However this explanation by itself is not so convincing, as the repeated referring in Rounds 1–4 with partner B should have rendered A's memory for what to call this object quite strong. Moreover, the return to Partner B in Round 9 (when the original pairs were reunited) showed little to no disruption due to the partner switch, but rather a smooth return to the originally entrained-upon perspective. Reverting to this original perspective might be expected to fight against one's memory traces for the repeated (and more recent) references to the anchor in Rounds 5–8. However, a plausible explanation is that the partner-switch successfully boosted accessibility of the previous episode, likely through a compound cue comprised of the current referent plus the presence of the original partner B (Ratcliff and McKoon, 1988; Horton and Gerrig, 2005a, in press).

At issue is when and how such a shift in referring expressions also might be shaped by remembering that the original partner shares a particular perspective on the tangrams not shared by the other partner. If so, we can ask if and when this belief is encoded as part of the original memory trace for this interaction. The tentative way in which A expresses "looks like maybe a person jumping in the air who is wearing bell bottoms" is presumably not due to A's own lack of facility with this perspective (which, after all, A had just finished deploying over and over with B), but may, in fact, be caused by A's sense that a new partner, D, would not find it so easy to take this perspective (in other words, that D is not implicated in A's episodic representation). In principle, the difference between proposing the efficiently packaged definite expression "bell bottomed jumper" vs. "looks like maybe a person jumping in the air who is wearing bell bottoms" would seem to involve ready access to suitable representations that encode such beliefs about another's knowledge. As we suggest, though, the availability of such representations is likely to be influenced by the nature of the grounding processes that give rise to these beliefs, providing speakers with the opportunity to encode inferences concerning what can be taken as shared—especially when these inferences are supported by salient features of the conversational context.

It is not clear how this apparently partner-specific effect on the forms of utterances would be handled by Pickering and Garrod's simple priming account, or by the "output-input coordination" principle of Garrod and Anderson (1987), which predicts that a speaker should continue to use the same expression that worked last time (regardless of addressee). As we argue in the next section, though, there are good reasons to eschew an account of common ground processing that relies on detailed metarepresentations of other's knowledge. But, assuming much simpler types of representations for purposes of conversational interaction need not doom individuals to egocentrism. Both of the accounts that we describe next support ways in which "ordinary" partner-relevant representations could give rise to felicitous language use that are consistent with constraints based on cognitive capacities of individual speakers and salient features of conversational contexts.

# ORDINARY MEMORY AND "ONE BIT" REPRESENTATIONS

The examples from Stellmann and Brennan's corpus demonstrate that when speakers use a referring expression, they can depend on their addressees to let them know if a referent is unclear. They can take the risk of starting to speak in a timely manner, designing referring expressions based on available representations that are likely (but not guaranteed) to work. If we accept that ordinary conversational reference is unlikely to occur in a resource-intensive manner qualitatively similar to the deliberative consideration of false belief, and if we accept that low-level priming explanations such as outputinput coordination (Garrod and Anderson, 1987) or interactive alignment (Pickering and Garrod, 2004) fail to adequately account for audience design, the question remains as to how interlocutors so often are able to refer to objects in ways that are generally consistent with shared knowledge. Here, we consider two accounts that do not see fully elaborated partner models as being necessary for particular referring expressions to succeed indeed, both emphasize the fact that, in conversation, success is not guaranteed. Specifically, these accounts are the "memorybased" account described by Horton and Gerrig (2005a, in press), and the "one-bit" account described by Galati and Brennan (2006; 2010; see also Brennan and Hanna, 2009).

These two accounts complement each other, in that both connect the dots between memory representations and audience design, with each emphasizing a different launching point: The memory-based account begins with ordinary memory processes and representations, in order to consider how apparent instances of audience design emerge fluidly in conversation, whereas the one-bit account begins with audience design or partner specific processing in conversation, in order to consider what sorts of context-augmented representations (or common ground) could underlie ordinary language processing. Common to both accounts is the idea that partner-specific referring in conversation is mediated through ordinary memory representations (without appeal to special or elaborate mechanisms of the kind entailed by the notion of reference diaries or theory of mind). Both accounts reject as implausible (and computationally expensive) the idea that people routinely "tag" (and continually make triple co-presence inferences about) every element of information that could be relevant to "common ground." Both accounts endorse the view that relevant representations frequently include contextual information concerning a conversational partner, but that there is nothing qualitatively "special" about this information that gives it priority over other relevant information (see Goldinger, 1998 for a similar view).

Moreover, the extent to which person-centered information might be individuated in ways that reliably support felicitous reference will, on both accounts, depend greatly on factors such as immediacy, relevance, perceptual vividness, and goals, as well as whether such information has already been processed in the conversational context. In these respects, both the onebit view and the memory-based view highlight how routine cognitive considerations strongly shape the extent to which people show evidence for consideration of common ground. On these accounts, successful definite reference depends on simpler representations that support rapid access to contextually relevant knowledge.

The memory-based model (Horton and Gerrig, 2005a, in press) is a cognitively motivated account explaining how language users could gain access to partner-relevant information in ways that require neither special-purpose representations nor special-purpose processes. More specifically, Horton and Gerrig (2005a) described how considerations of common ground could occur on the basis of ordinary representations as they become accessible from memory through ordinary means. For instances of "personal" common ground in particular (Clark, 1996), these memory representations were characterized as rich episodic traces of previous encounters with others, representing the products of the kinds of encoding typical of one's experiences of particular events.

Once such traces are encoded into memory, subsequent encounters can trigger the automatic retrieval of relevant memory traces, through a process termed resonance. Inspired by cue-driven retrieval processes found in models of recognition memory (Ratcliff, 1978; Gillund and Shiffrin, 1984; Hintzman, 1986; Ratcliff and McKoon, 1988), resonance involves the parallel activation of information that shares overlapping features with the memory probe (e.g., the presence of an interlocutor). When resonance reaches some threshold, which itself is a function of the recency and frequency with which a memory has been previously retrieved, this information can become accessible in a way that influences other processes. On this account, then, implicit "assessments" of common ground emerge from a speaker's automatic sense that particular information can be treated as familiar or not within a particular context. This in turn can lead speakers to use particular forms of reference if relevant linguistic representations become sufficiently accessible via resonance within a time course that can affect planning and production. Critically, though, under this proposal audience design does not require that these representations be specifically tagged with respect to common ground, although relevant memory traces may still happen to encode partner-relevant information.

The one-bit proposal (Galati and Brennan, 2006, 2010; Brennan and Hanna, 2009) arose from the observation that, in experiments designed to distinguish the perspectives of conversational partners, common ground seems to be able to rapidly guide comprehension and planning of referring expressions when conditions differ by one or just a few wellestablished, relevant cues that in these experiments happened to be binary—for example, my partner is a native speaker of English, or not (Bortfeld and Brennan, 1997); my partner can see what I'm doing, or not (Brennan, 2005); my partner and I have the same spatial perspective, or not (Schober, 1993; Duran et al., 2011); my partner can reach the object she's talking about, or not (Hanna and Tanenhaus, 2004); my partner can see a picture of what we're discussing, or not (Lockridge and Brennan, 2002); I have talked about this with my partner before, or not (Horton and Gerrig, 2002; Metzing and Brennan, 2003; Galati and Brennan, 2006; Matthews et al., 2010); or my partner and I were interrupted before we finished discussing this, or not (Brown-Schmidt, 2009). Such contextual cues, especially if they're established as relevant through perceptual salience or having made a previous inference, can support the rapid access and use of episodic information in order for speakers to design an utterance for a particular audience (as opposed to behaving "egocentrically"), or in order for addressees to adapt the processing of a referring expression with a particular speaker in mind.

But even for the simplest of metarepresentations (e.g., she can/cannot see me talking), in order for such partner-specific information to guide processing, it must already be accessible (Horton and Gerrig, 2002); this means that the first time an inference is needed, this is likely to require additional processing time. This was demonstrated in a referential communication study (Hwang et al., 2015) in which Koreans who spoke English as a second language worked with a native English speaker to match labels that would be unpronounceable in Korean (which lacks not only any coda-final /b/ vs. /p/ contrast, but also any contrast between the vowels /æ/ and /ε/). The Korean speakers did not spontaneously produce recognizable contrasts unless they had just been primed with a similar sound by the native-English-speaking partner, or unless there was a pragmatic reason to do so, in order to make a relevant pragmatic distinction that their partners needed to do the matching task—for example, to distinguish a card labeled bib from a nearby bip. Critically, the first time they encountered their partner's pragmatic need, it took them significantly longer to initiate speaking; but when a similar pragmatic contrast (between different items) was needed after that, they were just as fast to initiate speaking as with other, baseline expressions. This evidence supports the idea that a representation of the discourse context that includes pragmatic information that has already been perceived or computed can rapidly shape referring without the need for elaborate, computationally expensive inferences (see Brennan and Hanna, 2009; Shintel and Keysar, 2009).

Thus, the one-bit account presumes a role for metarepresentations of episodes relevant to conversational contexts, permitting language use to be shaped by inferences that concern what other people might know. In particular, these inferences are most likely to occur either before a speaker formulates a referring expression (or an addressee interprets it), based on salient percepts about their physical co-presence, or at the time when a speaker or an addressee is first prompted to consider pragmatically-relevant differences, especially differences that are relatively simple and supported by a stable conversational context. At the same time, however, any metarepresentations that encode such inferences are subject to the constraints of ordinary memory; that is, they are likely to vary in strength and be schematically focused on critical features of the interactive setting. Once evoked, they may support the rapid or automatic use of partner-specific information in similar contexts [as suggested by the Hwang et al. (2015) results described above], rather than requiring additional laborious inference. For example, if an inference about common ground has already been made, or if relevant evidence is perceptually salient, then such information could be available to be used in the formulation and interpretation of referring expressions without further delay (Galati and Brennan, 2006; Brennan and Hanna, 2009). This can result in rapid and "smart" (rather than slow and laborious) adaptations of utterances to a particular partner's needs, perspective, or context.

Critically, the rapid use of partner-specific knowledge under these circumstances could readily occur via the kinds of memorybased processes described by Horton and Gerrig (2005a). Even if metarepresentations are not always deployed in language use, the number and variety of findings showing contextappropriate uses of perspective (see discussion in Brennan and Hanna, 2009; Brown-Schmidt and Hanna, 2011) demand that researchers provide a psychologically-plausible account of when and how speakers might come to consider inferences about others' knowledge. For its part, Horton and Gerrig's (2005a) memory-based account does not deny the possibility of metarepresentation. Indeed, in their description of strategic assessments of a partner's knowledge, they identified several instances in a corpus of telephone conversations in which speakers appeared to consult (or, more likely, construct) representations of what their addressees might know (e.g., "Yeah, I've got another buddy who, uh, is a Marine pilot. I'm trying to think if you had ever met this guy"). The suggestion, however, was that such activity was likely to be too computationally effortful and/or costly to provide a general account of audience design.

Even so, the primary focus of the memory-based view concerned the automatic accessibility of partner-relevant information via resonance. Much of the time, these partnerrelevant representations will be limited to episodic traces of previous encounters with others, allowing individuals to show evidence for partner-sensitivity without requiring detailed inferences about common ground. In principle, though, because resonance is a "dumb" process that works on whatever information is available in memory, there is nothing inherent about resonance as a process that would prevent it from facilitating the retrieval of representations that capture inferences about the knowledge of certain partners—as long as such information is part of the memory trace.

One of the fundamental observations about resonance as an ordinary memory process is that the types of information that become accessible via resonance are likely to be highly dependent upon features of the conversational context, both in terms of encoding strength as well as the availability of appropriate retrieval cues. Thus, certain conversational situations might not only be more likely to result in stronger memory traces for particular sources of information (Horton and Gerrig, 2005b), but might also unfold in a way that supports the direct encoding of highly constrained inferences concerning other's beliefs about that information. In particular, aspects of conversational grounding described by Clark and colleagues could under many circumstances provide the right setting for particular metarepresentational inferences to be encoded as part of the episodic trace for particular interactions (as first suggested by Clark and Marshall, 1981). For example, explicit indications that an individual has understood a particular conceptual perspective (e.g., "alright I see it, I see it" in the opening example) might be more likely to lead to the encoding of the belief that this speaker views that referent in this way. It would be important to empirically distinguish this, though, from the simpler possibility that particular kinds of feedback may just generally lead to stronger memory traces for the interaction.

One piece of evidence on this point comes from Brown-Schmidt (2012), who showed that participants generated stronger inferences about shared knowledge in situations in which they responded to direct questions from a confederate speaker, consistent with the idea that common ground is mediated via "gradient" representations. Thus, while information about simple verbal events such as "Sally called this an anchor" would, on any account, almost certainly be present in the episodic trace, processes of negotiating reference might enable information such as "Sally believes this can be conceptualized as an anchor" to (probabilistically) become part of the trace as well. The probabilistic nature of common ground is an underappreciated part of Clark and colleague's original theory, which models the strength of evidence interlocutors provide about their understanding and uptake during conversational interaction (Clark and Schaefer, 1989; Schober and Clark, 1989; Clark and Brennan, 1991; Brennan and Clark, 1996). As meanings are grounded, speakers provide metalinguistic cues as to their commitment to the content of their utterances (Smith and Clark, 1993), and hearers accurately understand and use such cues (Brennan and Williams, 1995; Swerts and Krahmer, 2005). So even though cognitive restrictions prevent individuals from encoding anything that resembles the infinite regress of mutual knowledge, they may be able to use metalinguistic cues and co-presence heuristics to estimate mutual knowledge.

Such cognitive restrictions tie in directly to the motivation for the one-bit account as proposed by Galati and Brennan (2006, 2010). Clearly, ordinary memory representations of particular social interactions cannot encode every possible inference concerning other people and potential referents as part of a simple metarepresentation. But if the conversational context supports a particular inference concerning the likely knowledge of others as relevant, then it is possible that language users may easily encode such inferences as part of the partner-specific memory trace and use it automatically in reference resolution. That is, once so-called metarepresentational information has been computed, it can be available for subsequent retrieval via ordinary resonance, as described by the memory-based model. As such, this retrieval need not be guided in the moment by explicit deliberations about another's perspective.

We wish to stress, though, that the types of representations of another's knowledge likely to be most relevant for everyday language use will most generally be quite different from the sorts of discrete, all-or-nothing inferences about mental states commonly presumed in the literature on theory of mind. That is, we believe that variation across conversational contexts, as well as within conversations over time, will shape the kinds of partner-specific information that become accessible for particular speakers as they formulate and comprehend utterances. Under these circumstances, some aspects of metarepresentational beliefs will be more immediately accessible than others, and any such knowledge is likely to be partial or schematic, depending on the nature of memory cues present in the conversational situation as well as the strengths of the underlying traces stored in memory. With repeated referring, memory traces are stronger, and so any "conceptual pact" achieved by two conversational partners to refer to a particular referent with a particular label is likely to be stronger and more easily evoked (Brennan and Clark, 1996), consistent with the probabilistic or gradient nature of common ground (Brown-Schmidt, 2012). Moreover, what might be seen as computationally expensive (such as keeping track of individual information) need not be so, if ordinary memory processes also support the binding of relevant contextual factors as part of the same representation. But, with highly similar episodes involving context switches (such as interactions with different partners), distinctions between relevant representations might become blurred, leading to further opportunities for interference leading to source-monitoring errors or egocentric mistakes.

Our converging viewpoints emphasize the fact that consideration of another's knowledge is rarely likely to be a discrete, all-or-nothing event, instead unfolding over time as cues become available in the conversational context, leading to the retrieval of partner-focused representations that are incremental and dynamically changing as new information comes online. Furthermore, we suggest that many of these inferences are likely to be simple, reusable, and highly supported by salient features of the conversational context. Once these inferences have been computed and encoded as part of the memory trace for that interaction, the resulting metarepresentations, whether schematized or not, are potentially available for retrieval via ordinary memory-based processes. As a function of ordinary memory, this retrieval will be highly dependent upon the presence of appropriate cues and can still wax and wane as the conversation proceeds.

# CONCLUSIONS

By taking seriously questions about the nature of representations to which language users have access for purposes of conversational reference, our aim has been to emphasize the extent to which such representations are constrained in a number of ways by ordinary memory, consistent with constraint-based approaches to reference and common ground (Hanna et al., 2003; Brown-Schmidt and Hanna, 2011). Such constraints are not only internal, tied to fundamental cognitive processes of attention and memory, but also external, arising from the conversational situation (including processes of grounding meanings with a partner). In particular, the issue of metarepresentation highlights key questions about the nature of the ordinary memory traces that potentially encode inferences about another's knowledge. Another person's knowledge or perspective may well have the same status in a metarepresentation as any other relevant aspect of the context in which referring takes place, or it may be supported by distinct neural circuitry (for discussion, see Brennan et al., 2010). Neuroscience has begun to explore the neurocognitive markers associated with particular types of

# REFERENCES

socially relevant capacities, including theory of mind (e.g., Ruby and Decety, 2003; Baron-Cohen et al., 2013; Hamilton et al., 2014). It remains to be seen whether representations of (or inferences about) other people's knowledge, needs, or beliefs are qualitatively different from any other contextual representations or inferences required by language use in conversation.

# AUTHOR CONTRIBUTIONS

All authors listed, have made substantial, direct and intellectual contribution to the work, and approved it for publication.

# AUTHOR NOTES

This material is based on work done while SB was serving at the National Science Foundation. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. We thank Richard Gerrig and the two reviewers for their comments on an earlier draft.

of deception. Cognition 13, 103–128. doi: 10.1016/0010-0277(83) 90004-5

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2016 Horton and Brennan. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# The Flexibility of Conceptual Pacts: Referring Expressions Dynamically Shift to Accommodate New Conceptualizations

Alyssa Ibarra1,2 \* and Michael K. Tanenhaus1,2

<sup>1</sup> Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA, <sup>2</sup> Department of Linguistics, School of Arts & Sciences, University of Rochester, Rochester, NY, USA

In a classic paper, Brennan and Clark argued that when interlocutors agree on a name for an object, they are forming a temporary agreement on how to conceptualize that object; that is, they are forming a conceptual pact. The literature on conceptual pacts has largely focused on the costs and benefits of breaking and maintaining lexical precedents, and the degree to which they might be partner-specific. The research presented here focuses on a question about conceptual pacts that has been largely neglected in the literature: To what extent are conceptual pacts specific to the local context of the interaction? If conceptual pacts are indeed temporary, then when the local context changes in ways that are accessible to participants, we would expect participants to seamlessly shift to referential expressions that reflect novel conceptualizations. Two experiments examined how referential forms change across context in collaborative, task-oriented dialog between naïve participants. In Experiment 1, names for parts of an unknown object were established in an "item" identification stage (e.g., a shape that looked like a wrench was called "the wrench"). In a second "build" stage, that name was often supplanted by an object-oriented name, e.g., the "leg." These changes happened abruptly and without negotiation. In Experiment 2, interlocutors manipulated clip art and more abstract tangram pictures in a "slider" puzzle to arrange the objects into a target configuration. On some trials moving an object revealed a picture that could be construed as a contrast competitor, e.g., a clip art picture of a camel after "the camel" had been negotiated as a name for a tangram shape, or vice versa. As would be expected, modification rates increased when a potential contrast was revealed. More strikingly, the degree to which a name had been negotiated or the frequency with which it had been used did not affect the likelihood that the revealed shape would be considered as a potential contrast. We find little evidence that names that are introduced as part of a conceptual pact persist when either the task goals or informational needs change. Rather, conceptual pacts are fluid temporary agreements.

Keywords: referential expressions, conceptual pacts, entrenchment, targeted language game, interactive conversation

Edited by:

Albert Gatt, University of Malta, Malta

#### Reviewed by:

Laura Gonnerman, McGill University, Canada Paula Rubio-Fernández, University of Oslo, Norway

\*Correspondence: Alyssa Ibarra<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Language Sciences, a section of the journal Frontiers in Psychology

Received: 10 September 2015 Accepted: 05 April 2016 Published: 25 April 2016

#### Citation:

Ibarra A and Tanenhaus MK (2016) The Flexibility of Conceptual Pacts: Referring Expressions Dynamically Shift to Accommodate New Conceptualizations. Front. Psychol. 7:561. doi: 10.3389/fpsyg.2016.00561

# INTRODUCTION

fpsyg-07-00561 April 25, 2016 Time: 14:53 # 2

There is a many-to-many mapping between names and potential referents. A picture of a Bernese Mountain Dog could be referred to as "the dog", "the Bernese Mountain Dog," "the Berner," etc. Furthermore, names can be assigned on the basis of the properties of the object (e.g., "the brown dog"), assigned with respect to a particular referential domain (e.g., "the big dog" when there is a small one as well), or assigned with respect to a referential domain that is tied to a local goal. For example, when completing a jigsaw puzzle, "try the red piece," might be uttered—and easily understood—in a collaborative task, when there are several pieces that might fit and several other red pieces that are clearly the wrong size and shape (Brown-Schmidt and Tanenhaus, 2008). A central question, then, in both reference generation and comprehension is how interlocutors choose a specific referential expression and then modify its use as a discourse unfolds.

In a classic paper, Brennan and Clark (1996) introduced the notion of a conceptual pact. Building on the foundation established by Clark and Wilkes-Gibbs (1986) and Isaacs and Clark (1987) in developing the collaborative model of conversation, Brennan and Clark argued against what they termed "a historical" accounts of the generation of referring expressions. They proposed that when participants agree upon a name, that is when the name has been grounded, they are making a temporary agreement about how to conceptualize that object. The aspect of conceptual pacts that has received the most attention in recent years is the claim that conceptual pacts are partner-specific. For example, there is an ongoing debate about how and when the use of a particular name for an object will affect processing, specifically when an established name (a maintained precedent) or a different name (a broken precedent) is used by the same partner or by a different partner (see Kronmüller and Barr, 2015 for a recent review and meta-analysis).

The current research focuses on an important aspect of conceptual pacts that has been largely ignored in the literature. In comparing their proposal with pioneering work by Carroll (1980, also see Carroll, 1985), Brennan and Clark noted that a defining characteristic of their model is that conceptual pacts are temporary and adaptable. They argued that participants can modify their utterances abruptly, that is without negotiation in response to changing goals and informational needs. Thus when the interlocutors' goals change or when the informational demands of the local context change, then the pressure to adhere to a conceptual pact might be relatively weak. If that is the case, then elucidating these factors will be crucial to developing robust theories of reference generation and understanding. Here we ask (1) whether interlocutors do indeed abruptly change their referential expressions–in particular negotiated names– when either the goals or informational demands change; and (2) whether frequent use of a name in a conceptual pact causes the name to become entrenched, that is resistant to being changed.

Given the focus in the literature on the benefits of maintaining precedents and the costs of breaking precedents, Brennan and Clark's (1996) evidence for conceptual pacts becoming entrenched is arguably quite weak. They found that when interlocutors used a subordinate-level name because a picture was introduced in the context of another member of the same category (e.g., a collie in the context of two dogs), they often continued to use that name rather than the more basic-level name (e.g., "dog"). This can be viewed as a form of over-modification, which is quite common (see Pogue et al., 2016).

Conversely, the evidence for the flexibility of conceptual pacts is also relatively weak. Brennan and Clark (1996) found that after using a basic-level name, such as "shoe," interlocutors would switch to a subordinate level category, e.g., "penny loafer" when confronted by a situation in which there was more than one type of shoe. In this situation each of the potential referents would be an equally good fit to the previous referential description of "shoe." Moreover, changing the name from a basic-level category name to a subordinate-level name does not require a major shift in conceptualization.

If a grounded name reflects a temporary agreement to conceptualize an object in a particular way with respect to a particular set of goals and informational needs, then when the goals or informational needs change, participants will no longer seek to use previously grounded referring expressions. The current research was designed to test this claim using stronger manipulations than those used by Brennan and Clark (1996). In Experiment 1, we introduce a change in the goal structure of a collaborative task that could potentially trigger a bigger shift in conceptualization in order to see whether or speakers will make non-negotiated, abrupt changes in their use of a referring expression. In Experiment 2 we introduce a change in the referential context by introducing a new object that could be treated as contrastive or not, depending on whether participants choose to maintain a previous conceptual pact.

Both experiments use "targeted language games" (Brown-Schmidt and Tanenhaus, 2008; Tanenhaus and Brown-Schmidt, 2008) with task-oriented dialog. In most experimental work on naming, the referential domain depends primarily on a fixed set of potential referents, with little or no collaboration and minimal task constraints (e.g., Nadig and Sedivy, 2002; Sedivy, 2003; Brown-Schmidt and Tanenhaus, 2006; Engelhardt et al., 2006; Brown-Schmidt and Konopka, 2008). Thus there are no changes in either the goals or informational demands that might lead participants to abandon previously established conceptual pacts.

In task-oriented dialog, however, interlocutors work together to establish a given name in order to uniquely identify a referent with respect to goals, which might be hierarchically arranged. Therefore the language is unscripted and the referential domains are likely to be more fluid than in studies using other tasks.

An example of how task constraints and local goals can modulate referential domains comes from a study by Brown-Schmidt and Tanenhaus (2008). In their study, two participants who could not see one another collaborated to match place pieces on their respective DuploTM pegged boards such that the boards would match. Participants had identical boards that were divided into several sub-regions defined by cardboard borders. Additionally, participants had stickers covering the pegs on the board indicating the type of block (e.g., color

and shape) that was to be placed in that particular location; where one participant had a sticker, the other participant's board was blank. Brown-Schmidt and Tanenhaus analyzed utterances in which one of the participants referred to a block when there was a potential competitor referent in the same subregion (e.g., a red, vertical block, when there was another red block, like a red horizontal block). Whereas one might expect speakers to use referential expressions that would take into account all of the potential referents, more than 50% of there referential descriptions were "under-informative," For example, the speaker might say "Put it above the red block." Surprisingly, these potentially ambiguous referring expressions were not confusing to the addressee. When the task constraints were factored in, these "under-informative" referring expressions did in fact uniquely identify a single block, (e.g., only one of the red blocks had enough space above it to put another object). The goal of placing blocks in particular configurations thus restricted the referential domain to only those that fit.

We explore two hypotheses about the context-dependence of conceptual pacts. The first hypothesis is that a conceptual pact is specific to a task goal. The strongest form of this hypothesis is that when the goal changes, interlocutors will neither seek to maintain, nor avoid breaking, lexical precedents. The second hypothesis is that participants will no longer be bound by prior conceptual pacts whenever there is a change in the potential informational demands. We assess this by introducing new objects that could be named in different ways to see if participants seek to generate a referential description that would allow them to maintain a lexical precedent.

# EXPERIMENT 1: CONCEPTUAL PACTS AMID SHIFTING GOALS

In Experiment 1 we created a situation in which two interlocutors who could not see each other's work areas collaborated to build a three-dimensional puzzle of an animal. The partners' task was divided into two phases. In the first phase, participants retrieved and named relevant puzzle pieces (abstract shapes) from a larger set using instructional cards as a guide. Each card showed a picture of an object that would be needed later. Participants had no knowledge of the end goal of the puzzle. In the second phase, participants used those pieces to build the animal puzzle. We focused on whether the shift in goal from picking out abstract objects from a set to the assembly of an animal would predict a change in references to objects with previously grounded referring expressions. We asked whether an abstract object referred to by a grounded name (e.g., the wrench) would be referred to by a different, object-based name (e.g., the leg) when the goal is shifted, and if so, whether the change in name would need to be negotiated or even commented on by the interlocutors (e.g., "the wrench is a leg"). We also hoped to find cases where that piece did not fit (e.g., the piece referred to as "the leg" wouldn't fit) in order to see whether participants would then reuse the negotiated name.

# Materials and Methods

We created a turn-taking language task designed to elicit repeated reference to a specific set of objects. The design is a subset of a larger paradigm used in studies assessing linguistic convergence and miscommunication (Roche et al., 2013; Paxton et al., 2014). The participants' overall task was to build threedimensional puzzles using pictorial instruction cards. The task constrained both the objects requiring linguistic reference and the order in which they were to be manipulated, but participants were otherwise able to speak freely. In addition, a barrier was introduced so that there was no shared visual space, thereby necessitating that using spoken language was the primary means of communication (e.g., shifts in gaze or point could not be used as cues). Turns were implemented rigidly, as instructions were staggered across the two instruction stacks, one for each participant and both of which made up the full set of instructions. These were ordered to ensure successful alternation of turns.

Stimuli included three BlocoTM animal puzzles, consisting of a grasshopper, lion and lizard (see **Figure 1** for final product) and order of objects was counterbalanced across participants. The number of instructions varied between the objects (total range: 17–32 instruction cards; see **Table 1** for a breakdown; see **Figure 2** for sample instruction cards).

TABLE 1 | Number of instruction cards for each animal, total and by phase.

FIGURE 2 | Sample item phase instruction card (left) and build phase instruction card (right) for lizard.

#### Task: Phase Structure

fpsyg-07-00561 April 25, 2016 Time: 14:53 # 4

To create a situation in which repeated reference to the same objects would occur across two different contexts by virtue of a shift in task, separate phases were introduced: the item phase and the build phase. In the item phase, participants picked out the individual pieces needed to build the object. Both participants were given identical sets of pieces in a bin. During a turn, each participant would pick out the piece on her card from her bin and then describe the object so that her partner could do the same. Instructions alternated until the proper subset of items had been selected. Note that the identity of the object to be built was not given until the item phase was complete.

Once the item phase was complete and the participants had matching pieces on their workspaces, the build phase began. During the build phase, participants also alternated instructions, with each instruction card describing how to build a combination of those pieces obtained in the item phase; these were ordered and staggered to establish turn taking. Crucially, these pieces were to be combined and then added onto a pre-constructed object—an unfinished animal body. The unfinished animal body was presented at the beginning of the build phase in order to emphasize the shift in task. In the item phase, we expected participants were likely to uniquely identify pieces relative to the set of alternatives in the bin. In the build phase, we expected that participants would refer to pieces relative to their relationship to the build-object, especially once its structure began to emerge.

For both phases, participants were video-recorded and the audio was extracted to fully transcribe the participants' dialog. Transcriptions were then coded with the following annotations.

#### Annotations

Discourse features:

Features of referential expression:

Fine-grained: classed individually as "mhm," "yup," "yeah," "yes," "okay," "alright."

Course-grained: classed as "mhm," "yup," "yeah," "yes," "okay," "alright."

#### Outcome Variables

The variable of interest was a change of a referential form, as realized in the repeated reference of any given puzzle piece. This was operationalized as a change in the head noun of a referring expression.

Secondarily, the specific type of change was explored, with any given change categorized as either a negotiated change or an abrupt change. We operationalized negotiated changes as those referential expressions whose changed form was introduced obliquely in prior discourse but not as the head noun. Because these often were the complements of constructions such as "looks like a wrench," this was the only linguistic construction used to code negotiated changes. This was a simplification, as changes in form might be negotiated in discourse in a different way, however, for present purposes, we restricted negotiated instances to the "like-complement" cases. Abrupt changes were taken to be any change in head noun whose new form was not given in previous discourse. See **Figure 3** for an excerpted transcript of participants who call a piece "the wrench" repeatedly in the item phase but shift to calling it "the leg" without overt negotiation.

#### Participants

Nine pairs of undergraduates participated from the University of Rochester (N = 18). All participants were native speakers of American English with normal to corrected vision. None reported speech or hearing impairments. This study was carried out in accordance with the Research Subjects Review Board (RSRB) at the University of Rochester. All participants gave written informed consent in accordance with the Declaration of Helsinki and were debriefed and offered a copy of the consent form upon completion of the experiment.

# Results

#### Descriptive Data

The following description and analysis includes data from the nine pairs of participants. The dataset consisted of a total of 1,776 turns containing referential expressions. These referential expressions were hand-annotated and then coded for groundedness. A referential expression was coded as grounded if it was followed by any of the following agreement markers: mhm, yup, yeah, yes, okay, or alright. All other referential expressions were coded as not grounded. A non-grounded expression, if taken to be a proposal for a name that has not been accepted, is likely to undergo changes until a name is established. This was not a change in form that we were interested in, since they would not be broken pacts. Therefore, we restricted our dataset to grounded expressions. These made up the subset of data that was used for the following analyses. **Table 2** presents a breakdown of the number of grounded and changed referential expressions. Note that when looking at head noun changes generally, they were quite evenly distributed across groundedness: 50.58% of head noun changes were grounded. Thus changes were not primarily the result of a pact not having been formed in the first place.

#### Analyses

To assess whether a context shift predicted a change of form, we used a generalized linear mixed model including random

TABLE 2 | Total number of referring expressions.

Note: A subset of the total were grounded, and a subset of the grounded expressions underwent a change in form (nested values).

intercepts only, with presence of head noun change as the outcome variable, phase as predictor and pair as a random effect. The model showed that build phase significantly predicts a change in form (β = 0.86, SE = 0.13, p < 0.001). **Figure 4** presents the proportion of changes in the two phases.

A second generalized linear model was used to assess how changes were realized across a task-goal shift. We included random intercepts and the model contained phase as the outcome variable, change type (either negotiated or abrupt) as the predictor and pair was the random effect. The decision to reverse the directionality of the model from the first was motivated by the fact that the categories of change type were ad hoc categories meant to provide a finer-grained description of a change in form. Thus, we wanted to assess whether occurrences of a particular type of change could predict whether the pair was in the item or build phase. Indeed, the model shows that an occurrence of an abrupt change increases the likelihood that a pair is in the build phase (β = 0.975, SE = 0.23, p < 0.001). See **Figure 5** for the proportions of abrupt changes for each phase. Although there were not sufficient trials for a statistical analysis, we observed a striking phenomenon that further highlights the context-dependence of names. On 16 trials, one of which is

illustrated in **Figure 3**, participants made an abrupt change from a negotiated name (e.g., wrench) to an object-oriented name (legs) and then found the piece would not fit. On each of these trials, participants then reverted to the name used during the item-phase (e.g., wrench). This illustrates that participants can shift seamlessly between different names, which reflect different conceptualizations of the objects tied to different task goals.

### Discussion

In Experiment 1, changes in the context were instantiated by a shift in task goals, i.e., the shift from the item phase to the

build phase. This allowed us to determine whether a conceptual pact that was established when the participants had a particular goal would need to be renegotiated when the goal changed. The answer was clearly "No," highlighting that conceptual pacts are strongly dependent on task goal. We note that an overall task goal, such as building an animal, is likely to have hierarchically organized subgoals, e.g., building a part of the animal (e.g., the face). We are assuming the conversation takes place against the backdrop of these goals as well as more local subgoals. This raises the important issue of how local task goals interface with a conversation as it unfolds. One possibility is that local goals might play a role in determining the Question Under Discussion (Roberts, 1996), but this is beyond the scope of the current paper.

In Experiment 2, we examine the extent to which a name agreed upon in a conceptual pact is entrenched when new objects are introduced that may potentially change the informational demands. First, we explore whether negotiation of a name is predicted from the properties of an object, i.e., whether it is a commonly identifiable object given the alternatives. This manipulation was important for two reasons. First, it allowed us to establish that the typical pattern for negotiated referring expressions, namely a reduction in length across repeated references would be replicated in our task. Secondly, increased negotiation for less identifiable objects would provide evidence that that object is likely to be more compatible with multiple descriptions compared to the more identifiable objects. As will become clear this property of our design creates situations in which the speaker could generate a referential expression that would allow them to maintain a lexical precedent.

# EXPERIMENT 2: CONCEPTUAL PACTS AMID EMERGENT NAMING COMPETITORS