Two experiments were conducted in a virtual reality (VR) environment in order to investigate participants' in-store visual search for bottles of wines displaying a prominent triangular shape on their label. The experimental task involved virtually moving along a wine aisle in a virtual supermarket while searching for the wine bottle on the shelf that had a different triangle on its label from the other bottles. The results of Experiment 1 revealed that the participants identified the bottle with a downward-pointing triangle on its label more rapidly than when looking for an upward-pointing triangle on the label instead. This finding replicates the downward-pointing triangle superiority (DPTS) effect, though the magnitude of this effect was more pronounced in the first as compared to the second half of the experiment, suggesting a modulating role of practice. The results of Experiment 2 revealed that the DPTS effect was also modulated by the location of the target on the shelf. Interestingly, however, the results of a follow-up survey demonstrate that the orientation of the triangle did not influence the participants' evaluation of the wine bottles. Taken together, these findings reveal how in-store the attention of consumers might be influenced by the design elements in product packaging. These results therefore suggest that shopping in a virtual supermarket might offer a practical means of assessing the shelf standout of product packaging, which has important implications for food marketing.

#### Edited by:

Anton Nijholt, University of Twente, Netherlands

#### Reviewed by:

Alan M. Wing, University of Birmingham, United Kingdom Alejandro Catala, University of Twente, Netherlands

#### \*Correspondence:

Xiaoang Wan<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Human-Media Interaction, a section of the journal Frontiers in Psychology

Received: 21 August 2017 Accepted: 29 November 2017 Published: 13 December 2017

#### Citation:

Zhao H, Huang F, Spence C and Wan X (2017) Visual Search for Wines with a Triangle on the Label in a Virtual Store. Front. Psychol. 8:2173. doi: 10.3389/fpsyg.2017.02173

Keywords: visual search, virtual reality, triangle, wine labels, DPTS effect

# INTRODUCTION

Product packaging constitutes a powerful marketing tool (see Spence, 2016, for a recent review). It allows manufacturers and marketers to deliver important information regarding the product, attract consumers' attention, and ultimately influence their evaluation of a product via various specific features, including color, shape, curvature, label, typeface, and so on (for comprehensive reviews, see Hine, 1995; Simmonds and Spence, 2017). As for food and drink purchases, consumers have their first sensory contact with the products via what they see. Visual cues also provide a dominant sense as far as the generation of product expectations are concerned (Schifferstein et al., 2013; Piqueras-Fiszman and Spence, 2015). Packaging not only affects how food and drinks are perceived at the point of sale (e.g., Becker et al., 2011; van Rompay et al., 2016), but can also influence how they are experienced at the point of consumption (Schifferstein et al., 2013; Spence, 2016).

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Over the years, many studies have been designed to examine how the attention of consumers in-store is affected by the design elements in product packaging (e.g., Schoormans and Robben, 1997; Underwood et al., 2001; Pieters et al., 2010; Otterbring et al., 2013). In the store setting, of course, each and every product on the shelves competes for the consumer's limited visual attention. Nevertheless, according to Hoyer (1984), it only takes a few seconds for a customer to make their decisions when buying fastmoving consumer goods (FMCGs). Perhaps unsurprisingly, it has been argued that the more attention a customer pays to a product, the greater the likelihood that they will choose it (see Orquin and Loose, 2013, for a comprehensive review). Compared to changing the appearance of the product itself, changing the packaging and labeling of the product may well constitute a more costefficient, but no less effective means of attracting the attention of customers.

Purchasing wine constitutes a particular challenge (relative to other product categories). In fact, searching for a specific brand/vintage in the wine aisle can be both difficult and challenging, given the often complex and ever-changing range on products one finds for sale on the wine shelves. The appearance of the bottles, especially the design of the wine labels, might be expected to influence a consumer's liking of, or preference for, the product (Cutler, 2006; Boudreaux and Palmer, 2007; Labroo et al., 2008; De Mello and Pires, 2009; Westerman et al., 2013; Gmuer et al., 2015). What is more, it can also guide customers' attention in searching for the product presented on the store shelves (Thomas and Pickering, 2003; Elliot and Barth, 2012).1

The visual search task has been one of the most common experimental paradigms used to study attention (e.g., Nothdurft, 1999; Hopf et al., 2000). In visual search, certain shapes are easier to find than others. For example, a circle with a straight line like a "Q" is easier to find amongst regular circles than vice versa (Treisman and Souther, 1985; Treisman and Gormican, 1988). Such research show that it is easier to search for the presence of a feature than for its absence. Searching for a downwardpointing triangle among upward-pointing distractor triangles has also been shown to be faster than vice versa (Larson et al., 2007). The latter effect is known as the Downward-Pointing Triangle Superiority (DPTS) effect. The existence of this effect has been attributed to the fact that downward-pointing triangles are more likely to convey threat-related information than are upwardpointing triangles. It has been suggested that this is because they resemble angry faces in which the muscles are pulling down to form a "V" shape (Larson et al., 2012; Toet and Tak, 2013), and therefore capture attention more readily than do neutral stimuli such as upward-pointing triangles (see Larson et al., 2007, 2012; Watson et al., 2012).

It is widely acknowledged that the rapid detection of threatrelated stimuli conveys an evolutionary advantage and is thus vital to human survival. The "Shape of Threat" account of the DPTS effect is also supported by neuroscience evidence showing that viewing downward-pointing triangles increases the neural response seen in the amygdala (Larson et al., 2009). This neural structure plays a crucial role in emotional processing, especially in the detection of potential threats (e.g., Morris et al., 1996; LeDoux, 2000).

It is important to note, however, that this threat-related explanation of the DPTS effect might not easily be used to account for the comparable pattern of results documented with non-threatening images of triangular-shaped foods and pizza packaging (Shen et al., 2015). Considering the global precedence in visual perception (e.g., Navon, 1977; Pomerantz, 1983), one possibility is that the global outline shape of the stimuli (i.e., the downward-pointing triangle which could be threat-related) might be processed before the meaning of the stimuli (food or food packaging which are not threat-related). Nevertheless, the DPTS effect has also emerged with wine bottles that have triangular shapes on their labels whereby the triangles were only local features (Zhao et al., 2016). What is more, compared to foods presented in triangular form, or food packaging which is often stacked horizontally, the wine labels attached to the front of wine bottles and typically presented vertically. This means that the triangles appearing on the wine labels may actually point downward or upward in both daily life and experimental research (see Shen et al., 2015, for an example of a downward-pointing triangle actually being used in a commercially successful wine label). By contrast, foods or food packaging in triangular form usually point toward or away from the observer in daily life, but they were presented vertically in Shen et al.'s (2015) experiments. Nevertheless, it remains unclear whether a similar DPTS effect would also emerge with consumers in a store setting. Here it is important to note that conducting field studies (e.g., in a supermarket) can be both expensive and time-consuming. By contrast, using virtual reality (VR) to simulate a store experience offers a potentially efficient and effective means of keeping the costs of research down and can be argued to increase the external validity of one's research relative to other computer-monitor based lab experiments.

A computer-mediated three-dimensional environment can be created in VR in which users can experience a sense of presence, and which provides realistic visual scenes, sense of movement, and so on (e.g., Biocca, 1992; Steuer, 1992; though see also Gallace et al., 2012). In particular, VR can simulate naturalistic environments via an immersive human–computer interaction (Berneburg, 2007; Lee and Chung, 2008; Bressoud, 2013). It can also be used to efficiently deliver realistic food cues to elicit craving (at least as indexed by self-report and salivation) just like actual food does (Ledoux et al., 2013; though see also Spence, 2011). Intriguingly, virtual stores can elicit similar consumer choice of food products such as milk and cookies as those that have been documented in a physical store (van Herpen et al., 2016; see also Waterlander et al., 2015), and have been used to examine purchases of alcoholic drinks, such as beer (Bigné et al., 2016).

In the present study, we wanted to examine whether the DPTS effect would emerge in the visual search for bottles of wine in a virtual supermarket. Specifically, three questions were addressed by the research reported here: First, is the visual search for a wine bottle with a downward-pointing triangle on its label in a virtual supermarket significantly more efficient (that is, faster

1Here it is worth noting that many wine producers also use the weight of the bottle to try and convey product quality too (see Piqueras-Fiszman and Spence, 2012).

and/or more accurate) than when the target bottle had a triangle point upward? Second, considering that products presented on the top shelf typically receive more attention than those placed lower down (e.g., Chandon et al., 2009; though, see van Herpen et al., 2016, for the opposite pattern in consumers' choice of milk and cookies), we also examined whether the DPTS effect in the visual search for wines might be modulated by the position of the target bottle on the store shelf. Third, how does the orientation of the triangular shape on the wine label influence people's rating of the bottles themselves, and is their preference for the item related to the efficiency of their visual search performance for it?

# EXPERIMENT 1

Experiment 1 attempted to replicate Zhao et al.'s (2016) recent results using pictures of wine shelves in a virtual supermarket. The participants were invited to come to a psychology laboratory that was equipped with a head-mounted display (HMD) VR system, and to immerse themselves in a virtual supermarket to perform the visual search in a wine aisle.

# Methods

#### Participants

Twenty-four Chinese participants (mean age = 21.08 ± 1.95 years, ranging from 18 to 27 years; 12 females and 12 males) were recruited from the subject pool of the Applied Cognition Laboratory of Tsinghua University, Beijing, China.2 All of the participants reported having normal or corrected-to-normal vision. Each participant was compensated with 35 Chinese Yuan (CNY) for taking part in the study. The present study was approved by the ethics committee of the Psychology Department of Tsinghua University, and conformed to the ethical standards for conducting research established by the American Psychological Association.

#### Apparatus and Virtual Displays

Both of the experiments reported in the present study were conducted at the VR Laboratory at the Department of Psychology of Tsinghua University. An NVIS nVisor SX60 HMD VR system was used, which produces stereoscopic imagery at 60 frames per second per eye. The display for each eye had a resolution of 1280 (horizontal) × 1024 (vertical) pixels, and the optical field for each eye was 44◦ (horizontal) × 35◦ (vertical). **Figure 1** shows the screenshots from the left eye of the HMD. The participants used a Logitech F710 wireless gamepad to interact with the virtual environment, while the Vizard software (by WorldViz) was used to conduct the experiment and record the data.

The immersive virtual environment (IVE) in this study consisted of a supermarket created with the Autodesk 3Ds Max 2009 software. The whole supermarket was 20 m long, 15 m wide, and 5 m high, though the participants in the present study

were only allowed to move along one of the aisles (7.6 m long and 1.6 m wide) with 4-shelf grayish white rack on both sides. There were a total of four racks on each side of the aisle, each of which consisted of four shelves with punch backboard. Each rack had a depth of 0.45 m. The base of the top, second, third, and bottom shelves were 1.77, 1.36, 0.94, and 0.5 m away from the ground, respectively. As can be seen in **Figure 1**, all of the bottles were presented on the top shelf. In order to make sure that all of the participants were able to see the same displays, the eye height in the virtual supermarket was set to 1.85 m regardless of the actual height of the participants. Therefore, when the participants looked at the rack, they were able to see all of the bottles (approximately 1.65 m away from where they were standing), without having to lift their heads.

Within each display, there were a total of 8 bottles, 0.15 m apart from each other. As can be seen in **Figure 2**, the bottles were made of clear glass in order to reveal the color of the liquid within (approximately crimson, beige, brown, or clear), implying that the bottles contained red wine (0.41 m in height and 0.09 m in diameter), white wine (0.41 m in height and 0.09 m in diameter), whiskey (0.32 m in height and 0.11 m in diameter), or Chinese baijiu3 (0.27 m in height and 0.07 m in diameter), respectively. Each bottle had a downward- or upward-pointing triangle on its label, with fictional brand names. All of the bottles in each display presented the same wine, though one of the bottles was randomly determined to have a different label from the others. In other words, all of the trials in this experiment were the target-present trials.

In this virtual supermarket, the participants pressed a button on the gamepad in order to move along the aisle at a constant speed of 1.5 m/s, while keeping their bodies physically still.

2Zhao et al. (2016) used a within-participants design with a sample of 20 participants in their Experiment 1, and documented a significant DPTS effect of 164 ms (SD = 131 ms) with triangles on wine labels. While we set the Type I error probability of the present study at 0.05, we need at least nine participants (resulting in nine pairs of data) to obtain a power of 0.9 for the present study.

3Note that baijiu is a traditional Chinese distilled alcohol which has a clear appearance. It is often referred to as "Chinese liquor/spirits" in English or "white wine" in Chinese (see Wan et al., 2015).

By contrast, they were instructed to physically turn their body around when needed. Thus, the information regarding transition was purely based on optic flow, whereas the information regarding rotation was based on both optic flow and body senses. Such a combination of cues has been shown to efficiently provide self-motion information to the participants (e.g., Wan et al., 2010, 2012).

#### Design and Procedure

The experimental task involved trying to find the bottle with a label that was different from the others, i.e., finding the one having a downward-pointing triangle on its label among others having upward-pointing triangles, or vice versa. After finishing a practice block of eight trials, each participant completed eight blocks of eight trials each. Each type of bottle was shown in 16 trials, with half with a downward-pointing target and an upwardpointing target in the remainder. All of the trials were mixed and presented in a random order. Within each trial, the location of the target was randomly determined.

At the beginning of each experimental block, the participants stood at one end of the aisle, adjacent to the rack on their left and facing the other end of the aisle. They were instructed to press a button on the gamepad to move forward along the aisle until a red arrow pointing to the right appeared in front of them, which instructed them to turn around to face the rack on their right where a display of eight bottles was presented. The red arrow disappeared when facing the display, and then a blue rod extending horizontally from their body to the display appeared (see **Figure 1** for an illustration). When the participants were searching for the target, they rotated their head to direct the blue rod to point to the target, and then pressed another button on the gamepad to pick it up. If they made a correct response, the target bottle disappeared; if not, a red cross appeared, and a short beep was played via the helmet they were wearing in order to alert them of the mistake. After that, a red arrow pointing to the left appeared to instruct them to turn left to face the aisle and then to proceed to the next trial. This procedure was repeated until the participants reached the end of the aisle where they were instructed to turn around to face the end of the aisle from which they had started and now had to perform the task with the displays on their left. When they arrived back at the start of the aisle, which means they had finished a total of eight trials, the block ended.

#### Data Recording

During each trial, the participant's response (to select the target) was recorded. We used two dependent variables to assess the participants' visual search performance, including: (1) the responses times (namely the RTs), consisting of the response latencies (from seeing the display to starting moving), the time durations to start moving to pointing the target, and the time durations to press a button on the game pad to confirm the selection, and (2) accuracy to indicate whether the target was correctly selected.

# Results and Discussion

In this experiment, the mean accuracy of participants' responses was high (95.9%). RT data lower than 150 ms or in excess of three standard deviation of the group mean were excluded from the subsequent data analyses, which resulted in 0.91% of the data being discarded. Preliminary analyses revealed that searching for a downward-pointing target (4282 ms, 95.2%) was comparable to searching for an upward-pointing one (4402 ms, 96.5%), both Fs < 2.13, ps > 0.15. However, when we further broke down the data, we noticed that the participants' responses speeded-up as a function of the number of experimental blocks that they had completed. Therefore, we divided the eight experimental blocks into two halves. Mean RTs calculated based on correct trials (in which the participants correctly selected the target) and accuracy data for each type of target are shown in **Figure 3**.

The 2 (Target Orientation: downward- or upwardpointing) × 2 (Block Order: the first or last 4 blocks) Analyses of Variances (ANOVAs) on the RT and accuracy data revealed a significant main effect of Block Order on the RTs, F(1,23) = 13.92, p < 0.01, η 2 p = 0.38, but not on the accuracy data, F(1,23) = 0.03, p = 0.87. These results suggested that the participants responded more rapidly in the last four blocks (4232 ms, 95.9%) than in the first four blocks (4709 ms, 96.0%) with comparable accuracy in the two halves of the study. The results also revealed a marginally significant main effect on the RTs, F(1,23) = 3.14, p = 0.09, η 2 p = 0.12, that was qualified by a significant interaction between Target Type and Block Order, F(1,23) = 5.29, p = 0.03, η 2 p = 0.19. Post hoc pairwise comparisons revealed that in the first four blocks, searching for a downward-pointing target (4523 ms, 94.7%) was faster than searching for an upward-pointing target (4894 ms, 97.4%), t(23) = 2.16, p = 0.04, Cohen's d = 0.45, with comparable accuracy, t(23) = 1.26, p = 0.22, thus indicating a significant DPTS effect of 371 ms. By contrast, in the last four blocks, searching for a downward-pointing target (4228 ms, 95.4%) was comparable to searching for an upward-pointing target (4237 ms, 96.3%), both ts < 1.26, ps > 0.22.

Considering the high (i.e., near-ceiling) accuracy in this experiment, we also log-transformed the accuracy data and performed the Target Orientation × Block Order ANOVA. None of the main or interaction effects were significant, all Fs < 1.90, ps > 0.18.

Taken together, these results revealed that the DPTS effect emerged when the participants started to search for a wine bottle having a triangle in a different orientation from the others on the front label, though such an effect might be eliminated by the practice effect when the task was performed repeatedly. The emergence of the DPTS effect in the visual search for wine labels in a virtual supermarket is consistent with what has been documented in similar search performed with pictures of store shelves previously (Zhao et al., 2016), thus suggesting that wine labels, as a local packaging feature, can effectively attract consumers' attention in visual search for a product presented on the store shelves (Thomas and Pickering, 2003; Elliot and Barth, 2012). However, the attenuation of the DPTS effect with practice was not unusual given the published visual search literature (e.g., see Hoffman et al., 1983; Hock et al., 1985; Menneer et al., 2012).

It should be noted that all 8 of the bottles within each display were presented on the top shelf on one side of the aisle in our first experiment. This is relevant given that previous research has revealed that the products presented on the top shelf receive more attention than those at the bottom (Chandon et al., 2009; see also Sunaga et al., 2016). Thus, it remains unclear whether the DPTS effect observed with the bottles presented on the top shelf would also be generalized to products that happened to be presented on other shelves. Nevertheless, we were worried that it might introduce too many confounding factors (e.g., head movement, and display size, etc.) to present the bottles on the bottom shelf in the virtual supermarket. Thus, in Experiment 2, we chose to present the eight bottles within each display on two adjacent shelves, and examine the influence of target position. What is more, we also presented the displays on both sides of the aisle to simulate a somewhat more natural shopping situation. Thus far, it remains unclear whether the orientation of the triangle on the wine labels influence consumers' subjective ratings of and/or preference on the bottles of liquid. In order to address this issue, we also had the participants rate the stimuli after the visual search task of Experiment 2.

## EXPERIMENT 2

#### Methods

Twenty-four Chinese participants (mean age = 21.04 ± 2.96 years, ranging from 18 to 28 years; 12 females and 12 males) were recruited from the same subject pool as in Experiment 1. None of the participants had taken part in Experiment 1. All aspects of the methods of this experiment were identical to those reported in Experiment 1 with the following exceptions.

First, in order to examine the position effect, the eight bottles of liquid were presented on two adjacent shelves (i.e., the top and second shelves), which we refer to as the upper and lower shelves, respectively. Thus, there were 4 bottles on each shelf, 0.2 m apart from each other. In order to make sure that all of the participants saw the same displays across the two adjacent shelves, the eye height in this experiment was set to 1.72 m, which was lower than that in Experiment 1. Thus, a 2 (Target Orientation: downwardor upward-pointing) × 2 (Target Location: the upper or lower shelf) within-participants experimental design was used. In order to more naturally simulate an everyday shopping experience, we also used a virtual hand to replace the blue rod in Experiment 1 (see **Figure 4** for an illustration).

Second, in this experiment, the bottles were presented on both sides of the aisle. At the beginning of each block, the participants stood at the center of the aisle, and then moved forward to respond to the displays on their right. When they had finished with all the displays on the right and arrived at the end of the aisle, they were instructed to turn around in order to be able to respond to all the displays on the other side. Therefore, the shelf displays were always on the participant's right side in this experiment. As the participants stood at the center of the aisle, the displays were approximately 1.1 m away from where they were standing.

Third, in order to eliminate or at least reduce the practice effect observed in Experiment 1, the task in this experiment was designed to be somewhat more complicated. Specifically, the participants first had to press a button on the gamepad to identify whether the target (which had a different wine labels from all seven other bottles) was on the upper or lower shelf, then to direct the virtual hand (by turning the head) to choose the target on the selected shelf. The participant's responses to identify the shelf where the target was located and to choose the target were both recorded. Therefore, a total of four dependent variables were used to assess the participants visual search performance, including: (1) the RTs of identification (from seeing the display to pressing a button on the game pad to indicate where the target was located on the upper or lower shelf; (2) accuracy to indicate whether the shelf where target was located was correctly identified; (3) the RTs of choosing the target, consisting of response latencies, the time durations to start moving to pointing to the target, and the time durations to press a button on the game pad to confirm the selection; and (4) accuracy to indicate whether the target was correctly chosen.

Last but by no means the least, after finishing the visual search task, all of the participants completed a survey at Unipark4 in order to rate the bottles (with a downward- or upward-pointing triangle in its label) presented in the visual search task as well as simple shapes of triangle (pointing downward or upward). During each trial, a picture was shown, and the participants rated the picture on the same 7-point scales as Shen et al. (2015) used, including (1) valence scale (ranging from very unpleasant to very pleasant), (2) arousal scale (ranging from very relaxing to very exciting), (3) familiarity scale (ranging from extremely unfamiliar to extremely familiar), and (4) liking scale (ranging from extreme dislike to extreme liking). At the end of the experiment, all of the participants were also asked how often they consumed and purchased alcoholic drinks in daily life (i.e., never, occasionally, sometimes, or often).

#### Results

#### The DPTS Effect in the Visual Search Task

In this experiment, the mean accuracy of participants' responses to identify whether the target was located on the upper or lower

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4www.unipark.de
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shelf was high (98.4% correct). After the participants had made a correct identification response, they had a high accuracy of 97.0% in responses of choosing the target. RT data (for both identification and choosing) lower than 150 ms or in excess of three standard deviation of the group means were excluded from the subsequent data analyses. This resulted in 2.7 and 2.4% of the data being discarded, respectively. Mean RTs calculated based on correct trials and accuracy data for each type of target are shown in **Figure 5**.

Considering the observed influence of practice on the DPTS effect reported in Experiment 1, a repeated-measures ANOVA – 2 (Target Orientation: downward- or upward-pointing) × 2 (Target Location: the upper or lower shelf) × 2 (Block Order: the first or last 4 blocks) was first performed on the data of Experiment 2. The results revealed a significant main effect of Block Order on the identification RTs, F(1,23) = 18.56, p < 0.001, η 2 p = 0.45, suggesting that the participants identified the shelf where the target was located more rapidly during the last four blocks (2595 ms) than during the first four blocks (2931 ms). Nevertheless, none of other main effects of Block Order or any interaction terms between Block Order and Target Orientation/Location was significant, all Fs < 2.93, ps > 0.10. Therefore, Block Order was not included in the following analyses.

Next, 2 (Target Orientation: downward- or upwardpointing) × 2 (Target Location: the upper or lower shelf) repeated-measures ANOVAs were performed on the RT and accuracy data of the identification responses. The results revealed a significant main effect of Target Location on the RTs, F(1,23) = 26.20, p < 0.001, η 2 p = 0.53, thus suggesting that the participants identified the target more rapidly when it was presented on the upper shelf (2516 ms) than when it was presented on the lower shelf (3018 ms). None of other main or interaction effects was significant, all Fs < 0.80, ps > 0.38, indicative of the absence of the DPTS effect in the identification responses.

After that, analogous analyses were performed on the RT and accuracy data of the choosing responses. The results revealed a significant main effect of Target Orientation on the RTs, F(1,23) = 7.00, p = 0.01, η 2 p = 0.23, and on the accuracy data, F(1,23) = 5.25, p = 0.03, η 2 p = 0.19. However, these main effects were qualified by the marginally significant interaction terms between Target Orientation and Target Location on the RTs, F(1,23) = 3.90, p = 0.06, η 2 p = 0.15, and on the accuracy data, F(1,23) = 4.01, p = 0.06, η 2 p = 0.15. What is more, there was also a significant main effect of Target Location on the accuracy data, F(1,23) = 4.26, p = 0.05, η 2 p = 0.16, but not on the RTs, F(1,23) = 0.60, p = 0.45. In order to interpret these interaction terms, the data were further broken down and pairwise comparisons were performed for each target location. The results revealed that choosing a downward-pointing target on the upper shelf (2223 ms, 96.1%) was faster than choosing an upward-pointing target on the same shelf (2492 ms, 96.3%), t(23) = 3.68, p < 0.01, Cohen's d = 0.76, with comparable accuracy, t(23) = 0.13, p = 0.90, indicative of a significant DPTS effect of 269 ms. By contrast, a downward-pointing target was chosen less accurately on the lower shelf (2376 ms, 96.0%) than an upward-pointing target on the same shelf (2453 ms, 99.7%), t(23) = 3.21, p < 0.01, Cohen's d = 0.18, with comparable RTs, t(23) = 0.87, p = 0.40, indicative of the absence of the DPTS effect.

Similar to Experiment 1, we once again log-transformed the accuracy data in Experiment 2, and performed the Target Orientation × Target Location ANOVAs. None of the main or interaction effects were significant on the transformed accuracy data of the identification responses, all Fs < 1.90, ps > 0.18. As for the transformed accuracy data of choosing responses, the results revealed a significant main effect of Target Orientation, F(1,23) = 5.10, p = 0.03, η 2 p = 0.18, a marginally significant main effect of Target Location, F(1,23) = 3.70, p = 0.07, η 2 p = 0.14, and a marginally significant interaction term, F(1,23) = 4.03, p = 0.06, η 2 p = 0.15. Therefore, the patterns of results we obtained with transformed accuracy data were consistent with those with raw data.

#### Ratings of Stimuli in the Downward- and Upward-Pointing Orientations

The mean ratings for each stimulus in the downwardand upward-pointing orientations were summarized (see **Table 1**). The 2 (Triangle Orientation: downward- or upwardpointing) × 4 (Stimulus Type, red wine, white wine, whiskey, or baijiu) ANOVAs on these scores revealed a significant main effect of Triangle Orientation on familiarity scores, F(1,23) = 4.26, p = 0.05, η 2 p = 0.16, but not on any of the other three scores, all Fs < 2.06, ps > 0.16. These results therefore suggest that

TABLE 1 | Ratings of valence, arousal levels, familiarity, and liking (on 7-point scales) for downward- and upward-pointing stimuli (with SDs in parentheses) in Experiment 2.

the same bottles were rated as more familiar when the triangle in its label was oriented in the downward-pointing direction than when they were shown in the upward-pointing orientation instead, with comparable ratings of pleasantness, arousal, and liking scores. The results also revealed significant main effects of Stimulus Type on valence, F(1,23) = 5.16, p < 0.01, η 2 p = 0.18, familiarity, F(1,23) = 4.93, p < 0.01, η 2 p = 0.18, and liking scores, F(1,23) = 10.80, p < 0.001, η 2 p = 0.32. None of other main effects or interaction terms was significant on any of the scores, all Fs < 1.67, ps > 0.18. By contrast, the simple triangle, when presented by itself, received lower valence scores when oriented in the downward-pointing direction than when it was presented in the upward-pointing orientation instead, F(1,23) = 4.18, p = 0.05, η 2 p = 0.15, with comparable arousal, familiarity, and liking scores, all Fs < 2.83, ps > 0.10. Taken together, these results therefore suggest that the downward-pointing triangle was considered to be less pleasant than the same stimulus oriented in the upward direction, whereas such ratings did not influence how pleasant people considered the bottles having these triangles on the labels.

Last, but by no means the least, the participants reported that they occasionally (83%) or never (17%) consumed alcoholic drinks in daily life, and they occasionally (46%) or never (54%) purchased alcoholic drinks on their own.

### Discussion

The results of Experiment 2 revealed a significant DPTS effect when the participants chose the target bottle on the top shelf, whereas no such effect was observed with the target bottle presented on the second shelf or in their responses of identifying the shelf on which the target was located. Taken together with the results of Experiment 1, we replicated the DPTS effect with the visual search for bottles of wine in a virtual shopping situation, thus suggesting that incorporating a downward-pointing triangle on a wine label might influence people's attention in situations that are more complex and realistic than laboratory-based experiments.

On the other hand, even though the participants considered the downward-pointing triangle to be less pleasant than the upward-pointing one (see also Shen et al., 2015), we found no significant difference in the pleasantness rating scores of the same bottles of wine with a triangle pointing downward vs. upward. It is worth noting that these results are inconsistent with Westerman et al.'s (2013) findings that bottles of water or vodka with several downward-pointing triangles on their labels were rated as being less liked, less appealing, and less likely to be purchased than those with upward-pointing ones. It should be noted that their study and ours used different types of drinks, different label designs, and different groups of participants, all of which might contribute to the discrepancy between the rating results (see also Spence, 2012). Most importantly, several small triangles were presented on the left or right of the label in their study, which makes the triangles a more salient feature of the packaging, whereas we only presented one distinctive triangle on the center of the wine labels. Taken together, these results also suggest that people's ratings of the bottles with triangles on the labels might be modulated by many other factors, such as the contextual information.

#### GENERAL DISCUSSION

In the present study, we ran two VR-based experiments to examine the influence of having triangles (downward or upward oriented) on wine labels on people's visual search for wines. The participants walked along the wine aisle in a virtual supermarket and searched for the wine bottle on the shelf that had a different triangle on its label from the other bottles. Generally speaking, the results of both experiments revealed that, if anything, choosing a bottle with a downward-pointing triangle on its label was faster than when it had an upward-pointing triangle on the label instead. It should be noted that these results are consistent with Zhao et al.'s (2016) findings with images of store shelves. Once again, we replicate the DPTS effect with naturalistic stimuli where the triangle was only a local feature in a simulated shopping situation.

These results cannot easily be interpreted by the "Shape of Threat" account proposed by Larson et al. (2007, see also Larson et al., 2012; Watson et al., 2012), for at least two reasons. For one, the bottles of wine with downward-pointing triangles on their labels were not rated as being any more unpleasant than those with upward-pointing triangles. Due to the lack of the

associations between the bottles of wines with a downwardpointing triangle in their labels and negative subjective emotional ratings, the facilitated search for these bottles of wines may not be simply attributed to the affective features of the stimuli. For another, these wine bottles that the participants were asked to choose in a virtual store has no relation to threat of any kind whatsoever. Alternatively, the DPTS effect observed with non-threatening images (Shen et al., 2015; Zhao et al., 2016) and objects, as in the present study, are more in line with the possibility that the downward-pointing triangles more readily capture people's visual attention because of particular perceptual features, such as the lack of stability and people's expectations of the consequences of that perceived instability. Previous studies have shown that unstable shapes might be ascribed feelings of fear (Pavlova et al., 2005), while unstable-looking logos might be used to infer the presence of unsafe conditions (Rahinel and Nelson, 2016).

The results of the present study also revealed a position effect in visual search for the wines. On the one hand, the participants were faster to identify the target when it was presented on the top shelf than when it was presented on the second shelf. On the other hand, the position of the target shelf also modulated the DPTS effect. These results are in line with other position effects whereby, for instance, products presented at a higher location in the rack tend to attract more attention (Chandon et al., 2009; though see also Sunaga et al., 2016). What is more, it should be noted that consumers might use in-store displays as a source of information when trying to assess the quality and likely price of the products (Valenzuela and Raghubir, 2009). Here it is worth noting that products on higher shelves are generally assumed to be of better quality and have higher price than those placed on lower shelves (Valenzuela et al., 2013; Valenzuela and Raghubir, 2015). Therefore, in the present study, wines presented on the top shelf might attract more attention and are considered to be better, which might be important factors for the DPTS effect to emerge. It is worth noting that the vertical location of an object might also be associated with stimulus valence (for a recent review, see Cian, 2016). For example, negative words are recognized more rapidly when placed at the bottom of a computer screen, whereas positive words are recognized more rapidly when they placed at the top of the screen, suggesting an association between "being higher" and "being better" (Meier and Robinson, 2004). Taken together, these results suggest that having the downwardpointing triangle on the label of products which are assumed to be good might guide people's attention more efficiently, whereas it might not work if the products are not considered in this way.

There are also some straightforward limitations in the present study that should be acknowledged. First, as for a lab experiment conducted on a university campus, the participants were Chinese college students (see Henrich et al., 2010, for the discussion of biased samples) who at most, only occasionally drink or purchase alcoholic drinks. Previous research has revealed that older frequent wine consumers' evaluation of wine was more strongly influenced by brand and packaging (Mueller and Szolnoki, 2010), while the present study conducted with young inexperienced consumers might even underestimate the influence of wine labels on consumers' visual attention. What is more, it will be also interesting in future research to examine the possible crosscultural differences in the participants' ratings of the stimuli. On the other hand, it is also worth bearing in mind that those customers who purchase alcoholic drinks in stores are not necessarily the ones who drink it. For example, back in the 1950's, Cheskin (1957, see also Cheskin, 1981) reported that rounding the corners of the labels on the front of one brand of gin bottle made these more appealing to these female customers who purchase gins for their husbands to drink.

Second, in addition to the triangles on the wine labels shown in the present study, each bottle also has an upward-pointing V form in its shape because the neck of the bottle is narrower than the body, which might introduce an additional confounding factor of "global/local congruency." That is, when a bottle has a downward-pointing triangle on its label, the orientations of the triangle on the wine label and the bottle are inconsistent with each other; whereas the orientation of the upward-pointing triangle on the wine label is consistent with the bottle. Therefore, future research is called for in which the shape of the product is better controlled for. What is more, it will be also interesting to use heterogeneous distractors in other shapes on the wine labels such as circles and squares, which might be a more natural situation in daily life.

# CONCLUSION

Once again, our results demonstrate how the appearance of the bottles, in particular, the design of the wine labels, might guide consumers' attention when searching for the product presented on the store shelves (Thomas and Pickering, 2003; Elliot and Barth, 2012; Zhao et al., 2016). Changing the labels of the product might be a more efficient and effective way to attract consumers' attention than changing the appearance of the product, while increased attention might lead to greater likelihood of it being chosen (Orquin and Loose, 2013).

# ETHICS STATEMENT

This study was carried out in accordance with the ethical standards for conducting research established by the American Psychological Association with written informed consent from all subjects. The protocol was approved by the ethics committee of the Psychology Department of Tsinghua University.

# AUTHOR CONTRIBUTIONS

Each of the listing co-authors made the following contributions to the paper: HZ, FH, CS, and XW co-developed the idea for the study. HZ, FH, and XW collaboratively designed the study. HZ collected the data and conducted the data analysis. HZ, FH, CS, and XW conducted the interpretation of the data, and drafted the manuscript. All of the authors have read and approved the final version of the manuscript.

# FUNDING

fpsyg-08-02173 December 12, 2017 Time: 16:57 # 10

This research was supported by the National Natural Science Foundation of China (Grant No. 71472106) awarded to XW and Tsinghua University Initiative Scientific Research Program.

### REFERENCES

Cheskin, L. (1957). How to Predict What People will Buy. New York, NY: Liveright.

### ACKNOWLEDGMENT

The authors would also like to thank Jichengsi Guo, Hanxiang Zhou, and Kaung Myat for their assistance in the preparation of the experimental stimuli and procedure.

**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.

The reviewer AC and handling Editor declared their shared affiliation.

Copyright © 2017 Zhao, Huang, Spence and Wan. 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.

# Galvanic Tongue Stimulation Inhibits Five Basic Tastes Induced by Aqueous Electrolyte Solutions

Kazuma Aoyama1 \*, Kenta Sakurai2 \*, Satoru Sakurai3 , Makoto Mizukami4 , Taro Maeda2,5 and Hideyuki Ando2,5

1 School of Interdisciplinary Mathematical Sciences, Meiji University, Tokyo, Japan, 2 Graduate School of Information Science and Technology, Osaka University, Suita, Japan, 3 Lighting Business Division Lighting Equipment Business Unit Development Group, Panasonic Corporation Eco Solutions Company, Kadoma, Japan, 4 Microsoft Japan Co., Ltd., Tokyo, Japan, 5 Center for Information and Neural Networks, National Institute of Information and Communications Technology, Suita, Japan

#### Edited by:

Anton Nijholt, University of Twente, Netherlands

#### Reviewed by:

Kasun Karunanayaka, Imagineering Institute, Malaysia Takafumi Koike, Hosei University, Japan Nimesha Ranasinghe, National University of Singapore, Singapore

#### \*Correspondence:

Kazuma Aoyama<EMAIL_ADDRESS>Kenta Sakurai<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Human-Media Interaction, a section of the journal Frontiers in Psychology

Received: 30 August 2017 Accepted: 20 November 2017 Published: 05 December 2017

#### Citation:

Aoyama K, Sakurai K, Sakurai S, Mizukami M, Maeda T and Ando H (2017) Galvanic Tongue Stimulation Inhibits Five Basic Tastes Induced by Aqueous Electrolyte Solutions. Front. Psychol. 8:2112. doi: 10.3389/fpsyg.2017.02112 Galvanic tongue stimulation (GTS) modulates taste sensation. However, the effect of GTS is contingent on the electrode polarity in the proximity of the tongue. If an anodal electrode is attached in the proximity of the tongue, an electrical or metallic taste is elicited. On the other hand, if only cathodal electrode is attached in the proximity of the tongue, the salty taste, which is induced by electrolyte materials, is inhibited. The mechanism of this taste inhibition is not adequately understood. In this study, we aim to demonstrate that the inhibition is cause by ions, which elicit taste and which migrate from the taste sensors on the tongue by GTS. We verified the inhibitory effect of GTS on all five basic tastes induced by electrolyte materials. This technology is effective for virtual reality systems and interfaces to support dietary restrictions. Our findings demonstrate that cathodal-GTS inhibits all the five basic tastes. The results also support our hypothesis that the effects of cathodal-GTS are caused by migrating tasting ions in the mouth.

 This fact was first discovered by Sulzer in the 18th century. The technology has been used for gustatory testing in medical research and as a tool in neural science (Krarup, 1958; Von Békésy, 1964; Cardello, 1981). As GTS can induce taste without consumption of solids or liquids, this technology would be effective in providing a virtual consumption experience and in supporting dietary restrictions. Therefore, GTS is likely to be employed for virtual reality and health engineering purposes (Vazquez-Buenosaires et al., 2003; Aruga and Koike, 2015; Ranasinghe and Do, 2017). For such engineering applications, GTS should be able to preferably regulate all the five taste sensations, i.e., sweetness, bitterness, saltiness, sourness, and umami. However, the electrical taste induced by GTS is extraordinarily complex and it has been generally known as a method to induce electrical taste (Lawless et al., 2005). Conventional studies about GTS reported that an electrical taste is induced when the anode is in the proximity of the tongue (anodal-GTS) (Platttig and Innitzer, 1976; Ranasinghe et al., 2013). On the contrary, Hettinger and Frank (2009) demonstrated that GTS inhibits the taste of salt solutions when the cathodal electrode alone is placed in the subject's mouth

(cathodal-GTS). Although their studies demonstrate the inhibitory effects of cathodal-GTS on salty and bitter-salty tastes, the group did not investigate whether other basic tastes were affected. Moreover, the inhibitory mechanism was not adequately investigated.

Currently, two tentative hypothesis of the cathodal-GTS inhibitory mechanism exist: the ionic migration hypothesis and the nervous stimulation hypothesis. The ionic migration hypothesis postulates that the electrical field formed by the GTS current migrates and removes the tasting ions from the tongue (Hettinger and Frank, 2009) (**Figure 1**). In contrast, the nervous stimulation hypothesis, which is the simplest considerable alternate hypothesis, states that the electrical current disrupts nerve activation or habituates nerves. In anodal-GTS, Volta and Bujas proposed that stimulation current directly affects (may depolarize) taste cells or taste nerves (Bujas, 1971; Nakamura and Miyashita, 2016). Therefore, it is rational to consider that in cathodal-GTS, the cathodal current directly deactivates nerves or brings a negative effect. The objective of the present study is to determine the inhibitory mechanism of cathodal-GTS, and to investigate whether it influences all five basic tastes.

The gustatory sensors, referred to as the taste buds, detect chemicals in the mouth, which constitute the sense of taste. Each taste bud contains taste cells, which have receptors at the surface of the cell (Chandrashekar et al., 2006) that detect materials in aqueous solutions (Kandel et al., 2014). From this perspective, materials that generate tastes can be divided into two categories: electrolytes and non-electrolytes. If the nervous stimulation hypothesis is valid, the cathodal-GTS should inhibit the taste induced by both electrolytes and nonelectrolytes. However, if the ionic migration hypothesis is valid, then the cathodal-GTS should inhibit only the taste induced by electrolytes. As it has not been demonstrated that cathodal-GTS inhibits tastes apart from saltiness, we support the ionic migration hypothesis as the mechanism of taste inhibition by cathodal-GTS.

To demonstrate the validity of the ionic migration hypothesis, we conducted an experiment in which subjects were exposed to four types of aqueous solutions, i.e., sucrose, glycine, caffeine, and MgCl2. Sucrose and glycine exhibit sweet tastes, and caffeine and MgCl2 exhibit bitter tastes. Sucrose and caffeine are non-electrolytes, while glycine and MgCl2 are electrolytes (Stone and Oliver, 1969). We used only those materials that exhibit sweetness and bitterness because non-electrolytes that elicit umami, acidity, or salty tastes are unknown. For this experiment, subjects regulated concentrations of sucrose and MgCl2 solutions so that the strengths of the two become equivalent to the strength of glycine and caffeine solutions, respectively. The effect of cathodal-GTS on the subject's capability to taste electrolyte and non-electrolyte solutions was investigated using these fixed concentrations. To analyze their capability to taste sweetness, subjects tested the following pairs: glycine with GTS vs. without GTS, sucrose with GTS vs. without GTS, glycine without GTS vs. sucrose without GTS, and glycine with GTS vs. sucrose with GTS. To analyze their capability to taste bitterness, subjects tested the following pairs: MgCl2 with GTS vs. without GTS, caffeine with GTS vs. without GTS, MgCl2 without GTS vs. caffeine without GTS, and MgCl2 with GTS vs. caffeine with GTS. Subjects verbally answered whether one of the samples had a stronger taste than the other or not.

Subsequently, we investigated whether cathodal-GTS could inhibit all five basic tastes induced by aqueous electrolyte water solutions, and the relation between the strength of cathodal-GTS and the inhibitory effect on taste. Subjects were provided with five types of aqueous electrolyte solutions, namely, NaCl, MgCl2, glycine, glutamic sodium, and citric acid, with salty, bitter, sweet, umami, and sour tastes, respectively. Each type of solution was prepared in five concentrations (**Table 1**). The solution with the highest concentration in each type was termed the "adjusting sample," while the others were termed "comparable samples." In each trial, a subject first tasted the comparable sample. Then, the subject attempted to adjust the taste intensity of the adjusting sample to match it to that of the comparable sample by altering the current intensity of the cathodal-GTS.

Therefore, the contributions of this work to the field of electrical taste, taste physiology, or taste psychology are the following:

# MATERIALS AND METHODS

All the experiments complied with the safety standards approved by the local ethics research committee at the Graduate School of Information Science and Technology, Osaka University, Japan. All the participants had the experiments explained to them and signed a letter of consent. The study protocol was performed in accordance with the ethical standards laid down in the Declaration of Helsinki.

In terms of safety thresholds for electrical stimulation, we followed the safety guidelines for transcranial direct current stimulation (tDCS). Since there are no standard limitations for GTS, various stimulation strengths and durations were used in previous studies, e.g., up to approximately 55 mA but some studies described the voltage instead of the current strength (Aruga and Koike, 2015; Khan et al., 2016). tDCS is a technique for modulating brain and neuronal excitability by stimulating the head electrically. The paper published by Bikson et al. (2016) indicated that the use of conventional tDCS protocols in human trials for up to 40 min and at 4 mA has not produced any reports of serious adverse effects or irreversible injury in over 1000 subjects. GTS is similar to tDCS in that it stimulates the head electrically. Therefore, we believe that the stimulation limitations for tDCS should be employed for GTS. In this work, we employed safer limitations than that of tDCS, i.e., the stimulation current is only up to 2.5 mA and the longest stimulation duration is 30 s to ensure the safety of subjects. In fact, all subjects used up to 1 mA of current except for one subject who used a maximum current of approximately 2.3 mA.

In all experiments, we used an in-house constant current stimulator, which consists of an operation amplifier (LMC6482), MOSFET (2SK3113), and transistor (2SA1413). This circuit is driven by a microcontroller (18F2620) that receives commands from a PC.

# Effect of Cathodal-GTS on Sweet and Bitter Tasting Electrolyte and Non-electrolytes

Eight male participants enrolled in this experiment. An anodal electrode (NIPLODE, Fukudadenshi, Inc., Tokyo, Japan) was attached to the back of the neck, and a conductive wire that passed through a drinking straw was used for the cathode (**Figure 1**). The reason why we attached the anodal electrodes to the back of the neck is because this position induces white flash visual sensations and ticking sensations on the skin vanishingly compared with electrode positions in previous works (Hettinger and Frank, 2009; Aruga and Koike, 2015). During the preliminary phase of this experiment, subjects adjusted the concentrations of sucrose and MgCl2 aqueous solutions so that they exhibit taste strengths identical to those of aqueous solutions of 5.0% glycine and 0.3% caffeine, respectively. Using these fixed sucrose and MgCl2 samples and the 5.0% glycine and 0.3% caffeine samples, subjects were presented four types of conditional sample-pairs for each taste quality. The following pairs were presented for the

TABLE 1 | Consistency of adjusting material and comparable materials in the second experiment.

TABLE 2 | Experimental conditions.

sensation of sweetness: glycine with GTS vs. without GTS, sucrose with GTS vs. without GTS, glycine without GTS vs. sucrose without GTS, and glycine with GTS vs. sucrose with GTS. The following were presented for the sensation of bitterness: MgCl2 with GTS vs. without GTS, caffeine with GTS vs. without GTS, MgCl2 without GTS vs. caffeine without GTS, and MgCl2 with GTS vs. caffeine with GTS. Cathodal-GTS was applied using a 1.0-mA and 2000-ms square current. In each trial, the subject tasted each of the two comparable solutions once. Each condition was repeated four times, and the 16 trials were conducted in a random sequence for each taste quality.

# Relation between the Strength of Cathodal-GTS and Inhibitory Influences on the Five Basic Tastes

Six adult male participants enrolled in this experiment. An anodal electrode (NIPLODE, Fukudadenshi, Inc., Tokyo, Japan) was attached to the back of the neck, and a conductive wire that passed through a drinking straw was used as the cathode. Solutions of glycine, MgCl2, NaCl, glutamic sodium, and citric acid were used as the taste samples.

Each solution was prepared in five concentrations (**Table 1**); the solution with the highest concentration was termed "adjusting sample," while the others were termed "comparable samples." In each trial, a subject first tasted the comparable sample. Then, the subject was asked to adjust the strength of the

taste of the "adjusting sample" to that of the "comparable sample" by using a sliding volume controller connected to the stimulator. This sliding volume was connected to a microcontroller (NXP mbed LPC 1768) which sends commands to a PC, which then sends commands to the constant current stimulator. The current strength ranged from 0 to 2.5 mA and longest current duration was 30 s. However, all subjects finished adjusting the slide volume within 30 s. Each combination of the adjusting and comparable samples for each taste quality was tested six times. Thus, each subject completed 120 trials. Owing to safety limitations, the trials for only one tasting sample were conducted in 1 day. The sequence of the trials was randomized. The sampled current intensity data were normalized for each subject by dividing the data by the maximum current intensity recorded for the subject.

The differences in conditions between the first and second experiments are shown in **Table 2**.

#### RESULTS

# Examining the Influence of Cathodal-GTS on Sweet and Bitter Tasting Electrolyte and Non-electrolytes

**Figures 2** and **3** illustrate the results for the sensations of sweet and bitter tastes, respectively.

**Figures 2A** and **3A** compare the average selection percentage between the electrolytes and non-electrolytes in eliciting a sensation of sweetness and bitterness, respectively. Statistical analyses, performed with Kruskal–Wallis analysis of variance (ANOVA) and multiple comparisons (Scheffe's method) test, on the response percentages demonstrated that the percentage of "similar level" responses were significantly higher than the others (**Figure 2A**: F2, 21 = 8.55, p < 0.05; **Figure 3A**: F2, 21 = 11.81, p < 0.05). This indicates that the strength of taste of the electrolyte and non-electrolyte samples were sensed as being similar.

**Figures 2B** and **3B** demonstrate the effect of cathodal-GTS on the sensations of sweetness and bitterness, respectively, which were elicited by the electrolytes. Statistical analyses performed using the Kruskal–Wallis ANOVA and Scheffe's method discovered that Cathodal-GTS weakened both the taste sensations (**Figure 2B**: F2, 21 = 16.28, p < 0.05: **Figure 3B**: F2, 21 = 18.01, p < 0.05). However, cathodal-GTS did not demonstrate an effect on the sweet and bitter tastes that were elicited by the non-electrolytes, i.e., sucrose and caffeine, as the percentages of "similar level" responses were significantly higher in comparison with the other conditions (**Figure 2C**: F2, 21 = 19.92, p < 0.05; **Figure 3C**: F2, 21 = 9.51, p < 0.05).

Finally, the effect of cathodal-GTS on the electrolyte and nonelectrolyte, eliciting sweetness or bitterness, are illustrated in **Figures 2D** and **3D**, respectively. Cathodal-GTS affected only the taste sensation of the electrolytes, i.e., glycine and MgCl2 (**Figure 2D**: F2, 21 = 17.28, p < 0.05; **Figure 3D**: F2, 21 = 16.15, p < 0.05).

## Investigating the Relation between the Strength of Cathodal-GTS and Inhibitory Effects on the Five Basic Tastes

**Figure 4** illustrates the normalized and averaged current strength that was required to inhibit the taste of the adjusting sample so that the taste strength was similar to the strength of comparable sample. The solutions used were glycine, MgCl2, citric acid,

FIGURE 3 | Influence of cathodal-GTS on the bitterness of electrolyte and non-electrolyte aqueous solutions. These figures indicate the percentage of selection in each condition: (A) Caffeine vs. MgCl2 without GTS, (B) MgCl2 without GTS vs. with GTS, (C) Caffeine without GTS vs. with GTS, (D) Caffeine with GTS vs. MgCl2 with GTS. Data reported as mean ± standard error of mean. Asterisks (∗ ) in these figures reveal the significant differences (p < 0.05) detected by statistical analysis using Kruskal–Wallis ANOVA and multiple comparisons test (Scheffe's method).

NaCl, and glutamic sodium, which elicit sweet, bitter, sour, salty, and umami tastes, respectively. The concentration of the comparable sample was negatively correlated with the strength of the current for all the five types of electrolyte solutions. Statistical analyses performed using the Kruskal–Wallis ANOVA and Scheffe's method for each graph demonstrated significant variations between the conditions (**Figure 4A**: F3, 140 = 72.54, p < 0.05; **Figure 4B**: F3, 140 = 72.82, p < 0.05; **Figure 4B**: F3, 140 = 81.47, p < 0.05; **Figure 4B**: F3, 140 = 98.42, p < 0.05; **Figure 4B**: F3, 140 = 75.52, p < 0.05).

## DISCUSSION

The results of the first experiment demonstrate that, while cathodal-GTS does not effectively inhibit tastes induced by

non-electrolyte solutions, it inhibits those induced by electrolyte solutions. **Figures 2A** and **3A** indicate that the electrolytes and non-electrolytes elicited tastes with similar strengths. However, when cathodal-GTS was applied, it weakened the sensation of the taste elicited by the electrolytes: glycine and MgCl2 (**Figures 2B**, **3B**); however, it did not adequately influence the non-electrolytes: sucrose and caffeine (**Figures 2C**, **3C**). The fact is further emphasized by the results illustrated in **Figures 2D** and **3D**.

Cathodal-GTS inhibited the sensation of sweet and bitter tastes elicited by the electrolytes, but did not effectively for nonelectrolytes. These results support the ionic migration hypothesis as the mechanism of the taste inhibition. The major dissimilarity between electrolyte and non-electrolyte aqueous solutions is the production of ions. Electrolytes become ions in solution, while non-electrolytes do not. Therefore, ionic migration occurs when a current stimulation is applied to the electrolyte solution. During ionic migration, the electrical field formed by the GTS current impels cations and anions toward the cathode and anode, respectively. The ionic migration hypothesis matches with our experimental results that only the tastes induced by the electrolyte solutions were inhibited by the electrical field.

**Figure 4** indicates that the five basic tastes induced by electrolytes were inhibited by cathodal-GTS, and that this effect is strongly correlated with the strength of the current. The correlation coefficient for each condition was 0.9 or higher. Therefore, the strength of taste sensation is highly likely to be regulated by the strength of the current.

All subjects reported that the taste strength they experienced immediately after the stimulation offset was stronger than that they experienced prior to stimulation for all the electrolyte solutions. Hettinger and Frank (2009) reported a similar phenomenon with salty and bitter-salty solutions. However, in the first experiment in our study, the subjects did not experience taste enhancement with the non-electrolyte solutions. This indicates that the taste enhancement is caused by the preceding taste inhibitory effect. We have two descriptions of the mechanism of taste enhancement. The first is the nerve adaptation hypothesis, which postulates that taste receptors and nerves adapt to the low taste-intensity environment while GTS was applied, and then, is more strongly activated by a normal taste-intensity when GTS was stopped, resulting in the taste enhancement. Another description is that the taste ions that were attracted to each pole became diffuse when GTS ceased. The taste receptors on the tongue would be stimulated at a high frequency, resulting in a temporarily stronger taste sensation. The current study, however, is not sufficient to reveal which description is appropriate.

During the first experiment, one subject for MgCl2 and two subjects for glycine reported that cathodal-GTS did not inhibit taste. However, they reported the inhibition with a similar configuration on another day. On the other hand, those who continuously reported the effect reported that the strengths of the effects differ day to day. We recognize that these occurrences are results of alterations in the physical conditions of the subjects and the precise positions of the electrodes and the subjects' tongues. Especially, since glycine is zwitter ion, the state of the inner mouth (e.g., pH and so on) may hugely affect the state of ions of glycine (Tse et al., 1978).

Moreover, some subjects verbally reported that during trials for citric acid, they felt electrifying sensations on their tongues and, at the end of the sessions, they had difficulty distinguishing between the effects of GTS and the masking effect caused by the electrifying sensation. Some also reported that taste was inhibited by the ticking sensation induced by the combination of citric acid and GTS.

This study validated the hypothesis that ionic migration is the mechanism of cathodal-GTS, which inhibits all five basic tastes. Our observations contribute to the physiological understanding of how cathodal-GTS functions, and could be applied as tools for dietary restrictions by altering meal experience.

In our preparatory experiment, we confirmed that cathodal-GTS does not affect the taste elicited by Na-saccharin. The fact is also reported in the previous works conducted by Hettinger and Frank (2009). They reported the taste inhibition for saltiness but they did not consider the state of electrolytic dissociation in the mouth. For use of cathodal-GTS in VR or diet restriction, it is preferable to control all five basic taste in the meal. To achieve this, the migration of all taste materials should be controlled. It would be our future work to model the ionic migration in the mouth, which considers degree of electrolytic dissociation, molar weight, and ionic polar character.

# CONCLUSION

In this work, we demonstrated that the ionic migration hypothesis is valid explanation of mechanisms for the taste inhibitory by cathodal-GTS. We also revealed that cathodal-GTS is able to inhibit all five basic tastes which is elicited by electrolyte water solutions.

# AUTHOR CONTRIBUTIONS

KA and SS proposed the hypothesis and conducted the experiments. KA, SS, and HA designed the experiments. KS, MM, and TM assisted with the experimental setup. SS and KA collected and analyzed the data. KA, MM, and HA wrote the manuscript. All the authors discussed the results and commented on the manuscript. The works by MM and SS have done at Osaka University when they were students and are not to represent interests of Microsoft and Panasonic Corporation Eco Solutions Company.

# ACKNOWLEDGMENT

This work was supported by JSPS KAKENHI Grant-in-Aid for Young Scientists (A) Grant Number 17H04690.

# REFERENCES

fpsyg-08-02112 December 2, 2017 Time: 15:56 # 7

**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 © 2017 Aoyama, Sakurai, Sakurai, Mizukami, Maeda and Ando. 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.

# Development and Testing of a Small-Size Olfactometer for the Perception of Food and Beverages in Humans

#### Paola Risso1 \*, Mario Covarrubias Rodriguez 2 , Monica Bordegoni 2 and Alberto Gallace1

1 Department of Psychology, Milan Center for Neuroscience, University of Milano-Bicocca, Milan, Italy, 2 Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy

Studies of olfactory perception and about the way humans interact with, and perceive food and beverages require appropriate olfactory devices. Moreover, small size, and portable interfaces are needed within the context of Human Computer Interaction (HCI), to enrich and complete the design of different mediated experiences. In this paper, the authors tested a new portable olfactory device for the orthonasal administration of smells. The main aim was to verify if the experience generated by the odors delivered through such device can affect people's taste perception. Once established that people could perceive odors using the olfactory device, a group of participants was asked to taste two different types of food (Experiment 1) and three types of beverages (Experiment 2) and to evaluate them on a number of perceptual-dimensions (such as pleasantness, freshness, sweetness, saltiness, and bitterness). The participants could taste the food and the beverage without the presence of additional olfactory stimuli, or under conditions where olfactory stimuli (the smell of chocolate or citrus) were also presented using the device. The results showed that the participants' evaluation of food and beverages was significantly modulated by the concurrently presented odors. The experimental results suggest that: (1) the device is effective in controlling the delivery of odors to human participants without the complexity of management that often affect larger odors delivery systems; (2) odors administered by means of such device can have an effects on food and beverage perception, without the need to change their chemical properties.

Keywords: olfaction, taste, human machine interfaces, multisensory interaction, cognitive neuroscience, gustatory perception

# INTRODUCTION

In Human-Computer Interaction (HCI), olfaction is rarely included as interaction modality. This is, at least in part, because: (1) most of the available devices for odor presentation are extremely costly, cumbersome and not easily manageable by non-expert technicians; (2) scientific knowledge of olfactory perception is less developed as compared to other sensory modalities. The implementation of devices able to simulate a real flavor experience by means of trigeminal and tactile taste stimulation has proven to be a difficult task. Technical difficulties associated with the digitization of flavors and odors have likely contributed to the reduced commercial success

#### Edited by:

Carlos Velasco, BI Norwegian Business School, Norway

#### Reviewed by:

Maria G. Veldhuizen, John B. Pierce Laboratory, United States Marianna Obrist, University of Sussex, United Kingdom Massimiliano Zampini, Università di Trento, Italy

> \*Correspondence: Paola Risso

<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Human-Media Interaction, a section of the journal Frontiers in Digital Humanities

> Received: 31 May 2017 Accepted: 05 April 2018 Published: 24 April 2018

#### Citation:

Risso P, Covarrubias Rodriguez M, Bordegoni M and Gallace A (2018) Development and Testing of a Small-Size Olfactometer for the Perception of Food and Beverages in Humans. Front. Digit. Humanit. 5:7. doi: 10.3389/fdigh.2018.00007

of the devices that have been developed so far for this purpose (see Spence et al., 2017, for a detailed review). As consequence, it is still hard nowadays to effectively use smell by means of an olfactometer device, especially under conditions of multisensory stimulus presentation (Sanders and McCormick, 1993; see Barfield and Danas, 1995; Nakaizumi et al., 2006; Nakamoto, 2012). In this work, we propose and test a new and innovative olfactory display able to present multiple odors to human participants.

A brief review follows on the state of the art of olfactory devices. In particular, the focus of the review will be on the description of the most recent miniaturized and portable olfactory devices.

# State of the Art of Portable Olfactory Devices

Generally, the term "olfactometer" is used to describe complex devices, mainly used in a laboratory setting in a standardized computer-controlled manner with determined air flow, odor concentration, odor duration, onset, and offset (Al Aïn and Frasnelli, 2017). Such devices are often custom-built prototypes, although a few commercial versions do exist. Usually, these devices are very expensive and exceed the financial budget available for the largest part of research laboratories. Moreover, because of their technical characteristics, the majority of these olfactometers are cumbersome, not practical to handle and often not easily transportable or wearable.

Recently, a series of olfactory devices designed for administering odors in less controlled and more ecological situations have been developed (see **Table 1**). For example, jewelry or parts of clothing controlled by smartphones and pc accessories can now be used for odor delivery purposes. However, all these different approaches to olfactory stimulation have to face the challenge of using invisible, extremely volatile, and persistent stimuli. Moreover, they require a sophisticated miniaturization system to adequately spread the smells in the environment.

In those cases where the olfactory devices have been miniaturized, their potential use has been rather limited. For example, Nakaizumi et al. (2006) developed a device that makes use of two air cannons to project rings of odors directly to the nose of the participants. The authors implemented four prototypes of the device and the last, presented at the SIGGRAPH'2005, is capable of launching four different odorants. However, the size of the two cannons was not specified in the original reports. Nevertheless, despite of its high level of technological implementation, such device is certainly not easily transportable, at least in its current form (also note that precise distances and positions from the cannons are needed for the device to deliver the smell correctly). By contrast, an example of a small wearable and transportable device is the Essence necklace, designed to control odor intensity, and frequency of release through a smartphone (Amores and Maes, 2017). The scent delivery is controlled by an encapsulated piezoelectric transducer, which vibrates by emitting ultrasounds. Such transducer is immersed in the odorant liquid contained in a 3D printed cover, hang on the participant's neck. The ultrasonic sounds transform the scented liquid into vapor-like particles, which immediately are distributed around the necklace. The 3D print cover can contain 7 ml of an essence, sufficient to provide 27–28 h of continuous odor volatilization. Despite of its small size, it is important to note that this prototype allows delivering only one essence at a time, limiting its field of use to a very few situations (and without considering the problem of perceptual and neural adaptation to the same odor by humans).

A portable device that allows the delivery up to six scents through the digital integration of odors is Aroma Shooter (Aromajoin Corporation, Kyoto). Such a device delivers essences up to a distance of 600 mm by using a gas ejection method that allows the control of the directional air flow. The system uses a series of scented cartridges, which can be automatically changed at intervals of 1 s and can be remotely controlled by computers and mobile devices. Also, a wearable version of the same device, with the approximate size of a small pendant (the Aroma Shooter Mini), has been developed to deliver only one essence at a time.

A small olfactory device designed, once again, in the form of a piece of jewelery is the Mist Shine, produced by Indiegogo (Indiegogo). Mist Shine is a perfume spray bottle, which can be worn by the user. Such a device allows the liquid odorant to be transformed into a micron mist using an ultrasonic unit and be delivered by simply pressing a bottom. A version of this apparatus can be connected to the mobile devices through Bluetooth technology.

The largest part of the above mentioned olfactory devices are conceived as a part of a new trend in clothing, smartphone, and pc accessories and targeted to a wide range of fashion consumers. In the same vein, the Scentsory Design R & Technology Ltd., (Scentsory Design) designed the 'Aroma Rainbow Sensitive Dress'. The idea of this conceptual dress was born from a multi-disciplinary research project, with the aim of exploring the emotional fashion through the release of odorous molecules. In practice, several colored tubes corresponding to different scents are embedded in the dress. The odors are delivered to the user and to the environment using nanotechnology-based release systems. The tubes are activated by touch screen monitors according to their different color labels.

An extreme application of the odor delivery devices is the Swallowable Parfum R by Lucy McRae (Swallowable Parfum). In this case, the olfactory device is a digestible scented capsule that after the ingestion allows the body skin to emanate a unique fragrance. The odor is excreted by the skin in the form of droplets, which emanate a fragrance determined by the enzymes that metabolize fat in the human body. In this case, no change of the delivered odors would seem to be possible after the ingestion of the capsule. However, this new technology is based on chemical rather than electromechanical mechanisms.

Some years ago, another interesting transportable/wearable olfactory device was developed by Yamada et al. (2006). The aim of the authors was at enabling a person to identify the placement of an odor source in a virtual environment by changing its strength. Their device includes: (1) an Odor Presenting Unit worn by the user; (2) a backpack containing the odor generator unit that is used to modulate the strength of the essences

#### TABLE 1 | Key features of the reviewed devices.

according to the position of the carrier, (3) a neckband connected with a tube to the odor generator unit that conveys the essence to the user's nose, (4) a little bag attached to the waist containing the system to detect the position of the carrier by means a tag reader, (5) a breath detecting sensor to ensure that odors are administered to the user during the breath inhalation phase. All the wearable components have been miniaturized to give the minimum clutter and annoyance to the wearer. In particular, the Odor Presenting Unit carries smells to the nose using a piezotype inkjet head device. The piezo element component applies a pressure pulse to the tubule filled with the odorant liquid that directly reaches the nose in the form of droplets. The response time of the inkjet head device is 300 µs. Moreover, the wearable device is monitored by an Odor-Controlling Unit composed by a microcomputer that controls the air pump and a notebook PC that calculates the strength of odor presentation according to the data sent by the user's positioning system. Besides its very high technological level and the miniaturizations of its components, this olfactory device allows only a limited series of odors to be presented and still produces some degree of clutter for the wearer.

As recently pointed out by a number of authors (Obrist et al., 2016; Spence et al., 2017), in order to obtain good results in chemosensory digitization, it is necessary to take into account both technical and psychological limitations of an olfactory display. Moreover, the effectiveness of these devices should depend on the similarity of the human responses to the stimuli elicited by the device, concerning those occurring under natural emissions of odors (e.g., see the Smell Synthesizer of the Museum of Food and Drink's MOFAD Lab; Berenstein, 2015). That would seem to suggest that novel olfactory devices will need to be tested also using perceptual and neuroscientific experiments and paradigms.

#### Olfactory Crossmodal Integration

In the last decades, psychological and neuroscientific research has shown that the different features of a product, such as its color, shape, odor, taste, tactile feel, sound and so on, are rarely processed in isolation by our neural system. Some interactions occur among them, and human's final perception is much more than a mere sum of these characteristics (see Spence, 2011, 2017). This consideration also applies to food evaluation. In this context, the perception of taste should be considered a multisensory experience, rather than a unisensory experience (e.g., Spence et al., 2013). In fact, psychological and neuroscientific research has shown that visual, auditory, olfactory and tactile aspects of food (see Spence and Piqueras-Fiszman, 2014, for a recent review) can all modulate our gustatory perception. For example, Michel et al. (2014) reported that the participants in their experiment provided higher tastiness ratings when asked to taste a salad dish visually arranged in an artistic way (similar to a Kandinsky's paint), than when the same dish was presented without any artistic arrangement. As far as beverages are concerned, Zampini and Spence (2005) reported that participants' perception of carbonation intensity of sparkling mineral water is affected by an alteration of the frequency of the auditory feedback emitted by the liquid just before consumption. In particular, amplification of the higher frequencies emitted by the beverage when served, results in the participants reporting a higher intensity of carbonation while tasting the water.

Interestingly, several studies have also demonstrated that food perception is not only affected by the different sensory qualities of the food itself, but also by those of the context where food is presented. For example, the color of a container can affect the taste of food and beverage presented in it (e.g., Zampini and Spence, 2005; Krishna and Morrin, 2008; Piqueras-Fiszman et al., 2012; Spence and Wan, 2015; Biggs et al., 2016). In particular, Risso et al. (2015) recently reported that people perceive mineral water as more carbonated when contained in a red or blue plastic cup, than when contained in a white cup. Similarly, Stewart and Goss (2013) showed that different combinations of colors and shapes in a plate could significantly modify the sweetness, flavor intensity, quality, and enjoyment perception of the dessert served in them (see also Bruno et al., 2013). Even the weight of the container would seem to affect the perception of the beverage presented in it, where heavier cups make the participant perceive the mineral water less pleasant than when served in lighter cups (Maggioni et al., 2015).

As far as the crossmodal interaction between odors and food is concerned, it was demonstrated that an odor could also elicit a taste response in a tasteless solution, besides the expected olfactory response (Burdach et al., 1984). In a series of pioneering experiments, it was observed that strawberry odor enhanced the sweetness of a sucrose whipped cream, while peanut butter odor did not enhance such perception. Moreover, strawberry odor did not enhance the saltiness of sodium chloride. Interestingly, it was also shown that the color red, differently from the strawberry odor, did not modulate the perception of sweetness (Frank and Biram, 1988; Frank et al., 1989). It was also demonstrated that "cut grass smell" defined as a "green odor," enhanced bitterness perception (Caporale et al., 2004). Similarly, it was shown that the sardine aroma enhanced salt intensity in tasteless solutions or in low-salt content solutions (Nasri et al., 2012). That is, under natural conditions of stimulus presentations, certain odors can affect the perception of food and beverages. An effective olfactometer device should then lead to similar interactive effects.

Olfaction is certainly one of the most important sensory system used by humans to evaluate gustatory stimuli. In fact, it has been shown that our taste perception decreases when olfaction is not available (e.g., Murphy and Cain, 1980). By these observations, if one's aim is at modulating people's experience of food also under ecologically valid conditions of stimulus presentation, olfactory stimuli need to be presented effectively and in a highly controlled way. In particular, smallsize transportable olfactory interfaces would allow us to present in a timely precise context specific odors, which might modulate people's food experiences and choices.

# The Multi-Fragrance Olfactory Display (MFOD)

In this paper, a novel Multi-Fragrance Olfactory Display (MFOD), which is light, small and able to release multiple fragrances, was used for the presentation of odor stimuli in two behavioral experiments. The MFOD is a multi-odor dispenser consisting of small cases that release up to eight fragrances in a precisely controlled manner.

The MFOD is based on the SFR (Solid Fragrance Release) method for the generation and the release of fragrances. The SFR consists of delivering scents through the modulation of an airflow striking a tablet of solid fragrance. This method differs from that adopted in those devices where liquid or vaporous fragrances are delivered (which in turn are more "invasive" and permeating into the environment). Also, the use of solid particles delivered through airflow allows a more precise control of the flow.

The same principle can be used for the implementation of a wearable configuration and of a desktop configuration (Covarrubias et al., 2016). In this specific research, a desktop version of the MFOD was used (see **Figure 1**). It consists of an actuated dispenser able to store up to eight fragrances and to control timing, intensity, and duration of the fragrance release. The MFOD (see **Figure 1**) includes a centrifugal fan (1), which provides and controls the airflow, a servo-motor (2), a cylindrical repository (3), and eight small tubes including compact powder fragrances (4). The servo-assisted cylindrical repository is controlled through an Arduino board (arduino.cc), which is connected to the E-Prime tool (E-Prime). E-Prime is a software environment used for design, implementation, data collection, and analysis of computer-based behavioral experiments. In this work, it was used for the selection and delivery of the fragrances. Finally, a pipe (5) releases the selected odor to the user's nostrils.

The MFOD performs three main functions.

3. Odor Delivery– The airflow generated by the fan passes through the selected tube in the fragrance repository, and the odorous airflow, generated by an erosion process, goes through the flexible plastic pipe (600 mm length and 10 mm internal diameter) and is delivered close to the user's nose (about 3 cm from the pipe).

The fragrance intensity can be adjusted by modifying the airflow generated by the centrifugal fan. The latency from generation to the perception of a selected odor is <0.5 s. This time interval was calculated on the basis of a series of pre-tests performed by setting two characteristics of the device, i.e., the fan speed and the servo motor speed.

By using a small anemometer, which is a device for measuring the air speed with a fan, some measurements were taken at several points of the prototype when varying the input voltage of the DC fan from 5 to 20 Volt, as shown in **Figures 2**, **3**.

A further test was carried out to measure the time that the servo-motor takes to rotate the cylinder at specific angles. In particular, a rotation of 60◦ is performed in 0.16∼0.13 s. The configuration with 12 Volts was adopted to produce a perception of synchrony between the delivery of the fragrance and the presentation of the stimuli.

The device used in this study extends the functionalities of previous devices and reduces their limitations (i.e., technical complexity, use complexity, and size). In particular, the device can be used to deliver up to eight fragrances. Note, however, that its current design allows up to twenty odors to be easily delivered. Moreover, the olfactometer was designed to be easily interconnected with the software for behavioral research EPrime 2.0. Therefore, the device can be integrated into complex psychological and neurocognitive studies where a high level of

delivery tube 600 mm long.

control on timing, randomization of conditions, reaction times of participants is required. Additionally, by means EPrime 2 the olfactometer can be interconnected to other scientific devices (i.e., eye tracker, skin conductance response recorders, etc.).

The device might be used in a large number of applied contexts. In fact, the prototype used in the present study has been designed to be adapted both in experimental contexts, and in less controlled and more ecological contexts. For example, it might be used to deliver odors in virtual reality environments, where it would help to enhance the sense of presence (Bordegoni and Carulli, 2016; Carulli et al., 2016). The device might also be adopted to improve the effect of exposure therapies in posttraumatic stress disorders patients (see a detailed review of Aiken and Berry, 2015 on this topic), to alleviate the effect of pain in a number of clinical conditions (Marchand and Arsenault, 2002) or to provide alerting cues to drivers (Ho and Spence, 2017). Given the large numbers of odors which can be presented with this new device, one additional application of our system is also to provide a valid alternative to the odor kits (manually administered), that are used at the moment for testing olfactory capability in different populations of participants (e.g., see the small bottles of the kit for sommelier's training 'Le Nez du vin R , Sniffin' Sticks, University Pennsylvania Smell Identification Test).

In this paper, the authors used the olfactory display in order to determine if the sensory experience generated by the device affects people's evaluation of some food and beverage characteristics (just as it occurs for odors naturally present in the environment). In particular, in the experiments presented here, the olfactory device was used to modulate people's perception of four different qualities of food (Experiment 1; pleasantness, sweetness, saltiness, and bitterness) and of beverages (Experiment 2; pleasantness, sweetness, saltiness, bitterness, and carbonation intensity).

The main aim of the present research was to investigate whether the device might be used to deliver odors under conditions of multisensory stimulus presentation and to generate perceptual multisensory interactions between the concurrently presented stimuli (food and odors). It is important to highlight that in the present experimental design, the crossmodal interaction among foods, beverages, and odors was tested by only using two odors (despite the possibility of administering up to eight odors). Adding more odor-food combinations could have affected negatively the participants' evaluations due to the multiple interactive effects likely occurring during the presentation of a large number of foods and odors in a reduced amount of time.

#### EXPERIMENT 1

The aim of the experiment is to test the effect on food perception of the orthonasal presentation of odors administered by means the new small-size olfactory device. In particular, Experiment 1 aims at verifying if the experience generated by the odors delivered through such device can affect people's taste perception of two different types of food on a number of hedonic and perceptual-dimensions (such as pleasantness, freshness, sweetness, saltiness and bitterness).

#### Materials and Methods Participants

Twenty-two participants with a mean age of 24.5 years (SD = 6.84, 12 female), took part in the experiment. All the participants gave written informed consent before their participation. The experiments described here were all performed in accordance with the ethical standards laid down in the 2008 Declaration of Helsinki and approved by the local ethical committee. The experiment lasted for approximately 20–30 min. People who claimed to be affected by any permanent or temporary olfactory or taste dysfunction, were excluded from taking part in the study.

#### Stimuli

Two different types of food were used: salty crackers (Carrefour) and lemon sugar candies (Perugina). The stimuli have been selected in order to have opposite taste characteristics (salt and sweet), without changing their organoleptic quality during the experiment (such as fresh food). Common white plastic dishes (produced by Bibo Italy S.p.A. for Carrefour) were used to serve the food. The two odors administered were chocolate and a mixture of citrus fruit (Oikos Fragrances R ). The odor selection was focused on finding two completely different and easily classifiable smells. A very important characteristic of the fragrances used is to be made up of scented powder. This important innovation adopted in our device does not require the dilution of fragrances, thus making the delivery of odors much easier under experimental procedures.

#### Procedures

Before starting the experiment, a short pre-test was performed in order to evaluate people's ability to perceive the odors by means of the experimental device.  The participants were instructed to grasp and eat the food presented on the desk at a signal of the experimenter, while at the same time they smelled an odor or clear air administered to both nostrils for about 15 s. The odor was administered by means of a small pipe connected to the olfactometer and held attached to the participants' nose, just between their nostrils (at about 3 cm). The method for releasing the odorant molecules, based on SFR-Solid Fragrance Release, ensured that the flow of odorant molecules effectively reached the participant's nostrils. This method, as compared to the volatilization of liquid compounds, results to be more effective in preventing the dispersion of part of the odor molecules in the surrounding environment. Given that the process that leads to olfactory perception of the airflows dynamics and allows peripheral processing of the signal, is extremely complex and delicate, the experimenter avoided inserting the pipe directly into the participant's nostrils. In fact, the insertion of the tube into the participants' nostrils could have prevented an effective perception of the odor presented. As a consequence of this presentation modality, some odorant molecules administered through the MFOD in our experiment may likely have reached people's mouth as well as the nostrils, and thus be also processed by retronasal route. However, it should be considered that this is the natural condition in which human perceive orthonasal olfactory stimulation in everyday situations.

The administration modality and timing of the stimuli in Experiment 1 were defined using some pre-tests. This procedure assured that all participants started to smell the odor before grasping the food and bring it to their mouth. Such a precaution was introduced to be sure that people chewed and swallowed the foods, while they were smelling the odor. The device was contained in a box that was hidden from the participant's view.

The participants were informed that after tasting the food they had to rate it along four dimensions (pleasantness, sweetness, saltiness, and bitterness) by means of a 150 mm long visual analog scale (VAS), anchored with the terms "not at all" and "very much." The VAS was presented at the center of a 17′′ PC screen. The participants used the mouse to select the point on the scale that best represented their evaluation. Each food was presented three times for each olfactory condition, for a total of 18 (2 foods × 3 odors × 3 repetitions) samples of food to be evaluated by each participant. The presentation of the food and the odors were completely randomized.

#### Results

The mean participants' judgments along the VASs were submitted to a series of repeated measures ANOVAs for the hedonic dimension of Pleasantness, as well as for the dimensions of Sweetness, Saltiness and Bitterness (belonging to the so-called "basic tastes" of the flavor network; see Spence et al., 2014; Spence, 2016) with the within-subjects factors of Odor (chocolate vs. citrus), Repetition (evaluation 1, evaluation 2, evaluation 3) and Food (sugar candy vs. cracker).

On the dimension of Pleasantness, the analysis revealed significant main effect of Food [F(1, 21) = 7.26; p = 0.014; d = 0.26]. The factor of Repetition [F(2, 42) = 0.70; p = 0.50] and Odor [F(2, 42) = 0.35; p = 0.70], as well as the interaction between Repetition and Odor [F(4, 84) = 0.22; p = 0.93], Repetition and Food [F(2, 42) = 0.07; p = 0.94], and Odor and Food [F(2, 42) = 0.76; p = 0.47], and the interaction between Repetition, Odor and Food [F(4, 84) = 2.10; p = 0.089] did not revealed any significant effect. A post**-**hoc test (Newman–Keuls corrected) on the main effect of Food showed that participants perceived crackers as more pleasant than candies (p = 0.01).

The data analysis on the dimension of Sweetness showed a significant main effect of Odor [F(2, 42) = 5.27; p = 0.01; d = 0.20] and Food [F(1, 21) = 163.28; p < 0.0001; d = 0.87], the interaction between Repetition and Odor [F(4, 84) = 3.10; p = 0.02; d = 0.13] effect size and Repetition and Food [F(2, 42) = 4.27; p = 0.21; d = 0.17]. The main effect of Repetition [F(2,42) = 0.58; p = 0.56], as well as the interaction between Odor and Food [F(2, 42) = 0.93; p = 0.40] and Repetition, Odor and Food [F(4, 84) = 0.23; p = 0.92] did not revealed any significant effect. A Newman-Keuls post-hoc test on the dimension of Odor revealed that partecipants perceived both foods as sweeter when tasted together with chocolate odor, as compared to citrus odor (p = 0.21) and air (p = 0.01; **Figure 4**). A Newman-Keuls posthoc test on the dimension of Food showed that participants, as expected evaluated candies as sweeter than crackers (p = 0.0001).

A Newman-Keuls post-hoc test on the interaction between Repetition and Odor showed that people perceived both foods as sweeter when tasted together with chocolate odor as compared to air (p = 0.001) and citrus odor (p = 0.05) during the third evaluation but not during the previous two (**Figure 5**). The comparison of the first and second evaluations did not show any significant effect. A Newman-Keuls post-hoc test on the interaction between Repetition and Food showed that participants perceived candies as sweeter during the third evaluation, as compared to the first evaluation (p = 0.2). No other significant differences were found.

On the dimension of Saltiness, the analysis revealed a significant main effect of the Food dimension [F(1, 21) = 237.37; p < 0.0001; d = 0.92]. The effect of Repetition [F(2, 42) = 3.13; p = 0.13], Odor [F(2, 42) = 0.92; p = 0.41], as well as the interaction between Repetition and Odor [F(4, 84) = 0.16; p = 0.96], Repetition and Food [F(2, 42) = 1.83; p = 0.17], odor and Food [F(2, 42) = 0.37; p = 0.69] and Repetition, Odor and Food [F(4, 84) = 0.13; p = 0.97] did not show any significant effect. A Newman-Keuls post-hoc test on the Food dimension showed, as expected, that crackers were evaluated as more salty than candies (p < 0.0001).

The data analysis on the dimension of Bitterness, revealed a significant main effect of Food [F(1, 21) = 4.84; p = 0.04; d = 0.19]. The dimension of Repetition [F(2, 42) =1.44; p = 0.25], Odor [F(2, 42) = 0.60; p = 0.55], as well as the interaction between Repetition and Odor [F(4, 84) = 0.39; p = 0.82], Repetition and Food [F(2, 42) = 1.85; p = 0.83], Odor and Food [F(2, 42) = 1.33; p = 0.27], and Repetition, Odor and Food [F(4, 84) = 0.54; p = 0.70] did not showed any significant effect. A Newman-Keuls post-hoc test on the dimension of Food demonstrated, as expected that crackers were evaluated as more bitter than candies (p < 0.04).

tasted regardless of the evaluation sequence, as a function of the different odor conditions. Error bars represent the standard errors of the means. Asterisks represent Newman-Keuls significant differences at \*p < 0.01.

# EXPERIMENT 2

In summary, Experiment 1 revealed that that participants perceived both foods (crackers and candies), as sweeter when presented together with the chocolate odor, as compared to when presented with air or citrus odors. Based on that result, we proceeded with the second experiment to extend our investigation to liquid taste perception.

The aim of Experiment 2 was to test if the experience generated by the odors delivered through our olfactory device could affect people's taste perception of three different types of beverages on a number of hedonic and perceptual-dimensions (such as pleasantness, freshness, sweetness, saltiness, bitterness and carbonation intensity).

#### Materials and Methods Participants

Twenty-seven participants with a mean age of 24.19 years (SD = 3.53, 21 female), took part in the Experiment. All the participants gave informed written consent prior to their participation. The Experiment described here were all performed in accordance with the ethical standards laid down in the 2008 Declaration of Helsinki and approved by the local ethical committee. The Experiment lasted for approximately 20–30 min. People who claimed to be affected by any permanent or temporary olfactory or taste dysfunction were excluded from taking part in the Experiment.

#### Stimuli

Three different types of beverages were used: sparkling mineral water, tonic water and Sprite R . Common transparent plastic cups were used to serve the liquids. The beverages were selected on the basis of the same rationale of Experiment 1 with the additional characteristic to be all three transparent (to avoid the colorrelated effect on taste perception). The two odors administered were the same of Experiment 1 (chocolate and a mixture of citrus fruit, manufactured by Oikos Fragrances R ).

#### Procedures

Before the beginning of the experiment, a short pre-test was performed to evaluate people's ability to perceive the odors by means the experimental device. The study was conducted in an experimental booth.  The participants were instructed to grasp the plastic cup and taste the beverage served in it at a signal of the experimenter, while at the same time they smelled an odor or clear air administered to both nostrils for about 6 s. The timing of Experiment 2 differed from that adopted in Experiment 1 (<9 s) given that the act of drinking a sip of a beverage is very fast, as compared to the act of taste a solid food. Therefore, if the experimenter had asked to the participants to hold the liquid in their mouth for a time that exceeded the normal act of tasting a beverage, the results could have been distorted. Specifically, following a number of pre-tests a time of 6 s was given to the participants to keep the liquid in their mouth. Longer intervals were in fact considered excessive (and lead to boredom) for the participants. The procedure of odor delivery was completely identical to that of Experiment 1, as well as the fact that the olfactometer was not visible to the participants. The participants were also informed that after tasting the liquid they had to rate it along five dimensions (pleasantness, sweetness, saltiness, bitterness and carbonation intensity) by means of a 150 mm long visual analog scale (VAS), anchored with the terms "not at all" and "very much." The VAS was presented at the center of a 17′′ PC screen. The participants used the mouse to select the point on the scale that best represented

their evaluation. Each liquid was presented three times for each olfactory condition, for a total of 27 (3 beverages × 3 odors × 3 repetitions) samples of liquid to be evaluated by each participant. The presentation of the beverages and the odors was completely randomized.

#### Results

The mean participants' judgments along the VASs were submitted to a series of repeated measures ANOVA with the within-subjects factors of Odor (chocolate vs. citrus), Repetition (evaluation 1, evaluation 2, evaluation 3) and Beverage (Sparkling Water, Tonic Water, Sprite R ) for the hedonic dimension of Pleasantness, as well as for the dimensions of Sweetness, Saltiness, Bitterness and Carbonation Intensity. The results of the analysis on the dimension of Pleasantness revealed a significant effect of Beverage [F(2, 52) = 16,06; p < 0.0001; d = 0.38] and Repetition [F(2, 52) = 6.16; p = 0.00; d = 0.19]. The main effect of Odor [F(2, 52) = 0.32; p = 0.73], as well as the interaction between Odor and Beverage [F(4, 104) = 0.91, p = 0.46] the interaction between Odor and Repetition [F(4, 104) = 0.65; p = 0.63], the interaction between Beverage and Repetition [F(4, 104) = 0.58, p = 0.68] and the interaction between Repetition, Odor and Beverage [F(8,208) = 1.58, p = 0.13] did not result to be significant. That is, the odors presented did not modulate the participants' perception of pleasantness. A Newman–Keuls corrected post-hoc test on the main effect of Beverage revealed that participants evaluated Sprite R as more pleasant, as compared to Tonic Water (p < 0.000) and sparkling mineral water (p < 0.000). A Newman– Keuls post-hoc test on the main effect of Repetition showed that people regardless of the odors administered found all beverages as more pleasant during the first evaluation, as compared to the second evaluation.

The analysis on the dimension of Sweetness revealed a significant main effect of Odor [F(2, 52) = 3.99; P = 0.24; d = 0.13], Beverage [F(2, 52) = 51.82; p < 0.000; d = 0.67], and Repetition [F(2, 52) = 6.27; p < 0.01; d = 0.19]. A posthoc test (Newman–Keuls) on the main effect of the Odor showed that participants found all the beverages as sweeter when tasted simultaneously with the chocolate odor than when tasted together with the citrus odor (p = 0.03; **Figure 6**). A Newman– Keuls post-hoc test on the main effect of Beverage revealed, as expected, that people perceived Sprite R as sweeter with respect Tonic Water (p < 0.000) and sparkling water (p < 0.000). A Newman–Keuls post-hoc test on the main effect of Repetition showed that participants found all the beverages as sweeter during first evaluation, as compared to the second (p = 0.00) and third (p = 0.01) evaluation.

The results of the analysis of Saltiness showed a significant main effect of Beverage [F(2, 52) = 6.34; p = 0.00; d = 0.20] and of Repetition [F(2, 52) = 3.11; p = 0.05; d = 0.11]. The main effect of odor [F(2, 52) = 2.37; p = 0.10], the interaction between Odor and Beverage [F(4, 104) = 1.42; p = 0.23], the interaction between Odor and Repetition [F(4, 104) = 0.77; p = 0.54], the interaction between Beverage and repetition [F(4, 104) = 0.21; p = 0.93] and the interaction between Odor, Beverage and Repetition [F(8, 208) = 1.92; p = 0.25] did not showed any significant effect. A post-hoc test (Newman–Keuls) on the main effect of

the Beverage revealed that as expected, people perceived Sprite R as less salty than Tonic Water (p = 0.01) and sparkling water (p = 0.01). A post-hoc test (Newman–Keuls) on the main effect of the repetition showed that all the beverages were perceived as more salty during the first evaluation, as compared to the third evaluation (p = 0.04).

The analysis performed on the Bitterness dimension revealed a significant main effect of Beverage [F(2, 52) = 38.60; p < 0.0001; d = 0.60]. The dimension of Odor [F(2, 52) = 0.82; p = 0.44], Repetition [F(2, 52) = 1.25; p = 0.30], as well as, the interaction between Odor and Beverage [F(4, 104) = 0.86; p = 0.49], Odor and Repetition [F(4, 104) = 0.50; p = 0.74], Beverage and Repetition [F(4, 104) = 1.02; p 0.40] and the interaction between Odor, Beverage and Repetition [F(8,208) = 1.37; p = 0.21] did not show any significant effect. A newman-Keuls post-hoc test on the main effect of Beverage revealed that as expected, participants perceived Tonic Water as more bitter than sparkling water (p < 0.001) and Sprite R (p < 0.001).

The results regarding the Carbonation Intensity dimension revealed a significant main effect of Beverage [F(2, 52) = 8.30; p = 0.00; d = 0.24]. The main effect of Odor [F(2, 52) = 0.27; p = 0.77], Repetition [F(2, 52) = 0.74; p = 0.48], as well as, the interaction between Odor and Beverage [F(4, 104) = 0.83; p = 0.51], Odor and Repetition [F(4, 104) = 0.46; p = 0.71], Beverage and Repetition [F(4, 104) = 0.41; p = 0.80 and the interaction between Odor, Beverage and Repetition [F(8,208) = 0.83; p = 0.57] did not revealed any significant effect. A newman-Keuls post-hoc test on the main effect of Beverage revealed that people perceived sparkling water as less carbonated than Tonic Water (p = 0.16) and Sprite R (p = 0.001).

#### DISCUSSION

The results of the present study suggest that odors administered by means our olfactory device can alter people's experience of food, just as it occurs in natural multisensory environments. Moreover, the present study also suggests that the device used to deliver the essences is highly manageable in a laboratory setting. In fact, the possibility to interconnect the olfactometer with the behavioral research software EPrime 2 and to interact with other devices connected to it, allows the implementation of sophisticated experiments in the field of psychology and cognitive neuroscience. With the aid of such device we were able to show multisensory interactions on food perception that are similar to those occurring without the mediation of a HCI device (e.g., when an odor perceived orthonasally affect the taste of the food in the mouth; Borowsky, 1987).

In particular, the results of Experiment 1 showed that participants perceived both foods (crackers and candies), as sweetest when presented together with the chocolate odor, as compared to when presented with air or citrus odors. In Experiment 2, the participants perceived all the beverages (Sparkling Water, Tonic Water, and Sprite), as sweetest when presented together with the chocolate odor, as compared to when presented with citrus odor regardless of the evaluation sequence. That is, the olfactory stimuli delivered by means of the new olfactory display showed to be effective in modulating people's evaluation of food and beverages.

The experimental results demonstrated for the first time that the orthonasal integration of an odor by means our device could affect people's food taste evaluations without adding any additional ingredient to the food. Intriguingly, this is an unusual result concerning a number of claims regarding orthonasal crossmodal integration between food and odors. In fact, it has been previously suggested that, while retronasal integration (e.g., when the odorant contained in food molecules reaches the back of the nose through eating or drinking) should modulate food flavor perception (i.e., sweetness or saltiness), orthonasal integration (e.g., when odor is smelled directly by the nostrils) should only modulate the hedonic dimension (i.e., pleasantness) of food evaluation (see Spence, 2016, for a detailed review). It is, however, worth noting that, despite the fact that during the experiments the olfactory stimulation was orthonasal, some chemical molecules may have somehow reached the oral cavity, and may have been processed also via the retronasal route. Such a possibility, raise the question of how to obtain a pure measure of orthonasal integration between odors and foods under experimental conditions. Future research should be directed to shed light on this issue.

The experimental results reported here are fully consistent with those by Stevenson et al. (2011). These authors demonstrated that the taste intensity ratings of a sweet solution could be significantly enhanced by the concurrent orthonasal presentation of an odor. Interestingly, Stevenson et al.'s results were found while participants tasted a solution, while we showed similar results both for foods and beverages. It is possible that the high precision of the computerized control of the odors administration timing of the MFOD (the latency from generation to perception of a selected odor is <0.5 s, with a length of the delivery pipe of 600 mm) is at the basis of the result found (the presence of orthonasal crossmodal integration). That is, the device used in this paper might have allowed better management of the technical procedures and precision of stimulus delivery, necessary for this kind of studies (although our previous considerations about a retronasal interaction may also be applied here; see the previous paragraph).

Intriguingly, our results have shown that people perceived both foods as sweetest when tasted together with the simultaneous administration of chocolate odor, as compared to air or citrus odors only during the third evaluation and not during the first or the second one. One possible interpretation of this result is that after the first two tasting sessions, food habituation may have occurred. That is, a reduced activation of taste receptors due to habituation (Poellinger et al., 2000) could have amplified the modulatory effect exert by the olfactory stimuli presented by means of the device (i.e., the weaker the taste, the stronger the effect produced by olfaction). This hypothesis should certainly be verified by means of further studies.

As far as the modulation of beverage perception by the device is concerned, it is worth noting that the majority of previous works failed to create the sensation of tasting "virtual beverages" (via the internet) by means of electrical and thermal stimulation (Lant and Norman, 2017; Ranasinghe et al., 2017). One of the reasons for these failures might be due to the lack of a simultaneous chemical stimulation by means odors (using olfactory devices). Since odors represent a pivotal component of taste perception, it would be then interesting to try to use our device also under similar conditions of stimulus presentation (i.e., virtual tasting).

Importantly, no modulatory effects were found on the dimensions of Pleasantness, Bitterness, Saltiness, and Carbonation Intensity. As far as this negative result is concerned, it should be considered that the more or less explicit perception by the participants that the context of stimulus presentation was artificially manipulated (e.g., that the odor did not arise from the beverage itself), could have made more difficult the integration between the olfactory and gustative qualities of the drinks (cf. Dietrich, 2006). Alternatively, it is possible that during Experiment 2 participants experienced a greater difficulty to achieve the temporal and spatial coincidence (Spence, 2011) needed to integrate taste and olfactory stimulation. In fact, also because of the risk of choke, people cannot swallow and sniff from the nostrils at the same time. Interestingly, in Stevenson et al. (2011) experiments, participants held the solution to be tasted in their mouth while smelling the odors through the nostrils, perhaps with the specific aim to achieve this important condition of sensory integration. Note, however, that this procedure likely reduces the ecological validity of the study, given that it is not a natural procedure adopted by people when they are drinking liquids.

In Experiment 2, differently from Experiment 1, no interactive effects were found among repetitions and odors. This result suggests that the tastings sequence did not modulate people's beverages evaluations. This result would seem to suggest that orthonasal crossmodal integration of odors and taste at the basis of people evaluation, might somehow differ, as a function of the gustatory experience involved (foods or beverages). Future research should be addressed to better comprehend the mechanisms at the basis of this difference.

Importantly, the small size and weight of the device presented in this paper (size Height 40 cm, Width 40 cm, Length 50 cm, and Weight <2 kilos) makes it easily adaptable in laboratory and even in more ecological contexts than other olfactory systems. The olfactometers used so far in research laboratories are difficult to be handled, extremely complex during the experimental managing, rather cumbersome and extremely expensive.

The results of Experiment 1 and 2 are in line with previous scientific evidence showing that people's perception of food and beverages can be altered by the multisensory context where the stimuli are presented (Zampini and Spence, 2005; Stevenson et al., 2011; Piqueras-Fiszman et al., 2012; Maggioni et al., 2015; Risso et al., 2015). In fact, despite of the fact that the participants knew that the odor did not originate from the food itself, their evaluation was still significantly affected by it. As far as this point is concerned, our results are the first to show an orthonasal interaction between taste and odor in people's evaluation of food and beverages sweetness by using a small size olfactory interface.

Our results may also be interpreted in terms of a "halo dumping" enhancement effect caused by the sweet quality of chocolate odors. That is, the sweetness of the odors "drove" people's judgments of taste. However, such an evaluative bias was previously found by retronasal perception only and in an unaware condition of stimulus presentation (Green et al., 2012). By contrast, in the present study, odors presentation was orthonasal, and people were perfectly aware of the nature of odor presentation. Finally, halo dumping is generally a homogeneous effect that involves all the characteristics to be evaluated (Thorndike, 1920). By contrast, our results showed a significant modulation only on the scale of sweetness.

Another possible interpretation concerning to the effect found in our experiments could be referred to the fact that participants could have rated the chocolate odor sweetness, instead of food sweetness. However, it is important to highlight that the presentation of the olfactory stimuli here was orthonasal. For this very reason, people were well aware that beverage and food taste perceptions were separated from odor perception. That is, it is unluckily that the olfactory stimuli delivered by our device were confused with the retronasal perception of the odor molecules contained in the stimuli to be evaluated. That said, it is still possible that the sweet quality of chocolate odor was unconsciously transferred and integrated to food perception, thus influencing the participants in their evaluation. Indeed, often people use verbal expressions that are generally used in taste perception to describe an odor. For example, smells sweet is often used concerning vanilla odor (Auvray and Spence, 2007). It is possible that the confusion generated by the use of this kind of semantic metaphor is at the base of the effects found in the present study. Future studies are needed to further clarify this point (see Gallace et al., 2010, for the semantic associations between words and food).

Further studies should also be addressed at investigating the effects of delivering olfactory stimuli by means of devices, such as that presented here, on the perception of different food and beverages, also under ecologically valid condition of stimulus presentation (e.g., in restaurants). Finally, a series of studies will need to be performed in order to study the effects of delivering odors by means olfactory devices within virtual reality simulations. In particular, it will be interesting to observe how olfactory information contribute to our sense of presence, and what aspects of the stimulation are more relevant to improve this perception (e.g., temporal visuo-olfactory synchrony, spatial position, etc.).

It is important to highlight here that the olfactory stimuli delivered by means of the MFOD consisted of compressed powders. Differently from the solution adopted by the majority of olfactory device commercialized nowadays, such a technical arrangement avoids the use of liquid odorants that requires complex systems in order to balance their dilutions.

It should be mentioned that the device adopted in the present study is a prototype and that further devices (which will allow to deliver up to 20 odors and with a higher degree of miniaturization) are now under development. These new generation of portable olfactometers, will certainly allow a large number of applications, comprising those related to enhancing the sense of presence in virtual reality environments. These devices will also contribute to investigating perceptual, emotional, and retention-related (memory) aspects of olfaction in humans, as well as be part of multisensory rehabilitations techniques for a number of neuropsychological disorders (Atanasova et al., 2008; Baba et al., 2012).

# WEB LINKS

Aroma Shooter, https://aromajoin.com/en/hardware/shooters/ aroma-shooter-mini-1

Scentsory Design https://link.springer.com/content/pdf/10. 1007/978-3-540-79486-8\_32.pdf

Aroma Rainbow Sensitive Dress http://www.escent.ai/ smartsecondskin

Mist Shine Indiegogo, https://www.indiegogo.com/projects/ mist-shine-wearable-smart-scent#/

Swallable Parfum, https://www.lucymcrae.net/swallowableparfum/

E-Prime, www.pstnet.com/eprime.cfm

# AUTHOR CONTRIBUTIONS

PR: Experiment design, Experiment implementation, olfactometer interface with ePrime2, data collection, data analysis, manuscript writing; MC: Olfactometer design, Olfactometer implementation, Olfactometer interface with ePrime2, manuscript writing; MB: Olfactometer design, Olfactometer implementation, Olfactometer interface with ePrime2, manuscript writing, manuscript supervision; AG: Experiment design, Experiment implementation, data analysis, data analysis supervision, manuscript writing, manuscript writing supervision.

## ACKNOWLEDGMENTS

The authors would like to thank the apprentices of the Department of Psychology of Bicocca University for the experimental data collection and the Bicocca University students for their participation in the study.

Frontiers in Digital Humanities | www.frontiersin.org

#### REFERENCES

**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 © 2018 Risso, Covarrubias Rodriguez, Bordegoni and Gallace. 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) and the copyright owner 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.

# Multisensory Technology for Flavor Augmentation: A Mini Review

Carlos Velasco1 \*, Marianna Obrist2 , Olivia Petit3 and Charles Spence4

1 Center for Multisensory Marketing, Department of Marketing, BI Norwegian Business School, Oslo, Norway, 2 Sussex Computer Human Interaction Lab, Creative Technology Research Group, School of Engineering and Informatics, University of Sussex, Brighton, United Kingdom, 3 INSEEC Business School, Paris, France, 4 Crossmodal Research Laboratory, Department of Experimental Psychology, University of Oxford, Oxford, United Kingdom

There is growing interest in the development of new technologies that capitalize on our emerging understanding of the multisensory influences on flavor perception in order to enhance human–food interaction design. This review focuses on the role of (extrinsic) visual, auditory, and haptic/tactile elements in modulating flavor perception and more generally, our food and drink experiences. We review some of the most exciting examples of recent multisensory technologies for augmenting such experiences. Here, we discuss applications for these technologies, for example, in the field of food experience design, in the support of healthy eating, and in the rapidly growing world of sensory marketing. However, as the review makes clear, while there are many opportunities for novel human–food interaction design, there are also a number of challenges that will need to be tackled before new technologies can be meaningfully integrated into our everyday food and drink experiences.

#### Edited by:

Francesco Ferrise, Politecnico di Milano, Italy

#### Reviewed by:

Takuji Narumi, The University of Tokyo, Japan Mehdi Ammi, Université Paris-Sud, France

# \*Correspondence:

Carlos Velasco<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Human-Media Interaction, a section of the journal Frontiers in Psychology

Received: 06 August 2017 Accepted: 09 January 2018 Published: 30 January 2018

#### Citation:

Velasco C, Obrist M, Petit O and Spence C (2018) Multisensory Technology for Flavor Augmentation: A Mini Review. Front. Psychol. 9:26. doi: 10.3389/fpsyg.2018.00026 Keywords: food, multisensory, experience, augmentation, vision, audition, touch, haptics

# INTRODUCTION