# THE METAPHORICAL BRAIN

EDITED BY: Seana Coulson and Vicky T. Lai PUBLISHED IN: Frontiers in Human Neuroscience

### *Frontiers Copyright Statement*

*© Copyright 2007-2016 Frontiers Media SA. All rights reserved. All content included on this site, such as text, graphics, logos, button icons, images, video/audio clips, downloads, data compilations and software, is the property of or is licensed to Frontiers Media SA ("Frontiers") or its licensees and/or subcontractors. The copyright in the text of individual articles is the property of their respective authors, subject to a license granted to Frontiers.*

*The compilation of articles constituting this e-book, wherever published, as well as the compilation of all other content on this site, is the exclusive property of Frontiers. For the conditions for downloading and copying of e-books from Frontiers' website, please see the Terms for Website Use. If purchasing Frontiers e-books from other websites or sources, the conditions of the website concerned apply.*

*Images and graphics not forming part of user-contributed materials may not be downloaded or copied without permission.*

*Individual articles may be downloaded and reproduced in accordance with the principles of the CC-BY licence subject to any copyright or other notices. They may not be re-sold as an e-book.*

*As author or other contributor you grant a CC-BY licence to others to reproduce your articles, including any graphics and third-party materials supplied by you, in accordance with the Conditions for Website Use and subject to any copyright notices which you include in connection with your articles and materials.*

> *All copyright, and all rights therein, are protected by national and international copyright laws.*

*The above represents a summary only. For the full conditions see the Conditions for Authors and the Conditions for Website Use.*

ISSN 1664-8714 ISBN 978-2-88919-772-9 DOI 10.3389/978-2-88919-772-9

# About Frontiers

Frontiers is more than just an open-access publisher of scholarly articles: it is a pioneering approach to the world of academia, radically improving the way scholarly research is managed. The grand vision of Frontiers is a world where all people have an equal opportunity to seek, share and generate knowledge. Frontiers provides immediate and permanent online open access to all its publications, but this alone is not enough to realize our grand goals.

# Frontiers Journal Series

The Frontiers Journal Series is a multi-tier and interdisciplinary set of open-access, online journals, promising a paradigm shift from the current review, selection and dissemination processes in academic publishing. All Frontiers journals are driven by researchers for researchers; therefore, they constitute a service to the scholarly community. At the same time, the Frontiers Journal Series operates on a revolutionary invention, the tiered publishing system, initially addressing specific communities of scholars, and gradually climbing up to broader public understanding, thus serving the interests of the lay society, too.

# Dedication to Quality

Each Frontiers article is a landmark of the highest quality, thanks to genuinely collaborative interactions between authors and review editors, who include some of the world's best academicians. Research must be certified by peers before entering a stream of knowledge that may eventually reach the public - and shape society; therefore, Frontiers only applies the most rigorous and unbiased reviews.

Frontiers revolutionizes research publishing by freely delivering the most outstanding research, evaluated with no bias from both the academic and social point of view. By applying the most advanced information technologies, Frontiers is catapulting scholarly publishing into a new generation.

# What are Frontiers Research Topics?

Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office<EMAIL_ADDRESS>
# **THE METAPHORICAL BRAIN**

Topic Editors: **Seana Coulson,** University of California, San Diego, USA **Vicky T. Lai,** University of South Carolina, USA

Word cloud generated based on the titles and the abstracts from the articles included in this Research Topic via the Tagul website (https://tagul.com)

Metaphor has been an issue of intense research and debate for decades (see, for example [1]). Researchers in various disciplines, including linguistics, psychology, computer science, education, and philosophy have developed a variety of theories, and much progress has been made [2]. For one, metaphor is no longer considered a rhetorical flourish that is found mainly in literary texts. Rather, linguists have shown that metaphor is a pervasive phenomenon in everyday language, a major force in the development of new word meanings, and the source of at least some grammatical function words [3]. Indeed, one of the most influential theories of metaphor involves the suggestion that the frequency of metaphoric language results because cross-domain mappings are a major determinant in the organization of semantic memory, as cognitive and neural resources for dealing with concrete domains are recruited for the conceptualization of more abstract ones [4]. Researchers in cognitive neuroscience have explored whether particular kinds of brain damage are associated with metaphor production and comprehension deficits, and whether similar brain regions are recruited when healthy adults understand the literal and metaphorical meanings of the same words (see [5] for a review). Whereas early research on this topic focused on the issue of the role of hemispheric asymmetry in the comprehension and production of metaphors [6], in recent years cognitive neuroscientists have argued that metaphor is not a monolithic category, and that metaphor processing varies as a function of numerous factors, including the novelty or conventionality of a particular metaphoric expression, its part of speech, and the extent of contextual support for the metaphoric meaning (see, e.g., [7], [8], [9]). Moreover, recent developments in cognitive neuroscience point to a sensorimotor basis for many concrete concepts, and raise the issue of whether these mechanisms are ever recruited to process more abstract concepts [10].

This Frontiers Research Topic brings together contributions from researchers in cognitive neuroscience whose work involves the study of metaphor in language and thought in order to promote the development of the neuroscientific investigation of metaphor. Adopting an interdisciplinary perspective, it synthesizes current findings on the cognitive neuroscience of metaphor, provides a forum for voicing novel perspectives, and promotes avenues for new research on the metaphorical brain.

# **REFERENCES**

**Citation:** Coulson, S., Lai, V. T., eds. (2016). The Metaphorical Brain. Lausanne: Frontiers Media. doi: 10.3389/978-2-88919-772-9

# Table of Contents

*144 Auditory and motion metaphors have different scalp distributions: An ERP study*

Gwenda L. Schmidt-Snoek, Ashley R. Drew, Elizabeth C. Barile and Stephen J. Agauas

*153 Action verbs are processed differently in metaphorical and literal sentences depending on the semantic match of visual primes*

Melissa Troyer, Lauren B. Curley, Luke E. Miller, Ayse P. Saygin and Benjamin K. Bergen

*169 How vertical hand movements impact brain activity elicited by literally and metaphorically related words: an ERP study of embodied metaphor* Megan Bardolph and Seana Coulson

# Editorial: The Metaphorical Brain

Seana Coulson1 \* and Vicky T. Lai 2

1 Cognitive Science Department, University of California, San Diego, La Jolla, CA, USA, 2 Department of Psychology, University of South Carolina, Columbia, SC, USA

Keywords: Alzheimer's disease, autism, embodiment, executive function, figurative language comprehension, hemispheric specialization, right hemisphere damage, schizophrenia

**The Editorial on the Research Topic**

### **The Metaphorical Brain**

Long considered a peripheral topic in linguistics, metaphor is increasingly viewed as a central feature of higher cognition and abstract thought. Investigation of the neural substrate of metaphor has, similarly, become more sophisticated, involving increasingly specific suggestions about the processes involved in its comprehension. This Frontiers Research Topic brings together contributions from a diverse array of cognitive neuroscience to offer a snapshot of current research on the neural substrate of figurative language, and present a number of avenues for future research. The result is an interdisciplinary perspective on the differences between literal and figurative language and how the underlying neurobiological processes can be investigated.

Indeed, most investigations into the neural substrate of metaphor ultimately concern the relationship between literal and metaphorical meanings. In their excellent review paper, Vulchanova and colleagues outline the arguments for and against the continuity thesis that literal and metaphorical language comprehension recruits essentially the same processing mechanisms. Using autism as a lens through which to consider the issue, they review data that indicate dissociations in the comprehension of literal and figurative language within individuals with ASD. Ultimately, they suggest figurative language deficits in ASD stem from the difficulty these individuals have integrating contextual information to build the situation model.

One source of support for the idea that literal and metaphorical comprehension processes recruit distinct neural substrates is the increasingly contentious claim that the right cerebral hemisphere (RH) plays a crucial role in the comprehension of metaphor, but not literal language. Ianni and colleagues note that much of the data supporting this claim comes from the study of brain-injured patients that have employed sub-optimal tasks for assessing metaphor comprehension. They present a novel test with fine-grained sensitivity to participants' ability to understand both literal and metaphorical language. They present data from three patients to demonstrate (i) comparable impairment on literal and metaphorical language, (ii) greater impairment for metaphorical than literal language, and (iii) selective impairment on metaphorical language.

Addressing the issue of hemispheric specialization in healthy adults, Lai and colleagues examine functional neuroimaging data as participants read literal and metaphorical sentences with varying degrees of familiarity. They found that decreasing familiarity (i.e., increasing novelty) of both literal and metaphorical language led to greater activation bilaterally, with more extensive recruitment of LH brain regions overall. However, the relative contribution of the RH was greater for novel metaphors, as a result of reduced LH activation for novel literal language.

Faust and colleagues utilize network theory in their discussion of hemispheric specialization for metaphor comprehension. In particular, they suggest that the LH exhibits semantic rigidity, manifested by networks in which each node is connected to a small number of other nodes. Rigid networks are well suited for the rapid retrieval of conventional meanings, but ill-suited for creating meanings needed for novel metaphors. The RH exhibits semantic chaos, manifested by highly

### Edited and reviewed by:

Hauke R. Heekeren, Freie Universität Berlin, Germany

#### \*Correspondence: Seana Coulson<EMAIL_ADDRESS>
Received: 03 September 2015 Accepted: 11 December 2015 Published: 05 January 2016

### Citation:

Coulson S and Lai VT (2016) Editorial: The Metaphorical Brain. Front. Hum. Neurosci. 9:699. doi: 10.3389/fnhum.2015.00699 inter-connected networks that enable fast connections between semantically distant concepts. Although inter-connectivity facilitates the comprehension of novel metaphors, its pathological extreme can be seen in schizophrenia and accompanying thought disorder.

Mashal and colleagues examined brain activity as schizophrenics and age-matched controls read literal phrases, conventional metaphors, and novel metaphors. They find novel metaphors elicited greater activity in the RH precuneus and superior parietal lobule (SPL) among schizophrenics than controls, and that greater activation in this brain region was correlated with better comprehension. In keeping with Faust and Kennet's suggestion that schizophrenia is associated with greater inter-connectivity in the semantic network, Mashal and colleagues found patients showed a greater degree of functional coupling between the precuneus/SPL and other language regions.

As is typical of studies of metaphor comprehension in schizophrenia, Mashal and colleagues found evidence for reduced comprehension in patients relative to controls. However, figurative language is diverse, and requires multiple mechanisms for its comprehension. Cognizant of this fact, Pesciarelli and colleagues investigated whether patients with schizophrenia can utilize both combinatorial mechanisms and the retrieval of stored meanings in their comprehension of idioms. They report evidence suggesting that the difficulty schizophrenic patients have understanding metaphors is less pronounced in the case of idioms for which they can rely on the retrieval of stored meanings.

Differences between the processing of metaphors and idioms are also supported by studies of healthy adults. Columbus and colleagues asked whether domain-general aspects of executive control influenced reading times for familiar and unfamiliar metaphorical sentences and idioms. They found that individuals with high executive control utilized context more efficiently than those with low executive control to commit to a metaphorical or literal reading of a target word. While executive control led to advantages for both familiar and unfamiliar metaphors, all participants read idioms efficiently, reinforcing the importance of retrieval mechanisms for idiom comprehension.

Metaphor comprehension is also impacted by individual differences in abstraction ability. Roncero and de Almedia examined figurative language processing in individuals with Alzheimer's disease (AD). In two studies they explored whether patients' abstraction ability was related to how well they interpreted metaphors, and whether saliency as measured by aptness ratings as well as familiarity ratings influenced patients' metaphor interpretation scores. Their findings suggest that patients with better abstraction ability produced better interpretations, and that aptness, not familiarity predicted patients' metaphor interpretation ability.

Other investigators have examined the importance of concreteness on understanding metaphors. Forgács and colleagues compared ERPs to nouns in phrases that were metaphorical (fluffy speech), concrete literal (nasal speech), and abstract literal (ineffective speech). Whereas, adjectives in literal phrases elicited typical ERP concreteness effects, nouns in metaphorical phrases did not. Paradoxically, when the novel metaphorical phrases were rated more concrete, the ERPs to the target nouns resembled those to nouns in abstract literal phrases. When the novel metaphorical phrases were rated more abstract, the ERPs to target nouns resembled those to nouns in concrete literal phrases. Results are argued to support a model in which the literal meaning from the concrete source domain in a metaphor is abstracted away from its physical sense before it is mapped to the abstract target domain.

Weiland and colleagues examined the priority of literal meaning during the processing of metaphor and metonymy. In this study, the literal meaning of the target expressions (e.g., These lawyers are hyenas) was induced via a briefly presented prime (furry) prior to the target (hyenas). At the target word they observed a reduction in the early ERP effect for both metaphors and metonymies and a delay in the late ERP effect only for metaphors. They suggested that the induced literal meaning facilitated the first stage of metaphor comprehension, which involves its literal sense.

Lakoff, in a theoretical contribution, outlined in brief his influential approach to metaphor, describing the existence of systematic metaphors in language, and arguing that they reflect regularities in the conceptual system, that are in turn driven by experiential correlations encoded neurally via spike timing dependent plasticity. Lakoff details empirical support for his theory that stems from linguistics, psychology, and cognitive neuroscience. He dispels some unflattering and oversimplified readings of his account, and sketches the beginnings of a neural theory of metaphor.

Lakoff's call for further research is taken up by a number of other contributors to the volume. These researchers present original research testing some of the predictions of embodied metaphor theory, and its more general counterpart in embodied cognition. For example, Schmidt-Snoek and colleagues compared the event related brain response to metaphors whose source domain evoked the auditory modality, as in "Her limousine was a privileged snort," or the motor modality, as in "The editorial was a brass-knuckle punch," and literal uses of the same words. They found that auditory words elicited a slightly different pattern of ERPs than did motor words, suggestive of non-overlapping neural generators. These findings fit with predictions from embodied metaphor theory that modality specific activations contribute to both literal and metaphoric meanings of these words.

Troyer and colleagues examine whether videos and still images of point light walkers impact reading times for sentences with action verbs. As one might expect from embodied models of cognition, the perception of visual motion does impact the processing of sentences with action verbs, but does so differently for literal uses, such as "The chemist was walking to his lab," and metaphorical ones, such as "The company was walking to its death."

Similarly, Bardolph and Coulson recorded ERPs as participants read words associated with different regions of vertical space as they moved marbles in an upward or a downward directed motion. Words such as "floor" and "ceiling" elicited very early congruency effects in the ERPs, consistent with the involvement of motor regions in registering the conflict between meaning and motion. Words such as "defeat" and "victory," whose vertical associations were metaphorical, elicited congruency effects that emerged much later, in keeping with a role in pragmatic inference.

By focusing on novel research on the neural basis of metaphor, this Frontiers Research Topic provides insight into the neurobiology of conceptual structure. The contributions highlight how metaphor comprehension reveals hemispheric differences in the organization of semantic memory, the importance of executive function for high-level language comprehension, and the differing roles of sensorimotor activations for concrete and abstract concepts. Beyond the individual contributions, we hope that this special focus will inspire future research on the neural underpinnings of metaphor in language, and metaphor in cognition more generally.

# AUTHOR CONTRIBUTIONS

Both authors contributed equally to the writing and editing of this review article.

# FUNDING

SC received support from the Kavli Institute for Brain & Mind, San Diego.

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

Copyright © 2016 Coulson and Lai. 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.

#### **Mila Vulchanova1\*, David Saldaña2 , Sobh Chahboun1 and Valentin Vulchanov1**

1 Language Acquisition and Language Processing Lab, Department of Language and Literature, Norwegian University of Science and Technology, Trondheim, Norway

2 Individual Differences, Language and Cognition Lab, Department of Developmental and Educational Psychology, University of Seville, Seville, Spain

#### **Edited by:**

Seana Coulson, University of California at San Diego, USA

#### **Reviewed by:**

Christelle Declercq, Université de Reims Champagne-Ardenne, France Valentina Bambini, Institute for Advanced Study (IUSS), Italy

#### **\*Correspondence:**

Mila Vulchanova, Language Acquisition and Language Processing Lab, Department of Language and Literature, Norwegian University of Science and Technology, Edvard Bulls veg 1, 7491 Trondheim, Norway e-mail<EMAIL_ADDRESS>
This paper is intended to provide a critical overview of experimental and clinical research documenting problems in figurative language processing in atypical populations with a focus on the Autistic Spectrum. Research in the comprehension and processing of figurative language in autism invariably documents problems in this area. The greater paradox is that even at the higher end of the spectrum or in the cases of linguistically talented individuals with Asperger syndrome, where structural language competence is intact, problems with extended language persist. If we assume that figurative and extended uses of language essentially depend on the perception and processing of more concrete core concepts and phenomena, the commonly observed failure in atypical populations to understand figurative language remains a puzzle. Various accounts have been offered to explain this issue, ranging from linking potential failure directly to overall structural language competence (Norbury, 2005; Brock et al., 2008) to right-hemispheric involvement (Gold and Faust, 2010). We argue that the dissociation between structural language and figurative language competence in autism should be sought in more general cognitive mechanisms and traits in the autistic phenotype (e.g., in terms of weak central coherence, Vulchanova et al., 2012b), as well as failure at on-line semantic integration with increased complexity and diversity of the stimuli (Coulson and Van Petten, 2002). This perspective is even more compelling in light of similar problems in a number of conditions, including both acquired (e.g., Aphasia) and developmental disorders (Williams Syndrome). This dissociation argues against a simple continuity view of language interpretation.

**Keywords: figurative language, autism spectrum disorders, metaphors, idioms, impaired processing mechanisms**

### **INTRODUCTION**

Figurative language is a cover term for linguistic expressions whose interpretation is nonliteral, where the meaning of the expression as a whole cannot be computed directly from the meaning of its constituents. Figurative language can vary in types, degrees of extension from the literal and degrees of transparency, and structure. Moreover, figurative expressions can fluctuate from a single word to a long sentence. Here belong a range of phenomena, such as metaphors, idioms, proverbs, humor and jokes, hyperbole, indirect requests, clichés (Gibbs, 1999). Such expressions are characterized by interpretations which cannot be retrieved by simply knowing the basic senses of the constituent lexical items, and where the addressee needs to arrive at the intended meaning rather than what is being said literally.

It has been claimed that it is exactly the need to go beyond the literal interpretation and grasp the intended meaning that makes figurative language special and more demanding for processing (Levorato and Cacciari, 2002). Unlike literal language, such expressions depend more heavily on both linguistic and visual context, and are often—in fact, impossible—to understand in the absence of such context. Still, in everyday communication much of the meaning is implied, and can be understood following linguistic and contextual cues (Coulson, 2005). It is this context sensitivity of natural language that has inspired the continuity claim that figurative language is not exceptional. From this perspective, all language and all its sentences are multiply ambiguous whereby the content of all utterances largely underdetermines their interpretation (Gibbs, 1994; Sperber and Wilson, 2006). This approach suggests that figurative language is rather to be found on a continuum from literal-to looseto metaphorical language and should not be considered as a departure from normal language use. While this is one of the more radical interpretations, all approaches arguing for a lack of exceptionality in figurative language sustain that it is pervasive both in language and in thought (Fauconnier, 1997, 2007; Lakoff and Johnson, 1980; Lakoff, 1987; Turner, 1991). If this is true, then it is not a special form of language.

Yet, research in developmental disorders documents subtle dissociations between the ability to understand literal expressions and the comprehension of nonliteral (figurative) language. For instance, high-functioning individuals with autism with intact structural language skills often fail to understand the meaning of jokes, irony, and idiomatic language (Gold and Faust, 2010; Vulchanova et al., 2012a,b). Thus, they present a case against a simple continuum view of figurative language.

In this paper we present evidence from studies of figurative language processing in autism arguing that this evidence calls for a revision of a simple continuum view. We first review issues of relevance to our main topic, such as how to best approach and understand the similarities and differences in the processing of literal and figurative language. For this purpose we start by discussing evidence from typically developing children and adults, to then move on to comment on the data that can be found in looking at a population of special interest to figurative language, namely individuals with autism. We conclude by suggesting possible ways in which these data can be interpreted in the light of current cognitive accounts of autism and more broader approaches to language comprehension.

### **FIGURATIVE LANGUAGE IN TYPICAL POPULATIONS FIGURATIVE LANGUAGE ACQUISITION IN TYPICAL DEVELOPMENT**

Language development provides evidence of the somewhat different status of figurative language. It takes more time for children to begin to appreciate extended uses. According to Nippold (2006), the development of skills in processing metaphors, idioms and proverbs is an important part of semantic development. Compared to vocabulary acquisition and basic semantic skills, skills in the domain of figurative language emerge later. Thus, recent research (Levorato and Cacciari, 1995; Nippold, 1998, 2006; Kempler et al., 1999; Nippold and Duthie, 2003; Cain et al., 2009) suggests that the acquisition of idioms takes longer than vocabulary acquisition, and that it gradually takes off after age five and on.

Opinions, and findings, however, divide concerning the path of this development. Nippold (1998, 2006) and Nippold and Duthie (2003) assume that this is a gradual development, not essentially different from other lexical development, and that it continues also in adulthood. However, Kempler et al. (1999) show that the understanding of idioms follows a non-linear path, very similar to the vocabulary burst between the second and the third year (Marchman and Bates, 1994; Bates and Goodman, 1997). Unlike vocabulary, however, with idioms, this process takes approximately four times longer, with a peak at around 11 years (Vulchanova et al., 2011). In a study of 6- and 9-year-old children and adults, Laval and Bernicot (2002) provide evidence that only at age 9 can children start to appreciate and use context in idiom comprehension. Furthermore, only from this age on children show sensitivity to frequency and familiarity.

The appreciation of figurative language in development requires coordination between cognitive, linguistic and pragmatic skills (Tolchinsky, 2004; Bernicot et al., 2007). Several factors play a role in the acquisition and comprehension of figurative language. Among the most salient ones for idioms, for instance, are frequency of the expression, transparency of its structure, the context in which it is encountered, and linguistic skills and competences (Nippold and Duthie, 2003). It is commonly agreed and has been demonstrated that metalinguistic awareness facilitates the understanding of figurative language, including idioms (Levorato and Cacciari, 2002; Nippold and Duthie, 2003; Nippold, 2006). It has also been shown that reading comprehension is a strong predictor of idiom comprehension (Levorato et al., 2004).

Bernicot et al. (2007) investigated the order of acquisition of different types of nonliteral language in children. They studied the relationship between the children's understanding and their meta-pragmatic competence, defined as the ability to distinguish between what is being said and what is meant in indirect language. In that study they looked at three different types of expressions: indirect requests, idioms and conversational implicatures, in a story completion task. Their results demonstrate that mastering advanced language skills and competencies, such as those required for figurative language processing, correlates with age. This may be attributed to the maturity needed for the processing of expressions offering increased complexity of the inference between the literal meaning (what we say) and the figurative one (what we mean).

# **ACCOUNTS OF FIGURATIVE LANGUAGE PROCESSING Metaphors and literal language**

Metaphors are by far the most "popular" paradigmatic example of figurative language. At the level of thought, conceptual metaphor is a cognitive process by which we represent an abstract concept in terms of a more concrete and tangible one. Metaphors establish (novel) links or mappings between mental domains or spaces, typically a source one and a target one (Fauconnier, 1985). As such, they are ways of thinking capturing generalizations about the world around us and our experience of it.

Theories of metaphors differ in how they assume metaphors are processed, and whether they consider them a departure from normal (literal) language or not. The standard pragmatic view assumes that metaphors are expressions processed via mechanisms different from those used for literal meanings. On this view, the literal meaning should be accessed and rejected before arriving at the intended (figurative) meaning. This implies that an inference is necessary to access the appropriate intended meaning (Grice, 1975). Many authors consider metaphors as "special" structures which are present in everyday language and change depending on time and culture (Lakoff and Johnson, 1980; Turner, 1991).

Alternatively it is suggested that metaphorical and literal meanings are processed in parallel and also use the same mechanisms (Gibbs, 1994). Thus, for both lexical items and metaphorical language, processing interacts with information retrieved from the context (Gibbs, 1987, 1994). Gibbs et al. (1997) found that metaphors did not require more time to process than literal expressions. Furthermore, reaction times did not differ when the context was adequate. An important caveat here is, that equivalent processing times need not reflect equivalent effort (Coulson and Van Petten, 2002; Bambini and Resta, 2012).

Coulson and Van Petten (2002) point to evidence from processing studies suggesting that metaphoric language places heavier demands on processing and requires additional effort for alignment and inference than literal language, not in the least by placing additional demands on working memory (Blasko, 1999). They further argue that the continuity claim should be distinguished from the equivalence claim, which assumes that metaphoric language is no more difficult to comprehend than literal language. They adopt a conceptual blending approach to metaphor (Fauconnier and Turner, 1998), which explains metaphor comprehension as a dynamic process, which creates a blending space combining attributes from the source and target domains. Thus, interpretation arises as a result of selecting relevant properties of these domains and inhibiting aspects which are not relevant through a process of constant updating. In an ERP study, which tested three types of expressions, sentences that ended with words used literally, metaphorically and in an intermediate literal mapping condition, they document that metaphors elicit the greatest N400 effect, while literal mappings occupy a place between true metaphors and literal statements judging by brain responses. This study thus provides evidence for the continuity claim, and, at the same time, shows that metaphors are indeed more demanding for processing, but in a gradient way. The authors suggest that metaphor "taxes" the system we use to understand figurative meaning for two basic reasons. On the one hand, one needs to establish a mapping between elements in distantly related domains (e.g., unlike metonymy), and on the other, to retrieve information from memory to integrate these elements. Other studies have shown similar results (Pynte et al., 1996).

A common problem in assessing results from research in figurative language processing, as observed in Pickering and Frisson (2001), is that word frequency, plausibility, and cloze probability have not always been controlled in several studies reporting reading times for literal and figurative language. Such variables should be taken into account and would have produced different results when determining whether figurative language is more demanding compared to literal language.

Links between metaphors and other types of figurative expressions have been suggested. Gibbs (2003) argues that idioms, often considered as "dead" metaphors, in fact, offer a more dynamic metaphor-based processing. In another study, Gibbs et al. (1997) conducted a series of experiments using a priming method to investigate the role of conceptual metaphors in immediate idiom integration. The aim of the study was to establish whether conceptual metaphors were accessed faster in the context of idioms in discourse. Participants accessed conceptual metaphors more often for the purpose of understanding an idiom, and less so when they were processing literal expressions or literal paraphrases of idioms. Furthermore, this study demonstrated that people access the appropriate conceptual metaphor when they are integrating each specific idiom, and not a similar one with the same figurative meaning. This suggests that idioms with the same figurative meanings may be associated with different conceptual metaphors.

### **Processing of idiomatic expressions**

As a form of nonliteral language, idioms have attracted attention both in theoretical linguistics and in empirical psycholinguistic research, as a result of their specific nature, both in terms of structure and organization. Unlike regular phrases and expressions, idioms come largely in a "prepackaged" form, with many, if not all of their components which cannot be freely replaced or supplemented. Idioms are expressions of varying degree of frozenness and semantic transparency. On the one hand, they are retrieved from the lexicon because they have to be acquired and stored like lexical items, and, on the other, they are processed like structures generated by grammar (Jackendoff, 2002; Vulchanova et al., 2011). Due to this "double" nature or different levels of processing, understanding idioms may pose problems.

There are two kinds of theories regarding how idioms are processed and understood. According to the Lexical Representation hypothesis, idioms are stored as lexical items, and understanding an idiom involves two parallel processes, a retrieval process (which is faster), and a literal compositional computation process based on decomposing every element separately (Swinney and Cutler, 1979).

Hamblin and Gibbs (1999) highlight idiom decomposability and suggest that idiom interpretation depends on identifying the individual constituents, because most idioms are decomposable. It is thus suggested that the processing and understanding idioms cannot be reduced to lexical access or lexical retrieval only (Cacciari and Tabossi, 1988; Gibbs, 1992; Vega-Moreno, 2001). This type of approach bridges over to the second type of approach, the configuration hypothesis. Authors that support it assume that idioms are represented in a distributed way and they are processed as complex expressions (Cacciari and Tabossi, 1988). Tabossi et al. (2005) found that spoken idiom identification differs from word recognition. This means that the modality of presenting the idiom may affect the way we process these expressions as well.

A central question in all of the above approaches to idiom processing, but also more broadly to figurative language processing, is whether literal meanings are accessed first, and whether at all. Some authors reject the existence of literal or default meanings altogether (Sperber and Wilson, 2006), while others suggest a revision of the concept of literal meaning (Ariel, 2002). Recent experimental research, however, provides evidence of the existence of literal meaning, and support for a possible distinction between basic/literal senses and interpretations, and extended/derived ones. Foraker and Murphy (2012) investigated how polysemous senses are processed during sentence comprehension. In this study, in a condition where the context was neutral and did not bias towards a specific sense, participants read disambiguating sentences faster when these sentences were compatible with the dominant sense of target words. Rubio Fernandez (2007) provides further evidence of the "lingering" presence of literal meaning in the processing of figurative language in the domain of metaphors, where core features of word meaning remained activated even after the metaphorical meaning was retrieved.

Idioms are easier to understand in the presence of supportive context. It has been commonly established that the main role of context is to provide semantic support for decoding the target (appropriate) meaning of a sentence or an expression (Cacciari and Levorato, 1989; Gibbs, 1991; Levorato and Cacciari, 1995; Vega-Moreno, 2001; Laval, 2003).

Several factors influence idiom comprehension. Idiomatic expressions can vary in transparency. It is much easier to understand more transparent expressions that opaque ones. Another factor is familiarity. It is a variable that influences comprehension, and many studies establish that a higher degree of familiarity increases performance, leading to better results in different comprehension tasks (Gibbs, 1991; Levorato and Cacciari, 1995; Nippold and Taylor, 2002; Lacroix et al., 2010).

We suggest here that competence in figurative language is characterized by the ability to process language beyond the literal interpretation of individual words. This competency relies both on inferencing skills and on the ability to integrate contextual information from both verbal and nonverbal sources. We expand this idea further in the next sections.

While much of extended language use goes unnoticed to typical native speakers of a language, and, as such may appear part of normal communication, it may pose severe problems for children and adults with developmental deficits. Such populations offer a glimpse into subtle dissociations between literal and nonliteral (figurative) language. For instance, in the autistic spectrum, even high-functioning individuals are often described as overly literal and often fail to appreciate figurative expressions. Such dissociations speak against the view that there exist no basic senses of lexical items (Sperber and Wilson, 2006), since these senses appear to be the only ones available to these individuals. This if often displayed in problems in the autistic spectrum with resolving linguistic ambiguity. We devote the rest of this paper to analyzing this issue and reviewing what data from individuals with autism can tell us about the true nature of figurative language.

### **FIGURATIVE LANGUAGE IN AUTISM SPECTRUM DISORDER**

Autism spectrum disorder (ASD) is a disorder characterized by impairments in social interaction and communication, and restricted behavior and interests. The impairment in social interaction can be manifested in marked deficiencies in the use of eye contact, reading facial expressions, emotions, body posture, and gestures. Failure to develop peer relationships, lack of spontaneous seeking to share enjoyment, interests, or achievements with other people and lack of social or emotional reciprocity, are also typical in autism.

Regarding the impairments in communication, the most common problem, even in individuals with adequate structural language, is the inability to initiate or sustain a conversation with others, including inability to maintain a topic shared with the interlocutor. In addition, ASD individuals frequently have a very stereotyped and repetitive use of language, thus leaving no room for spontaneity.

Individuals with ASD also show other restricted repetitive and stereotyped patterns of behavior, interests and activities. They may present encompassing preoccupation with one or more restricted patterns of interest. They are often characterized by lack of flexibility and adherence to specific, nonfunctional routines or rituals, repetitive motor mannerisms (e.g., hand or finger flapping or twisting, or complex whole-body movements). Often they display persistent preoccupation with parts of objects (e.g., wheels of a toy car).

### **POOR FIGURATIVE LANGUAGE IN ASD**

In typical language development, the acquisition of metalinguistic skills and the comprehension of figurative language seem to be achieved in childhood by the age of nine or ten years according to several authors. However, in ASD this process is typically delayed and depends on various factors, such as degree of language impairment, chronological age, context or social environment. Findings in research suggest that there is a delayed rate of development with regard to processing of ambiguity, idioms, metaphors and other types of figurative language in individuals with autism, and problems at more global levels of language structure, although performance may improve with age (Melogno et al., 2012a,b; Vulchanova et al., 2012a,b).

ASD is a disorder that significantly affects language and communication, and many individuals with ASD do not develop fluent language due to comorbidity with other impairments, such as intellectual disability or language disorder (LD). When LD is comorbid with autism, there are serious difficulties in understanding ambiguous linguistic information, as would be expected. In contrast, individuals with high-functioning autism are distinguished by relative preservation of linguistic and cognitive skills. They usually display a level of intelligence which is normal or even above average, and quite often have specific talents in certain areas. However, problems with pragmatic language skills have also been reported in their case, even with clear strengths in areas of grammar (Landa, 2000; Volden et al., 2009; Vulchanova et al., 2012a,b). Such dissociations in ASD between literal and figurative language argue against a simple continuity model.

One of the first studies to address figurative language comprehension and its roots in autism was the study by Happé (1995). It compared three groups of children with autism to a group of age- and VIQ-matched controls on the understanding of three types of expressions, synonyms, similes, and metaphors. In order to test the hypothesis that metaphor comprehension correlates with the ability to read minds and colocutors' intentions, participants were tested on both first-order, and second-order Theory-of-Mind (ToM) tasks. This study was inspired by ideas from Relevance Theory (Sperber and Wilson, 1986) and the aim was to put the basic assumptions of this account to the test, by investigating its predictions on the wellknown problems in aspects of pragmatic language in autism. The basic idea with the language stimuli used in the study, administered as a sentence completion task, was that there is a gradation of difficulty in processing language, ranging from full transparency in literal expressions to close to full transparency (similes), to nontransparency (metaphors). The findings from this study confirm that metaphor comprehension is impaired in children and adolescents with autism, against adequate processing of similes, and that the ability to process metaphors is directly linked to ToM ability. Thus, the ASD participants who passed both first- and second-order ToM tasks outperformed both participants who solved only the first-order tasks and those who did not pass either task.

The ToM account of the well-attested problems in autism with metaphor comprehension was tested further by Norbury (2005). In her study, an alternative hypothesis was put forth, namely that language competence is a better predictor of performance on metaphor tasks. For this purpose Norbury tested ASD children first grouped according to language ability and autistic symptomatology, and in a second analysis on their ToM ability. Both types of groups were compared to typically developing age-matched peers. The study included a number of tasks to establish language status: the British Picture Vocabulary scales (BPVS; Dunn et al., 1997), the Concepts and Directions subtest of CELF-III (Semel et al., 2000), and the Recalling sentences subtest of CELF-III. Semantic knowledge was tested on the Test of Word Knowledge (ToWK; Wiig and Secord, 1992), which includes synonyms, figurative language interpretation (idiomatic phrases), word definitions and word ambiguity (polysemy) testing. The results of this study demonstrate that semantic ability, which is a core language skill, is a better predictor of metaphor comprehension, whereas ToM, even though it predicts a proportion of the variance, is a weaker predictor of figurative language processing. Thus, only the children with a language impairment, with and without autism, showed impaired metaphor understanding. Furthermore, first-order ToM skills, while probably necessary, are not sufficient to ensure success with figurative language interpretation. These results, however, should be interpreted with caution, since the test used to assess semantic knowledge (ToWK) includes a number of subtests assessing figurative language comprehension, and as such, should, by definition, predict performance on metaphorical expressions (Rundblad and Annaz, 2010).

While the above two studies have only investigated metaphors, further research has targeted a broader range of figurative expressions. MacKay and Shaw (2004) report performance on six categories of expressions, including hyperbole, indirect requests, irony, metonymy, rhetorical questions and understatement. The assumption in their design is that all of these categories involve interpreting what is intended, rather than said, in each expression. For this purpose, the authors used two measures, correct understanding of the meaning of the expression, and correct understanding of the intent of the speaker. In this study language stimuli were accompanied by supporting picture material to provide visual focus for the participants. The experimental group included high-functioning ASD children compared to a control group with no communicative difficulties. In addition to the statistical analysis of results, the study also includes many examples of children's responses illustrating the specific pattern evident in the autistic spectrum in interpreting figurative expressions. This study documents a scale of difficulty in the area of figurative language, with irony standing out as (the most) challenging task, even for typical children, especially processing the intent of the speaker, and fewer problems in rhetorical questions, even for autistic children, where the meaning of such questions is accessible. Areas where a significant difference was observed between the typically developing children and the ASD group, include indirect requests (intent), understatements

(intent), as well as metonymy (both meaning and intent). The latter category was problematic even in the presence of visual support cues, and especially when the visual cues were less suggestive. Based on the finding that ASD children performed at the same level as the control group on understanding the meaning of certain figurative expressions (indirect requests, rhetorical questions, understatement), but failed at understanding the intent of those same expressions, the authors suggest that this result may be caused by different levels of language competencies and skills in the two groups, not evident in the results on the vocabulary scales (BPVS). Unfortunately, this study cannot be compared to the above two, since it did not address metaphors (but only metonymy), and did not ask the same question, namely the extent to which figurative language interpretation depends on ToM ability. Yet, it establishes a scale of difficulty in the processing of indirect language and compares performance by ASD children to typically developing peers in a range of figurative expressions.

Whyte et al. (2014) more recently studied idioms in children with ASD ages 5–12 years. They tested them on idiom comprehension, advanced ToM, vocabulary, and syntax. Like the other studies on figurative language, they also found that they performed worse than children matched on chronological-age. They were not, however, worse at understanding idioms than a syntax-matched control group of younger children. These results would support Norbury (2005) view that language impairment is actually the strongest factor in predicting performance on figurative language tasks.

Beyond group studies, a couple of case studies have addressed figurative language in autism. Melogno et al. (2012a) provide a case study of two high-functioning ASD children. Participants were assessed twice, first prior to, and subsequently following an intervention. Even though, initially the two ASD children showed performance comparable to the average range of typical controls, their patterns of response were different. Assessment after intervention revealed improvement, but in a different way for each participant. Moreover, the level of performance was still below their chronological age, indicative of a "drift" in figurative language comprehension.

In our own work we have addressed the cognitive and language profiles of two high-functioning (Asperger) children with a talent for language learning (Vulchanova et al., 2012a,b). These two case studies tested, among other language competencies, idiom comprehension and metaphor comprehension. Both participants in the studies displayed a highly deviant profile in idiom knowledge compared to similarly-aged controls. In the younger participant, the gap in performance with chronological age was huge (*z* = −3.08). Moreover, the participant performed poorer even than much younger children on the same task, suggesting a deviant developmental trajectory. Even though the gap with chronological age was somewhat smaller for the older participant (*z* = −2.22), it was still significant. The same participant showed an atypical pattern of responses to metaphorical expressions based on the design by Gold et al. (2010). In contrast to typical age-matched controls, for this participant, reaction times to novel metaphors and nonsense expressions were similar, reflecting a problem in distinguishing between these two types of expressions and assessing their plausibility.

Some studies have failed to find significant differences in accuracy scores for participants with autism in studies of figurative language comprehension. For example, Colich et al. (2012) tested whether children and adolescents with autism were able to interpret the ironic intent of speakers. Although both typically developing and autistic participants showed longer response times to ironic comments, brain activation profile was more bilateral in the case of the ASD group, indicating a potential compensation mechanism in processing this kind of figurative language. The study by Pexman et al. (2011) also found similar responses in an irony comprehension task, with results in eye-tracking variables and judgment latencies indicating that individuals with autism might be using different mechanisms to respond.

## **DEVELOPMENTAL ASPECTS OF FIGURATIVE LANGUAGE IN ASD**

In addition to the role of structural language abilities, a great deal of research has explored the influence of other variables that could potentially explain this deficit in the interpretation of nonliteral meaning in participants with autism. In this sense, an interesting question is whether these skills develop in relation to chronological age also in this population, and further whether there is development in relation to mental age. This was first studied from a developmental perspective by Rundblad and Annaz (2010). They compared performance on metonymy to metaphor performance in ASD and typical children. While metaphor is considered to represent a mapping between two distinct conceptual domains, metonymy is a mapping within the same conceptual domain (Lakoff, 1987), and, as such, may be considered a less demanding. The study included picture stories with lexicalized metaphors and lexicalized metonymies incorporated in brief stories. The authors established developmental trajectories for each group, and for each task, first assessing performance on the two tasks relative to chronological age. While for the typical group performance on both metonymy and metaphor increased reliably with chronological age, no reliable correlation was found between scores and chronological age on either task in the ASD children. In this group, in addition, children performed significantly worse on the metaphor task. These two tasks also revealed two different trajectories. While for metonymy there was a development, for metaphor, performance was constant across time and ages, indicating what the authors label a zero trajectory. Furthermore, this study shows that vocabulary scores predict reliably metonymy in the ASD group, with improved performance with higher verbal age, while no similar relationship was found for metaphor comprehension. Thus, compared to typical controls, the ASD group displays a similar rate of development for their level of receptive vocabulary in the area of metonymy, whereas the difference in metaphor comprehension is significantly different. This study adds an important developmental perspective, suggesting that metaphors are an area of specific difficulty where development is not only delayed (as with metonymy), but also highly atypical and, most likely, compromised.

Gold et al. (2010) studied metaphor comprehension in Asperger syndrome in adolescent and adult participants using four types of expressions, free (literal) expressions (*pearl necklace*), conventional metaphors (*sealed lips*), novel metaphors (*firm words*), and nonsensical expressions (*violin tiger*). Their main goal was to establish the accuracy of interpreting such expressions and the degree of cognitive load involved, as measured by reaction times and brain activation. The results of this study showed that compared to typical controls, Asperger individuals present with problems, as reflected in significantly longer reaction times compared to typical controls. Furthermore, different patterns of activation, as seen in the N400 amplitude, were found between the Asperger participants and the control group, which reached significance for the category conventional and novel metaphor. While, in the control group conventional metaphors elicited least negativity, for the Asperger group, it was literal expressions. This suggests greater effort in the processing of metaphor across the board in ASD individuals, including even conventional metaphors, which can be stored, as well as novel metaphorical expressions. Moreover, in the Asperger group reaction times were significantly longer for the processing of nonsense expressions. The latter result is indicative of a specific problem evident in other studies of figurative language in autism, namely the inability to assess the plausibility of linguistic expressions events or facts (Tager-Flusberg, 1981; Paul et al., 1988).

An interesting study provides evidence of a specific dissociation between the processing of visually presented metaphors and verbally presented ones in autistic populations (Mashal and Kasirer, 2012). This study compared ASD and Learning Deficit children to typically developing controls. They used 11 subtests, ranging from figurative language interpretation including visual metaphors, idioms, conventional metaphors, novel metaphors, to homophones and semantic tests (synonymy, similarity). The authors analysed the data using a Principal Component Analysis to investigate for clustering of performance results. Results loaded on three different factors in all three groups in the study, and while there was a significant overlap in the loading between groups, both deficit groups displayed a clustering of all three verbal figurative language skills (idioms, conventional and novel metaphors) in the same factor, suggestive of the specific problems in that population. Moreover, in those two groups there was a dissociation between metaphors presented visually, and those presented verbally, as reflected in the results loading on two different factors. In contrast, the typical children displayed an association between idioms and conventional metaphors, which can be expected, given the nature of conventionalized expressions and idioms, and an association between visual and novel metaphors, which loaded together on a separate factor. This latter result suggests an integration in typical individuals of the processing of metaphors, irrespective of their modality (visual or verbal), most probably through a common underlying cognitive mechanism. This does not appear to be the case in the autism group and the group with learning deficits.

All of the clinical studies reviewed here document a dissociation between literal and figurative language in autism, which argues against a simple continuity model. Clearly a revision of this model is called for in the face of these data.

### **ACCOUNTS OF THE PRAGMATIC DEFICIT: A SPECIFIC DEFICIT OR NOT?**

From the studies reviewed above and earlier findings, it becomes evident that there is a pervasive problem in the autistic spectrum in the broader domain of pragmatic aspects of language. However, there is a debate concerning the causes of this problem and what aspects of the autistic profile can account for the pragmatic deficit. One assumption is that the pragmatic deficit is not special and does not dissociate from the rest of language competence in autism. The idea is that performance on pragmatic tasks and the ability to process (ambiguous) language in context correlates directly with structural language competence (Norbury, 2005; Brock et al., 2008; Gernsbacher and Pripas-Kapit, 2012).

Alternatively, the pragmatic deficit can be linked to other traits in the autistic profile. Thus, one of the most widely accepted theories of what is causing the deficit in the domain of figurative language and metaphors, in particular, is based on Happé's study and hypothesis that the deficit is caused by impaired mentalising skills and in terms of impaired ToM (see also Baron-Cohen et al., 1985; Happé, 1993; Baron-Cohen, 2000, 2001). Clearly, the ToM hypothesis can explain one aspect of what is necessary to be able to perceive others' intentions, including those expressed verbally. Yet, many studies reveal increased problems with decrease in the transparency of the mapping between language structure and (intended) interpretation (MacKay and Shaw, 2004). All studies document a specific problem in the area of metaphors, even compared to closely related, but less demanding, phenomena, such as e.g., metonymy. This indicates that reading intentions (mentalising) needs to be operationalized accordingly on a finer scale of gradience, explaining difficulties and/or success in all types of figurative expressions.

A host of hypotheses attempts an account in terms of more general cognitive mechanisms dedicated to information processing. Some authors attribute the deficit to more general problems in executive functioning and the inability to suppress unnecessary information (Ozonoff et al., 1991; Mashal and Kasirer, 2012). This account links to the well-observed problem in assessing event plausibility (Tager-Flusberg, 1981), but also to the Weak Central Coherence account (Frith, 1989; Frith and Happé, 1994; Happé and Frith, 2006). Happé and Frith (2006) suggest that individuals with ASD have difficulties to understand metaphors, because they have a deficit in executive function and central coherence. This can be attributed to the fact that individuals with ASD display a bias for processing information locally rather than globally. Frith (1989) points out that in order to be able to understand a word or an expression they should be put in a concrete context. Context is even more important for figurative expressions, in order to process the intended meaning, rather than just the literal one. In fact, weak central coherence has been attributed as the source of pragmatic problems in individuals with ASD (Noens and van Berckelaer-Onnes, 2005). In addition, Norbury and Bishop (2002) found that people with ASD have difficulties in contextual integration, and the more ambiguous the expression is, the greater the problem in this population (Happé, 1997; Jolliffe and Baron-Cohen, 1999, 2000; López and Leekam, 2003; Brock et al., 2008).

Other accounts seek to explain the pragmatic deficit at the neural level in terms of a right hemisphere (RH) deficit (Gold and Faust, 2010; Gold et al., 2010). In one study, participants were asked to perform a semantic judgment task. The results indicated much less Right Hemispheric contribution to novel metaphor comprehension in ASD. Impaired RH activity was further documented in other studies of figurative language processing (Faust and Mashal, 2007).

Alternatively, it can be assumed that the inability to process figurative language arises from problems in information integration, especially when information is to be retrieved from multiple sources (e.g., problems with processing in context), and linking this to the more general deficit at global processing (top down) at the expense of enhanced local processing (bottom up). Of special interest here is that the well-documented problems in processing ambiguous information arise only in the context of language contra visual information (López and Leekam, 2003), and dissociates from structural language skills (Vulchanova et al., 2012a,b). Furthermore, there is evidence that visual and linguistic metaphors dissociate only in autistic participants, but not in typical children (Rundblad and Annaz, 2010). Therefore, it would be logical to conclude that the difficulties that people with autism demonstrate in figurative language are probably due to inability to either access both modalities at the same time or integrate information from more than one modality at the same time. While the visual context may assist interpretation in typical populations, it may create additional problems in deficit populations such as individuals with autism (Chahboun et al., in preparation).

Indeed, one of the main symptoms of ASD is the lack of information integration and absence of adaptability to the environment (Minshew et al., 1997; Brock et al., 2008). Many authors attribute this to the inability to gather together information in order to be able to distinguish between relevant and irrelevant information, in part attributable to weak central coherence (Frith, 1989; Happé and Frith, 2006; Vulchanova et al., 2012b). Selecting relevant features of the metaphor vehicle concept and suppressing the irrelevant ones has been suggested as the basic mechanism in metaphor comprehension (Rubio Fernandez, 2007).

It is widely argued that individuals with ASD are impaired in processing ambiguous linguistic information in context (López and Leekam, 2003; Brock et al., 2008). In addition, they often fail to attach context to their memories and are specifically impaired in processing social aspects of contextual information (Greimel et al., 2012).

Happé (1996) suggests that difficulties in global processing could be due to conceptual semantic deficits, but also to a failure in extracting perceptual properties from context. López and Leekam (2003) provide evidence that the ability to use context is spared in the visual domain, but reduced in the verbal one. Further, they document increased problems with increased complexity of the verbal stimuli and with higher level of ambiguity. This points to the limitations in the ability to use contextual information in individuals with ASD, but not a complete absence of this skill.

The extent to which individuals with autism can use context in disambiguation is an open question, and findings are controversial. Some authors consider that people with ASD are unable to use contextual information in sentence-processing tasks. Others still, claim that success or failure depend on the nature of the context: the more general the information provided by the context is, the more difficult it is for autistic participants to disambiguate homographs (Hermelin and O'Connor, 1967; Frith and Snowling, 1983; López and Leekam, 2003).

Saldaña and Frith (2007) and Tirado (2013) document that children with ASD have a normal reduction in reading times for expressions which are congruent with previous events, suggesting a relative strength at detecting congruence. It has also been argued that the ability to use context depends on structural language skills, and only ASD participants with poor language skills fail to use visual context (Norbury, 2005; Brock et al., 2008). What is clear from these studies is that different types of context present different processing demands, and autistic performance varies accordingly.

### **SUMMARY AND CONCLUSIONS**

Language is a complex multi-layered and multifaceted system. In order to interpret language appropriately, users need a number of skills. Figurative language can be even more demanding in terms of processing. It is acquired relatively late and has a complex nature, which makes it even more difficult for atypical population, such as individuals with ASD, to understand. What skills are deemed necessary for language processing and figurative language, in particular? Adequate structural language competence, adequate semantic competencies and skills and vocabulary size (Norbury, 2004, 2005; Oakhill and Cain, 2012), inferencing skills; a developed conceptual system and a knowledge base (Schneider et al., 1989; Fuchs et al., 2012; Oakhill and Cain, 2012); information integration skills (context; evaluating plausibility and suppressing irrelevant information, Rubio Fernandez, 2007); mentalising and understanding intentions (see Kintsch, 2000 for a computer simulation model). Needless to say, many of these skills co-vary with language (e.g., semantic skills and vocabulary, conceptual knowledge, and the knowledge base are often directly associated with linguistic labels), so studying them in isolation and controlling for their impact on figurative language depends on the kind of measure adopted. Impairment in any one of these areas is sufficient to cause problems in the comprehension of figurative language. For instance, in order to understand one of the most demanding instances of figurative language, metaphor, the user not only needs to have prior experience and knowledge of the concepts that are being associated in a metaphorical expression, but also knowledge of their respective domains and the networks they form with other concepts in these domains (Keil, 1986; Bambini et al., 2011). This requires information integration and processing skills, beyond those required for simple concept combination (Barsalou, 1999; Wu and Barsalou, 2009), and depends on the ability to form associations, analogies and

other top-down skills. If we take high-functioning autistic individuals as a test case, the cause of the persistent difficulty in figurative language becomes more evident. In this population, structural language is intact; they present with adequate semantic and conceptual skills, are good at compositional operations at the level of the sentence, perform adequately at a number of inferencing tasks (Tirado, 2013 PhD thesis), and usually pass first-order, and often second-order ToM tasks, and have an age-appropriate knowledge base, as attested by normal IQ scores. The only area where problems persist is information integration and inability to use information from the database adequately: evaluating plausible/implausible events; assessing what is relevant; combining information arising from different modalities.

Building on the original proposal by Kintsch (1998), an influential account of (reading) comprehension suggests that success at language processing depends on creating appropriate situation models. This means that the language user needs to create a mental representation of what the message is about, not what the message says (Zwaan, 1999). Based on the evidence in research on problems in the domain of figurative language interpretation, it is highly likely that autistic individuals have problems in building and making use of appropriate situation models. The models they build could in some respects be incomplete. More importantly, they might not be able to make use of them to understand the co-locutor's intention with the message. It seems as though, they possess the necessary knowledge base, but cannot use it adequately, since they cannot judge plausibility (Tager-Flusberg, 1981; Paul et al., 1988), often fail at certain types of inferences, and are not always good at exploiting contextual information. It has been shown that typical children benefit from visual support and are better at processing visually presented metaphors (Epstein and Gamlin, 1994). However, multi-modal and multi-sensory information appears to be a problem in autism, despite intact visual processing *per se* (López and Leekam, 2003; Chahboun et al., in preparation). As a consequence, individuals in the autistic spectrum fail to integrate a situation model that integrates the necessary information, the speaker's intent and the rest of the context in which all this must be used.

### **DIRECTIONS FOR FUTURE RESEARCH**

Most of the studies reviewed in this paper are heterogeneous and difficult to compare. They have used different methodologies, test skills in different figurative language domains, and often use largely heterogeneous groups of participants. Thus, quite often the range of participants is from mid-childhood to adulthood. Since one of the intriguing questions in research in developmental deficits is whether one can expect development in the comprehension of the different types of figurative expressions, more homogenous groups are required, in both longitudinal and cross-sectional studies (cf. Melogno et al., 2012b for a similar point). Similarly, the types of expressions selected in those studies vary tremendously, especially those that have been chosen as exponents of the target category. For instance, the degree to which expressions fall in the category of conventional metaphor needs to be tested prior to including it in an experiment. Likewise, other linguistic properties of the stimuli are important: frequency of expression and/or constituent words will affect processing; collocational frequency of the constituents in the expression (e.g., "buckle" and "button" are by far the most frequent complement fillers of "fasten", as in fasten a buckle/a belt, so these phrases tells us little about argument structure competence in typical and deficit populations alike).

The observed dissociation between figurative (non-literal) and literal language processing in ASD lends support to findings about the neural correlates of idiomatic language processing in typical adult populations (Lauro et al., 2008), suggesting a bilateral involvement of fronto-temporal areas for idioms against selective activation of left inferior parietal areas in the case of literal expressions. The recruitment of the prefrontal cortex may reflect an active selection between alternative meanings when idioms are processed. This offers a new perspective for future research comparing the neural and cognitive mechanisms involved in figurative language comprehension in autism and typical populations.

Another intriguing line of research are recent accounts of the role of embodiment in human cognition and, specifically, in language comprehension (Barsalou, 2008). It has been suggested that the well-attested communication problems in autism could be partially driven by core (low-level) cognitive mechanisms, such as deficits in temporal coordination and sensori-motor impairment (e.g., motor movement). This type of account is consistent with models of embodied cognition in typical populations and is worth pursuing in future research (Eigsti, 2013).

An interesting, yet unexplored perspective are parallel studies of similar pragmatic deficits observed in different developmental disorders. For instance, Lacroix et al. (2010) document problems in idiom comprehension in French speaking children and adolescents with William's syndrome. Similar results have been found while testing the ability to understand metaphors and sarcasm (Karmiloff-Smith et al., 1995; Annaz et al., 2009). Since WS is characterized by a relative strength in language and social interest, but poor conversational skills, contra impaired spatial cognition, it would be interesting to test how this population compares to the autistic spectrum, especially the higher end, where structural language is spared, too. Even more intriguingly, it has been suggested that the observed figurative language problems in WS may be attributed to poor semantic integration (Hsu, 2013).

Finally, if we are right in attributing the figurative language deficit to poor information integration and impaired situation models, appropriate tasks need to be set up to test for exactly these types of skills. Developmental deficits offer a rare glimpse into the, sometimes subtle, dissociations between and within cognitive domains, such as e.g., structural vs. extended (figurative) language, and as such, can shed light on how metaphors and other figurative expressions are processed in typical individuals, what kinds of demands this processing requires and at what cost. Future research should seek to provide a consistent comprehensive account of the mechanisms involved in language comprehension at the neural and cognitive levels in both typical and deficit populations (Dilkina and Lambon Ralph, 2013).

# **ACKNOWLEDGMENTS**

This work has been supported by the EU 7th Framework Programme Marie Curie Initial Training Networks grant Nr. 316748 under the project *Language and Perception* and Grant PSI2010-17401 of the Spanish Ministry of Science and Innovation to the second author.

# **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.

### *Received: 14 April 2014; accepted: 11 January 2015; published online: 17 February 2015*.

*Citation: Vulchanova M, Saldaña D, Chahboun S and Vulchanov V (2015) Figurative language processing in atypical populations: the ASD perspective. Front. Hum. Neurosci. 9:24. doi: 10.3389/fnhum.2015.00024*

*This article was submitted to the journal Frontiers in Human Neuroscience*.

*Copyright © 2015 Vulchanova, Saldaña, Chahboun and Vulchanov. This is an openaccess article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution and 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*.

# Flying under the radar: figurative language impairments in focal lesion patients

## *Geena R. Ianni 1 †, Eileen R. Cardillo2 \*†, Marguerite McQuire2 and Anjan Chatterjee2*

1 Section on Neurocircuitry, Laboratory of Brain and Cognition, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA 2 Department of Neurology, Center for Cognitive Neuroscience, University of Pennsylvania, Philadelphia, PA, USA

### *Edited by:*

John J. Foxe, Albert Einstein College of Medicine, USA

### *Reviewed by:*

Krishnankutty Sathian, Emory University, USA Christelle Declercq, Université de Reims Champagne-Ardenne, France

### *\*Correspondence:*

Eileen R. Cardillo, Department of Neurology, Center for Cognitive Neuroscience, University of Pennsylvania, 3720 Walnut Street B-51, Philadelphia, PA 19104-6241, USA

e-mail<EMAIL_ADDRESS>
†Geena R. Ianni and Eileen R. Cardillo have contributed equally to this work.

Despite the prevalent and natural use of metaphor in everyday language, the neural basis of this powerful communication device remains poorly understood. Early studies of brain-injured patients suggested the right hemisphere plays a critical role in metaphor comprehension, but more recent patient and neuroimaging studies do not consistently support this hypothesis. One explanation for this discrepancy is the challenge in designing optimal tasks for brain-injured populations. As traditional aphasia assessments do not assess figurative language comprehension, we designed a new metaphor comprehension task to consider whether impaired metaphor processing is missed by standard clinical assessments. Stimuli consisted of 60 pairs of moderately familiar metaphors and closely matched literal sentences. Sentences were presented visually in a randomized order, followed by four adjective-noun answer choices (target + three foil types). Participants were instructed to select the phrase that best matched the meaning of the sentence. We report the performance of three focal lesion patients and a group of 12 healthy, older controls. Controls performed near ceiling in both conditions, with slightly more accurate performance on literal than metaphoric sentences. While the Western Aphasia Battery (Kertesz, 1982) and the objects and actions naming battery (Druks and Masterson, 2000) indicated minimal to no language difficulty, our metaphor comprehension task indicated three different profiles of metaphor comprehension impairment in the patients' performance. Single case statistics revealed comparable impairment on metaphoric and literal sentences, disproportionately greater impairment on metaphors than literal sentences, and selective impairment on metaphors. We conclude our task reveals that patients can have selective metaphor comprehension deficits. These deficits are not captured by traditional neuropsychological language assessments, suggesting overlooked communication difficulties.

**Keywords: metaphor, aphasia, focal lesion patients, figurative language, case study, sentence comprehension**

# **INTRODUCTION**

Metaphor is pervasive in everyday language, and often used to communicate complex, abstract, or unfamiliar concepts. Individuals encounter metaphors on a daily basis in the classroom *(The Bohr model atom is a tiny solar system*), in their social lives*(Our first date was a train wreck*), and in the media *(Congress froze the budget*). As a communication device, metaphor is practical, allowing familiar information to sculpt and inform new concepts. Conceptualized this way, metaphor is fundamental to the flexibility of human thought, revealing novel commonalities, facilitating learning, and enabling abstraction (Lakoff and Johnson, 1980; Gentner, 1983).

Despite the ubiquity of metaphor in thought and language, its neural instantiation remains uncertain. In an early formal demonstration of metaphor deficits following brain injury, Winner and Gardner (1977) found that right-hemisphere damaged (RHD) patients, but not left-hemisphere damaged (LHD) patients or healthy controls, had difficulty matching metaphoric sentences to pictures, suggesting the right hemisphere was uniquely tuned for metaphor comprehension.

Several subsequent patient studies supported this claim (Brownell et al., 1984, 1990; Van Lancker and Kempler, 1987; Mackenzie et al., 1999; Champagne et al., 2004; Klepousniotou and Baum, 2005a,b). However, in some of these cases only RHD patients and controls were tested, providing no means of comparison between the hemispheres (Mackenzie et al., 1999; Champagne et al., 2004, 2007; Rinaldi et al., 2004) or RHD patients who performed at ceiling were excluded from analyses (Brownell et al., 1990). These studies sometimes also contained few items (e.g., as few as three or four in Brownell et al., 1990; Tompkins, 1990; Giora et al., 2000; Zaidel et al., 2002), showed that impairment depended on task (Winner and Gardner, 1977), or failed to show any hemispheric differences when task demands were accounted for statistically (Zaidel et al., 2002). Nonetheless, the first neuroimaging study of metaphor comprehension supported the right-hemisphere hypothesis (Bottini et al., 1994), bolstering the tentative claims made by the patient studies. Thus, the prevailing view became that metaphor comprehension was a lateralized, right hemisphere dominant process.

Many subsequent neuroimaging studies of metaphor comprehension, however, have failed to find the right-lateralized activations predicted by the right-hemisphere hypothesis of metaphor comprehension.  Recent meta-analyses confirm left-hemisphere dominance for figurative language, including metaphor. Although the right hemisphere is indeed often responsive to metaphoric stimuli, its contribution is neither equivalent to nor stronger than that of the left hemisphere; it is weaker (Rapp et al., 2012) or absent (Bohrn et al., 2012). Consistent with this conclusion, some patient studies found metaphor comprehension to be comparably impaired following left or right hemisphere injury (Tompkins, 1990; Gagnon et al., 2003), or more impaired following left than right injury (Giora et al., 2000).

Unsurprisingly, divergent lesion and neuroimaging data have not led to consensus regarding the laterality of metaphor comprehension (Schmidt et al., 2010). One explanation for these discrepancies is heterogeneity of stimuli and/or task demands. We have addressed stimulus design extensively elsewhere (Cardillo et al., 2010) and will address choice of task here. Tasks common in neuroimaging studies with healthy adults do not always extend well to patient populations. On the one hand, passive tasks like silent reading or periodic comprehension probes provide insufficient behavioral correlates for measurement. On the other hand, more demanding, semantic tasks like valence or plausibility judgment may elicit poor performance because of difficulty with the decision aspect of the task or a response-bias, not because of a comprehension problem, *per se*. These tasks also cannot tell us anything about what a person understood the sentence to mean. Comprehension of metaphoric sentences could be assessed with yes/no questions (Gagnon et al., 2003; Eviatar and Just, 2006; Prat et al., 2012), however, this task produces a relatively insensitive measure. Random guessing alone would produce 50% accuracy. Further, poor performance can only indicate a patient has metaphor comprehension difficulty, but provides no insight into the many possible reasons for a comprehension failure.

Experimental tasks commonly used with patients also present interpretive challenges. Evaluating metaphor comprehension with picture-matching may introduce visuospatial confounds in RHD patients, who perform better than LHD patients when asked to provide oral explanations of the same metaphors (Winner and Gardner, 1977; Mackenzie et al., 1999; Giora et al., 2000; Zaidel et al., 2002; Rinaldi et al., 2004). Oral explanations provide rich information but are difficult to quantify and necessitate fewer items than forced choice tasks (Giora et al., 2000; Zaidel et al., 2002; Champagne et al., 2004). In addition, some LHD aphasics may have difficulty conveying full comprehension in this format because of language production problems (Winner and Gardner, 1977). Semantic similarity judgments – in which a patient matches a metaphoric expression (e.g., *bright*) to

its figurative sense (e.g., *clever*) – avoid many of the previously mentioned confounds. However, stimuli used in such tasks have been highly heterogeneous. Single words, dyads, and triads have all been used and studies have varied in how thoroughly or comparably they have matched answer choices and conditions on lexical confounds that are not of interest (Brownell et al., 1984, 1990; Gagnon et al., 2003).

Clinical assessments of language function following brain injury are even less discerning. Neurologists, speech pathologists, and neuropsychologists rely on diagnostic batteries to reveal compromised language skills, target speech-language rehabilitation approaches, and alert patients and their caregivers to areas of potential communication difficulty. The commonly administered Western Aphasia Battery (WAB; Kertesz, 1982), for instance, assesses spoken and written language production and comprehension, classifying patients by aphasia diagnosis and severity of impairment in different domains.

Although widely used, the WAB exclusively assesses literal language skills. Other aphasia assessments are similarly lacking. The Boston Diagnostic Aphasia Examination (Goodglass and Kaplan, 1983), the Porch Index of Communicative Ability (Porch, 1971), Minnesota Test for Differential Diagnosis of Aphasia (Schuell, 1965), and the Aphasia Diagnostic Profiles (Helm-Estabrooks, 1992) also do not contain any assessment or mention of metaphor. This clinical oversight runs contrary to common experience. Other batteries such as the Right Hemisphere Language Battery (Bryan, 1989) and Montreal Evaluation of Communications (Joanette et al., 2004) do include a figurative subtest but rely on items not motivated by current theoretical and methodological considerations relevant to metaphor comprehension (Cardillo et al., 2010; Schmidt et al., 2010). Furthermore, these batteries are rarely administered to patients with left hemisphere injury.

Given the limitations of existing metaphor comprehension tasks, we developed a new sentence-level, multiple-choice matching task to address these methodological challenges. Sentence stimuli – a staple of neuroimaging studies of metaphor – are preferable to single words, as they are metaphor's most commonly encountered form. Their complexity however, requires careful balancing between figurative and literal conditions in terms of difficulty, a level of control that is rarely documented. Despite their naturalness and the feasibility of generating closely matched stimuli (e.g., Cardillo et al., 2010), sentence-level metaphors have not to our knowledge been used with patients. In our task, participants read a sentence and then chose from an array of four phrases the one that best matches its meaning (one correct target, three incorrect foils). This task has several advantages over other measures: (1) it avoids the visuospatial confounds of picture-matching, (2) it avoids the qualitative nature of oral explanations, (3) it avoids the low sensitivity of yes/no questions, (4) it uses naturalistic language, and (5) it explicitly acknowledges different metaphor subtypes. We demonstrate that the metaphor multiple choice task can be used to reveal unrecognized metaphor deficits in braininjured patients by presenting three illustrative cases. We further demonstrate that this approach can identify metaphor-specific deficits, distinct from general comprehension deficits and unrecognized by traditional neuropsychological assessments of language. Finally, we show that systematically designed foils provide

information about the nature of a patient's comprehension failure.

### **MATERIALS AND METHODS**

### **SUBJECTS**

Participants were three unilateral focal lesion patients enrolled in the University of Pennsylvania Focal Lesion Database. Patients with a history of other neurological disorders, psychiatric disorders, or substance abuse are excluded from the database. The patients presented here were drawn from an ongoing, large-scale group study of metaphor comprehension and specifically selected based on their observed behavioral patterns on our task. Sample size was dictated by the number of unique comprehension profiles that, when presented together, illustrate the capability of our task to detect and distinguish different kinds of metaphor impairment. Detailed demographic and neuropsychological information about the patients is provided in **Table 1** and an axial view of their injury location is provided in **Figure 1**.

Patient 444DX is an 81 year-old retired factory worker who suffered an ischemic stroke 120 months prior to testing. The Philadelphia Brief Assessment of Cognition (PBAC), a brief dementia-screening instrument, was administered to assess function in five cognitive domains: working memory/executive control, lexical retrieval/language, visuospatial/visuoconstructional operations, verbal/visual episodic memory, and behavior/social comportment (Libon et al., 2011). Performance indicated compromised visuospatial, memory, and executive functions but normal language and social skills. Object and action naming battery (OANB) scores confirmed clinically normal lexical access for common object and action names (Druks and Masterson, 2000) and administration of the Western Aphasia Battery (Kertesz, 1982) likewise indicated clinically normal language abilities. An MRI scan demonstrated a lesion damaging the posterior temporal and parietal cortex of the right hemisphere.

Patient 384BX is a 74 year-old, retired butcher who suffered a hemorrhagic stroke 144 months prior to testing. Performance on the PBAC indicated compromised visuospatial, memory, and executive functions but normal language and social skills. Following injury he reported halting speech and stuttering. Administration of the WAB revealed some residual difficulty with naming and a

diagnosis of mild anomia. OANB scores, however, indicated clinically normal lexical access for common object and action names. An MRI scan demonstrated a lesion undercutting the superior frontal gyrus of the left hemisphere.

Patient 642KM is a 78 year-old retired construction manager who suffered an ischemic stroke 130 months prior to testing. Performance on the PBAC indicated compromised memory and executive function but normal visuospatial, language, and social skills. OANB scores indicated clinically normal lexical access for common object and action names, and the WAB score indicated clinically normal language abilities. An MRI scan demonstrated a lesion damaging the parietal cortex of the left hemisphere.

Twelve neurologically healthy older adults recruited from the University of Pennsylvania Control Database served as a control population (Age: 64.3 ± 9.9, Education: 14.4 ± 2.6) and were paid \$15/h for their participation. All participants were native English speakers, right-handed and gave informed consent to participate in accordance with the Institutional Review Board of the University of Pennsylvania.

### **STIMULI**

### *Sentences*

Stimuli consisted of 60 metaphor-literal sentence pairs of three types. One third of the items were of the nominal-entity form, one third were of the nominal-event form, and one third were of predicate form. Nouns referring to concrete entities or objects (e.g., *bullet*, *cheetah, drum*) served as the metaphorical words in nominal-entity sentences, nominalized verbs in nominal-event sentences [e.g., *(a) dance, (a) limp, (a) fall*], and verbs in predicate sentences (e.g., *ran, giggled, argued*). All nominal-entity and nominal-event metaphors were of the form "*The X was a Y*" where *Y* was the word being used metaphorically. All predicate metaphors consisted of a noun phrase and an action verb followed by a prepositional phrase. In these items the verb was the word used metaphorically. It remains to be seen if different types of metaphor are also delineated at the cognitive or neural level (Cardillo et al., 2012). Given that objects and actions, as well as nouns and verbs, have been shown to differ in their semantic properties and neural instantiations (Damasio and Tranel, 1993; Martin et al., 1995; Kable et al., 2002, 2005) it is possible that their

T, temporal; P, parietal; F, frontal; Exec, executive function; Mem, Verbal/visual episodic memory; VisSp, visuospatial/visuoconstructional operations; Lang, lexical retrieval/language; Beh, behavior/social comportment.

1Voxel size = 1 mm × 1 mm × 1 mm; 2Within normal limits cut-off = 93.8.

figurative extensions do as well. Although investigating the role of syntactic form and semantic properties of source terms was not the focus of this study, the possibility of encountering categoryspecific deficits dictated that different types of metaphor were balanced.

Forty nominal-entity, 40 nominal-event, and 40 predicate sentence pairs were selected from a superset of 624 sentence pairs [80 pairs were taken from Cardillo et al. (2010) and 80 pairs were drawn from a pool of 312 items designed and normed using identical methods] using Stochastic Optimization of Stimuli software (Armstrong et al., 2012). Optimized selection ensured metaphors and literals were matched in terms of familiarity, length (number of words, number of content words, number of characters), average content word frequency, average content word concreteness, and positive valence ratio (*p*'s > 0.10). As previously observed

**Table 2 | Psycholinguistic properties of literal and metaphoric sentences.**

(Cardillo et al., 2010), metaphors were judged to be significantly less imageable (*p* < 0.005) and natural (*p* < 0.01) than their literal counterparts, and significantly more figurative (*p* < 0.005). Sentences of different types (nominal-entity, nominal-event, predicate) were further matched on interpretability (metaphors only), figurativeness (metaphors only), familiarity, naturalness, imageability, length (number of words, number of content words, number of characters), frequency, concreteness, and positive valence ratio (*p*'s > 0.10). Means and standard deviations of 12 collected psycholinguistic variables are summarized below in **Table 2**.

### *Answer choices*

Four answer choices were generated to accompany each sentence: one correct target and three incorrect foils. All answer choices were composed of an adjective or adverb, followed by a noun. As shown in **Table 3**, in the metaphor condition the target was related to the figurative meaning of the sentence, Foil 1 was related to the literal sense of the sentence, Foil 2 was the opposite of the metaphorical sense of the sentence, and Foil 3 was unrelated. Foils were designed to be informative of the type of language deficit present. A Foil 1 selection indicates a literal bias in metaphor comprehension. A Foil 2 selection indicates a semantic integration impairment, as the metaphorical sense of the source word was necessarily activated but incorrectly interpreted in the context of the sentence. A Foil 3 selection indicates a more general comprehension deficit, as it is entirely unrelated to the sentence.

In the literal condition, the foils were designed to mirror the difficulty and nature of foil types in the metaphor condition as closely as possible. The target was related to the literal meaning

\*SUBTLWF values from Brysbaert and New (2009).

#### **Table 3 | Sentence and answer choice examples.**

of the sentence, Foil 1 was related to the agent of the sentence by category membership (but not implied by the sentence), Foil 2 was the opposite of the literal sense of the sentence, and Foil 3 was unrelated. It was necessarily impossible to make Foil 1 answers of the same nature as Foil 1 answers in the metaphor condition, but by presenting a strong lexical associate of one of the content words, Foil 1 answers were designed to mirror the semantic selection demands of Foil 1 answers in the metaphor condition (which presented a meaning strongly associated with the source term). Given the reversed valence necessarily entailed by the Foil 2 condition (the opposite of the target meaning), an additional constraint on all answer choices was introduced to avoid valencerelated biases in selection: for both metaphor and literal items, Target and Foil 2 had opposite valences and Target and Foil 3 had the same valence.

Finally, frequency values for the answer choices were collected from SUBTLEXus (Brysbaert and New, 2009). No significant differences in average frequency were found between literal and metaphor conditions, between sentence types, or between answer choices. Concreteness values were also collected from the MRC Psycholinguistic Database (Coltheart, 1981) and the University of South Florida Norms (Nelson et al., 2004). For those words that did not have published concreteness values, we collected our own using the procedures of Cardillo et al. (2010). Given the abstract nature of metaphor, Target and Foil 1 answer choices were significantly different in terms of average concreteness (*p* < 0.005). In order to avoid any concreteness-related bias in selection, an additional constraint on all answer choices was introduced: Target and Foil 3 also significantly differed in concreteness (*p* < 0.005) and the target and Foil 2 did not (*p* > 0.10). Literal answer choices also followed this pattern: Target and Foil 1 differed in concreteness (*p* < 0.001), as did Target and Foil 3 (*p* < 0.005), but Target and Foil 2 did not (*p* > 0.10). As such, answer choices were matched on frequency, concreteness and valence so none could aid blind guessing. **Table 3** provides examples of sentence and answer choice stimuli. Full materials are available upon request.

### **PROCEDURE**

### *Control procedure*

All participants made judgments on all 120 items. Subjects were told to choose the single answer choice which best matched the "meaning of the sentence," and to guess if unsure. The task was selfpaced. Participants pushed the space bar once for the sentence to appear. After reading the sentence for comprehension, participants pushed the space bar again to view the answer choices. Answer

choices were presented in quadrant format below the sentence, Participants were instructed to indicate an answer choice using four keys on the keyboard. Sentences were presented centrally in black, 18-point font on a white background using E-Prime 1.1 software on a Dell Inspiron laptop. Each participant received a unique, random order of items. The target and each foil had a 25% chance of appearing in any single quadrant on the screen in any given trial. Ten practice trials preceded four blocks of experimental trials.

### *Patient procedure*

The patients' task was similar to the controls' with one modification: the trials were advanced by the experimenter. The experimenter pressed the spacebar for the sentence to appear. This was followed by a 3 s delay, and then the answer choices were presented beneath the sentence. To avoid motor response and memory difficulties, patients indicated an answer by pointing to or saying the answer aloud and the experimenter recorded this answer using the keyboard.

### **BEHAVIORAL ANALYSIS**

An item analysis of healthy controls' scores revealed three items whose comprehension fell 3 SD below the average; these items were eliminated from further analysis. A subject analysis of accuracy scores revealed a single individual whose comprehension fell 3 SD below average on any given sentence-type; this individual was replaced. For controls, accuracy for literal and metaphor conditions was averaged across all participants. For patients, accuracy in the literal and metaphor conditions was calculated separately for each individual. Foil profiles were generated for each patient by dividing the number of each type of error (Foil 1, Foil 2, Foil 3) by the total number of errors in literal and metaphor conditions.

We tested for a comprehension deficit in the metaphor condition at the level of the individual patient using "Bayesian analysis for a *simple* difference," developed by Crawford et al. (2010). The analysis was done on standardized scores and repeated for the literal condition. This test uses Bayesian Monte Carlo methods to determine if a patient's score is sufficiently below the scores of controls such that the null hypothesis, that the patient's score is an observation from the control population, can be rejected. In this case, patients with a *simple* metaphor or literal deficit exhibit significantly reduced comprehension in that condition, relative to controls.

We also tested for a differential deficit in metaphor comprehension at the level of the individual patient using "Bayesian analysis for a *differential* difference," developed by Crawford et al. (2010). The Bayesian test for a *simple* difference can only indicate whether a patient is impaired in the metaphor, literal, or both conditions. It does not distinguish between reduced accuracy due to difficulty with metaphor specifically and reduced accuracy due to a general impairment affecting literal and metaphoric language alike. The Bayesian test for a *differential* difference however, can make this distinction by also taking into account the differential accuracy score and correlation between the two conditions, as established by the control group. Patients with a *differential* metaphor deficit exhibit proportionally greater difficulty with metaphoric than literal sentences than is observed in the control population.

# **RESULTS**

Overall, the control group performed near ceiling. Literal accuracy (*M* = 96.8, SD = 1.98) was significantly higher than metaphor accuracy (*M* = 93.5, SD = 4.65); *t*(11) = 2.744; *p* = 0.019). The correlation between literal and metaphor accuracy was *R* = 0.516 (*p* = 0.044). In the metaphor condition, Foil 1 (the literal sense of the sentence), was the most common error (66.7%), followed by Foil 2 (24.4%) and Foil 3 (8.9%). In the literal condition, Foil 1 (related to the agent of the sentence by category membership, but not implied by the sentence), was the most common error (78.3%), followed by Foil 2 (17.4%) and Foil 3 (4.3%).

### **GENERAL SENTENCE COMPREHENSION IMPAIRMENT (444DX)**

Application of the Bayesian test for a simple deficit revealed a simple metaphor comprehension deficit [*t*(11) = −3.653; *p* < 0.01] and a simple literal comprehension deficit [*t*(11) = −5.004; *p* < 0.001], in 444DX. Application of the Bayesian test for a differential deficit revealed a non-significant difference in metaphor and literal comprehension scores, indicating a general sentence comprehension impairment. 444DX made predominantly Foil 1 and Foil 2 errors in both the metaphor and literal conditions. See **Table 4** for detailed reporting of single case statistics.

### **DISPROPORTIONATE IMPAIRMENT IN METAPHOR COMPREHENSION (384BX)**

Application of the Bayesian test for a simple deficit revealed a simple metaphor comprehension deficit [*t*(11) = −8.640; *p* < 0.005] and a simple literal comprehension deficit [*t*(11) = −4.182; *p* <0.001] in 384BX. Application of the Bayesian test for a differential deficit revealed a differential metaphor deficit [*t*(11) = 4.656; *p* < 0.02]. In the metaphor condition, 384BX's errors were overwhelmingly Foil 1, while Foil 2 accounted for the majority of errors in the literal condition. See **Table 5** for detailed reporting of single case statistics.

### **SELECTIVE IMPAIRMENT IN METAPHOR COMPREHENSION (642KM)**

Application of the Bayesian test for a simple deficit revealed a simple metaphor comprehension deficit [*t*(11) = −5.790; *p* < 0.0001] in 642KM. Literal comprehension was not significantly different than that of controls. Application of the Bayesian test for a differential deficit revealed a differential metaphor deficit [*t*(11) = 5.129; *p* < 0.001]. Like 444DX, 642KM made predominantly Foil 1 and Foil 2 errors in both the metaphor and

literal conditions. See **Table 6** for detailed reporting of single case statistics.

To summarize, the three patients exhibited three distinct deficit patterns. 444DX demonstrated general sentence level impairment; she was impaired on both metaphor and literal comprehension, but not significantly more so on either condition. 384BX demonstrated a disproportionate metaphor deficit; he was impaired on both metaphor and literal comprehension, but significantly more so for metaphors. 642KM demonstrated a selective metaphor deficit; he was impaired on metaphors but displayed normal literal comprehension.

# **DISCUSSION**

Metaphors are powerful and pervasive communication devices in everyday language, yet conspicuously absentfrom standard clinical assessments of language. The purpose of this study was to demonstrate that a metaphor multiple-choice task can reveal profiles of impaired metaphor comprehension in brain-injured patients that go undetected by traditional aphasia assessments. Three unilateral focal lesion patients made judgments on 60 matched literal-metaphor sentence pairs by choosing the phrase that best matched the meaning of a given sentence from an array of four possible answers. Compared to a group of healthy, older adults, single-case statistics revealed three unique patterns of impaired metaphor comprehension in the three patients (444DX, 384BX, 642KM). None of these patterns were predicted by their performance on standard clinical measures of receptive and expressive language.

Although the WAB is widely used to diagnose and classify aphasia following brain injury, it is agnostic with respect to figurative language, including metaphor. Our data indicate profound, unrecognized deficits in this domain, impairments that can persist post-injury despite normal literal language comprehension, and may significantly impact daily communication and thinking. All three cases in our series were impaired in their comprehension of metaphoric sentences, but the specific pattern of performance suggests these deficits were of three different natures.

444DX was impaired in both literal and metaphoric conditions. The absence of a differential deficit suggests that her difficulty with metaphor reflects a general sentence comprehension impairment. 444DX's low performance is surprising considering her near perfect accuracy on the WAB, OANB, the language subsection of the PBAC, and casual conversation. One possibility is that her behavior reflects, at least in part, difficulty with the semantic executive demands of the task. A multiple choice problem requires the systematic consideration and rejection of competing meanings before selecting the correct one. 444DX's performance on the PBAC indicated impaired memory and executive function, domain general deficits would reasonably impact strategic processing in the linguistic domain as well. Consistent with a difficulty in resolving semantic competition, 444DX remarked, "Some of them were tricky. A lot of times, I thought there were two correct answers. I doubted myself several times."

384BX was also significantly impaired in both his literal and metaphoric comprehension, responding correctly to only 88% of the literal sentences, and only 52% of the metaphoric sentences. Unlike 444DX, however, the difference between his metaphoric

and literal comprehension was greater than would be expected in healthy adults, indicating a disproportionate difficulty with metaphor. This pattern suggests that a milder, lexical-semantic comprehension impairment is present in addition to a metaphorspecific deficit. The severity of 384BX's diagnosed anomia, however, is mild and not suggestive of the severe metaphor impairment observed. Furthermore, anomia is classified as an expressive aphasia, in which language production is affected while comprehension is relatively preserved. Therefore 384BX's poor metaphor comprehension cannot be anticipated by the anomia diagnosis. Nor is he aware of his difficulty. In debriefing he remarked, "I started stuttering after the stroke," but "I can still read and remember," and "I did not feel like my reading was affected (by the injury)."

Most dramatic was the disproportionate metaphor deficit demonstrated by 642KM. Consistent with his high scores on the neuropsychological tests and conversational ease, his performance in the literal condition was near ceiling – yet he responded correctly to only 66% of metaphoric sentences. This pattern indicates his comprehension failure is specific to metaphor and cannot be explained by general language comprehension problems. Like 384BX, 642KM remained unaware of his impairment even after testing, remarking, "it was easy," and "I understood ninety percent of what I was reading." As these comments suggest, this comprehension problem is not only unrecognized by traditional aphasia assessments, but is also opaque to the patient himself.

As the three cases illustrate, not all metaphor deficits are alike. Some deficits are "pure," selective for metaphor while leaving literal language intact (642KM). In other patients this metaphorspecific deficit is accompanied by a milder comprehension deficit affecting literal language as well (384BX). Still other metaphordeficits are reflective of a general deficit, impacting metaphoric and literal language comprehension similarly (444DX). The close matching of metaphoric and literal conditions on psycholinguistic variables enables confident direct comparison of metaphor and literal comprehension. By contrast, many previous studies have tested patients on only metaphoric items (Winner and Gardner, 1977; Mackenzie et al., 1999; Giora et al., 2000; Zaidel et al., 2002; Champagne et al., 2004; Rinaldi et al., 2004), designs that cannot preclude the possibility of a general comprehension deficit, rather than a metaphor-specific one.

The unique foil profiles of each patient further illustrate the diversity of metaphor deficits. 384BX's errors in the metaphor condition were overwhelmingly Foil 1 (literal interpretation). This pattern indicates his metaphor comprehension fails in a specific way, resulting in a systematic, highly implausible misinterpretation. Literal biases have been reported previously in brain-damaged patients by Brownell et al. (1984) and Rinaldi et al. (2004), using picture-matching and a single-word semantic similarity judgment task, respectively. The present study is the first demonstration of literal bias for metaphor comprehension in which metaphor and literal items were closely matched on average and in pairwise fashion. Thus, we may confidently attribute comprehension deficits to difficulty with metaphors, rather than potentially confounding sentence properties (e.g., familiarity, length, frequency, concreteness, etc.). In contrast to 384BX, 642KM, and 444DX showed more mixed foil profiles,

**Table 4 | Single case statistics and foil profile of 444DX.**

with Foil 2 errors in addition to Foil 1 errors. Foil 2 errors indicate the metaphorical meaning was at least partially accessed, but incorrectly interpreted. This error pattern suggests that the origin of comprehension failure in cases like 444DX and 642KM is more complex than for patients presenting only a systematic literal bias. Understanding the different ways metaphor comprehension breaks down in the injured brain may enable more appropriate and targeted rehabilitation strategies.

Metaphor deficits are of clinical interest to patients and their caregivers for many of the same reasons as general language impairments, but their effects on communication may be more insidious. For example, metaphor is an attractive option for discussing internal emotional states (*I exploded at the rude customer*), abstract concepts (*The right thing to do is a gray area*) or explaining new, complex ideas (*The brain is a computer*). In these cases, a literal bias would make comprehending the metaphoric statements as they were intended impossible. Yet, as the normal neuropsychological profiles and the patients' own reflections make plain, metaphor interpretation failures do not announce themselves immediately the way literal comprehension deficits do. The abstract nature of the concepts typically expressed by metaphor may contribute to their poor detection in casual conversation. More simply, we are imperfect listeners; if we expect successful comprehension, we are more likely to project it.

Finally, it is worth noting that both patients demonstrating a disproportionate metaphor deficit had unilateral left-hemisphere lesions (384BX, 642KM). Without overstating the importance of lesion location in such a small sample, this observation is inconsistent with the right-hemisphere hypothesis of metaphor, which predicts metaphor impairments in right- not left-hemisphere patients. In accordance with the accumulating evidence from neuroimaging, our data indicate metaphor comprehension is a not solely a right-hemisphere dependent process. Left-hemisphere brain-damaged patients may be in as much need for figurative language rehabilitation as right hemisphere injured patients. Research on the efficacy of therapies targeting metaphor comprehension is not only scarce, but also customarily only targets right-hemisphere patients because of their presumed susceptibility to these kinds of deficits (Lundgren et al., 2006, 2011).

In sum, our results from three illustrative patient cases establish the utility of a carefully designed multiple choice task as a new tool in the investigation of the neural basis of metaphor comprehension. Focal lesion patients were the focus of this investigation, but the approach is equally suitable for investigating questions of metaphor comprehension in other clinical populations or in neuroimaging studies with healthy adults. The metaphor multiple choice task uniquely avoids the methodological and interpretative pitfalls of tasks previously used with patients, while adding increased sensitivity for capturing different types of comprehension deficits. Further, although not the aim of the current study, the inclusion of metaphors of different types enables investigating current, outstanding theoretical questions about the cognitive and neural mechanisms supporting metaphor comprehension. Most importantly, we wish to highlight the clinical utility of our approach. Our task revealed that patients can have figurative language deficits neither evaluated nor predicted by traditional aphasia assessments. This observation raises the possibility that

many patients that might benefit from targeted therapies are currently overlooked. We can not see what our tools are not designed to detect.

### **AUTHOR CONTRIBUTIONS**

The experiment was conceived by Eileen R. Cardillo and Anjan Chatterjee The stimuli were generated by Eileen R. Cardillo. The experiments were programmed and carried out by Geena R. Ianni and Marguerite McQuire Data analysis was done by Geena R. Ianni with assistance from Eileen R. Cardillo and Marguerite McQuire All authors were involved in data interpretation. The paper was written by Geena R. Ianni and revised by Eileen R. Cardillo, Marguerite McQuire and Anjan Chatterjee All authors approved the final version for submission.

### **ACKNOWLEDGMENTS**

This research was supported by a National Institute of Health grant (R01-DC012511) awarded to Anjan Chatterjee, a National Institute of Health training grant (T32AG000255-16), and a University of Pennsylvania College Alumni Society Research Grant awarded to Geena R. Ianni. The authors are particularly grateful to 444DX, 384BX, and 642KM for their participation. We would also like to thank Christine Watson for help with stimuli norming and selection using SOS, and Jonathan Yu, Casey Gorman, and Sam Cason for their assistance with stimuli norming and data collection.

### **REFERENCES**

testing neural hypotheses about metaphor. *Behav. Res. Methods* 42, 651–664. doi: 10.3758/BRM.42.3.651

**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.

*Received: 04 April 2014; accepted: 08 October 2014; published online: 03 November 2014.*

*Citation: Ianni GR, Cardillo ER, McQuire M and Chatterjee A (2014) Flying under the radar: figurative language impairments in focal lesion patients. Front. Hum. Neurosci. 8:871. doi: 10.3389/fnhum.2014.00871*

*This article was submitted to the journal Frontiers in Human Neuroscience.*

*Copyright © 2014 Ianni, Cardillo, McQuire and Chatterjee. 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.*

# Familiarity differentially affects right hemisphere contributions to processing metaphors and literals

**Vicky T. Lai 1\*, Wessel van Dam1 , Lisa L. Conant 2 , Jeffrey R. Binder 2 and Rutvik H. Desai 1\***

1 Department of Psychology, University of South Carolina, Columbia, SC, USA

2 Department of Neurology, Medical College of Wisconsin, Milwaukee, WI, USA

### **Edited by:**

Seana Coulson, University of California at San Diego, USA

### **Reviewed by:**

Bálint Forgács, Central European University, Hungary Tristan S. Davenport, University of California at San Diego, USA

#### **\*Correspondence:**

Vicky T. Lai and Rutvik H. Desai, Department of Psychology, University of South Carolina, 1512 Pendleton Street, Columbia, SC 29208, USA e-mail<EMAIL_ADDRESS><EMAIL_ADDRESS>
The role of the two hemispheres in processing metaphoric language is controversial. While some studies have reported a special role of the right hemisphere (RH) in processing metaphors, others indicate no difference in laterality relative to literal language. Some studies have found a role of the RH for novel/unfamiliar metaphors, but not conventional/familiar metaphors. It is not clear, however, whether the role of the RH is specific to metaphor novelty, or whether it reflects processing, reinterpretation or reanalysis of novel/unfamiliar language in general. Here we used functional magnetic resonance imaging (fMRI) to examine the effects of familiarity in both metaphoric and non-metaphoric sentences. A left lateralized network containing the middle and inferior frontal gyri, posterior temporal regions in the left hemisphere (LH), and inferior frontal regions in the RH, was engaged across both metaphoric and non-metaphoric sentences; engagement of this network decreased as familiarity decreased. No region was engaged selectively for greater metaphoric unfamiliarity. An analysis of laterality, however, showed that the contribution of the RH relative to that of LH does increase in a metaphorspecific manner as familiarity decreases. These results show that RH regions, taken by themselves, including commonly reported regions such as the right inferior frontal gyrus (IFG), are responsive to increased cognitive demands of processing unfamiliar stimuli, rather than being metaphor-selective. The division of labor between the two hemispheres, however, does shift towards the right for metaphoric processing. The shift results not because the RH contributes more to metaphoric processing. Rather, relative to its contribution for processing literals, the LH contributes less.

**Keywords: metaphor, right hemisphere, novelty, familiarity, difficulty, laterality, language, imaging**

### **INTRODUCTION**

Metaphor has been intensely researched for decades, and the view on metaphor has been transformed from it being something poetic reserved for literary use, to something fundamental and generalizable in our daily language and thinking (Lakoff and Johnson, 2003). The pervasiveness of metaphors has been quantified: People use about 5 metaphors for every 100 words of text (Pollio et al., 1990), including 1.8 novel and 4.08 frozen metaphors (e.g., *leg of a table*) per minute of discourse (Pollio et al., 1977). In recent years there has been a surge of interest in studying the neural basis of metaphor, as the answers not only have implications for clinical conditions such as stroke, schizophrenia, and autism, but also have broader impact for understanding the comprehension of language meaning in general.

Perhaps the most debated issue with regard to the neural basis of metaphor is whether the right hemisphere (RH) plays a special role in non-literal language. Several well-known studies reported a special role of the RH in processing metaphors. Winner and Gardner (1977) examined the comprehension of non-literal sentences (e.g., *give me a hand*) in aphasic patients using a sentence-picture matching task. They found that RH patients were less accurate than left hemisphere (LH) patients (accuracies 43% vs. 58%), and suggested that an intact RH is needed for mapping non-literal language meaning onto situations in which it is appropriate (a picture of a person helping others as opposed to a picture of a hand). Bottini et al. (1994) examined the comprehension of new, unusual figures of speech in sentences (e.g., *The investors were squirrels collecting nuts*) in a neurologically healthy sample studied with positron emission tomography. In a semantic judgment task, participants judged whether a given sentence is a plausible metaphor. They compared metaphor and literal conditions and found strongly right-lateralized activation for the metaphor condition in the frontal, temporal, and parietal regions.

However, many functional magnetic resonance imaging (fMRI) studies using neurologically healthy participants have shown that metaphor processing is left lateralized. Rapp et al. (2004) examined novel metaphors in the form of A-is-B (e.g., *Die Worte des Liebhabers sind Harfenklaenge*, "*The lovers' words are harp sounds*") and their literal counterparts (*Die Worte des Liebhabers sind Luegen*, "*The lovers' words are lies*"). In a valence judgment task, participants judged whether a given sentence has a positive or a negative connotation. When compared with a lowlevel baseline, metaphors led to activation in the right inferior frontal gyrus (IFG) and temporal pole. But when compared with literal sentences, the metaphors only showed activations in the LH, in the left lateral IFG, inferior temporal gyrus, and posterior middle temporal gyrus (MTG). Schmidt and Seger (2009) also examined A-is-B metaphors (e.g., *Respect is a precious gem*). Activations for those metaphors relative to literals were found in the left precentral gyrus, temporal pole, inferior parietal lobe, and lingual gyrus. Chen et al. (2008) examined predicate metaphors embedded in a sentence (e.g., *The man fell under her spell*) in contrast with literals (*The child fell under the slide*). The metaphors led to more activation in the LH than in the RH, with the activations in the left IFG, MTG, and angular gyrus (AG), and the right anterior portion of the MTG.

What, then, determines RH involvement in metaphor processing? One of the most studied factors is metaphor novelty/unfamiliarity.1 Electrophysiological studies have shown repeatedly that novel metaphors are processed differently from conventionalized ones (Arzouan et al., 2007; Lai et al., 2009; Lai and Curran, 2013). However, whether this difference is reflected in greater RH involvement is unclear, as electrophysiological metaphoricity effects were very similar between hemispheres (Coulson and Van Petten, 2007). In other studies, novelty has been found to mediate RH activations for metaphors (Mashal et al., 2005, 2007; Stringaris et al., 2006; Schmidt et al., 2007; Pobric et al., 2008). In particular, Faust (2012) proposed that the RH is involved only in novel metaphors, not in conventional metaphors. Mashal et al. (2007) contrasted 2-word conventional (*bright student*) and novel (*pearl tears*) metaphorical expressions with literal (*water drop*) and unrelated (*road shift*) expressions. In a semantic task, participants silently judged if the two words were metaphorically related. Novel metaphors, compared with literals, led to activations in bilateral IFG, right posterior superior temporal gyrus (STG), left middle frontal gyrus (MFG), and middle anterior cingulate gyrus. Conventional metaphors, compared with literals, showed activations in the right postcentral parietal lobe, left posterior STG, and left IFG. Direct comparison between novel and conventional metaphors showed that novelty led to activation in the right posterior superior temporal sulcus (STS), right IFG, and left MFG. Based on these findings, Pobric et al. (2008) conducted a repetitive transcranial magnetic stimulation (rTMS) study to examine the causal role of the right posterior superior temporal region in relation to metaphor processing. They found that rTMS to the right posterior STG impaired the processing of novel metaphors but not conventional metaphors. In contrast, rTMS to the left IFG impaired the processing of conventional but not novel metaphors.