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Neuroscience and Biobehavioral Reviews 30 (2006) 11821205

Review

Neurocognitive mechanisms of figurative language

processingEvidence from clinical dysfunctions

Patrizia Thoma, Irene Daum

Ruhr-University of Bochum, Institute of Cognitive Neuroscience, Department for Neuropsychology, UniversitatsstraXe 150, Bochum 44780, Germany

Received 22 May 2006; received in revised form 25 August 2006; accepted 3 September 2006

Abstract

The interpretation of proverbs has a long tradition in the assessment of abstract thinking, particularly in schizophrenia. Although the

usefulness of proverb interpretation as a diagnostic tool has been questioned over the years, the comprehension of non-literal language

nevertheless plays an important role in social interactions. Thus, researchers remain interested in the neurocognitive mechanisms

mediating comprehension and use of figurative language.

The present paper summarizes and evaluates the evidence from behavioral, lesion and imaging studies including data for compromised

figurative language processing derived from clinical populations. One main focus is on studies of figurative language comprehension in

schizophrenia. Several theoretical explanations proposed to account for the difficulties schizophrenia patients experience when

confronted with figurative language will be addressed. An integration of the evidence from different areas of research is attempted and

directions for future investigation are outlined.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Figurative language; Proverbs; Idioms; Schizophrenia; Right hemisphere

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1183

1.1. Aims and scope of the article . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1183

1.2. Definitions of relevant terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1183

1.3. Main ideas about the mechanisms of figurative language comprehension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184

1.4. The ontogeny of figurative language comprehension. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1185

2. Neurocognitive mechanisms underlying the comprehension of figurative language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186

2.1. Lesion studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186

2.2. Neurophysiological studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1187

2.3. Semantic priming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1189

2.4. Metaphor processing in neurodevelopmental and neurodegenerative non-psychiatric disorders. . . . . . . . . . . . . . . . 11902.4.1. Agenesis of the corpus callosum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1190

2.4.2. Autism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1191

2.4.3. Neurodegenerative diseases involving subcortical structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192

2.4.4. Alzheimers disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1193

2.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1193

3. Figurative language processing in schizophrenia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1193

3.1. Standardized assessment of proverb comprehension in schizophrenia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1194

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3.2. Empirical evidence of impaired figurative language comprehension in schizophrenia . . . . . . . . . . . . . . . . . . . . . . . 1194

3.2.1. Figurative language impairment in schizophrenia: traditional views. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1194

3.2.2. Is the impairment of figurative language comprehension specific for schizophrenia? . . . . . . . . . . . . . . . . . . 1196

3.2.3. The processing of context information and the comprehension of non-literal language in schizophrenia . . . . 1197

3.2.4. The relationship between ToM abilities and figurative language processing in schizophrenia . . . . . . . . . . . . 1197

3.2.5. The role of psychopathology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1198

3.2.6. Impaired figurative language comprehension in schizophrenia: a state or a trait marker?. . . . . . . . . . . . . . . 1198

3.3. Conclusions and implications for further research in schizophrenia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11994. General summary and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200

1. Introduction

1.1. Aims and scope of the article

Non-literal expressions form an integral part of everyday

language, conveying features of the conventional wisdom,

social norms and rules characterizing a given society

(Gibbs and Beitel, 1995). A great deal of our everyday

communication is figurative rather than literal with figures

of speech occurring at an estimated rate of about 6 per

minute of speech (Pollio et al., 1977). Most people find

non-literal language easy to understand presumably

because most of their thinking is conceptualized through

metaphor, proverbs, irony and other instances of non-

literal language (Lakoff and Johnson, 2004).

The ability to effectively use figurative communication

may promote personal and professional success. In healthy

adolescents, for instance, idiom comprehension has been

positively associated with academic achievement (Nippoldand Martin, 1989). On the other hand, the inability to

efficiently cope with this form of communication may

substantially contribute to the poor social competence of

individuals suffering from disorders like schizophrenia

(Mitchell and Crow, 2005;Vallance and Wintre, 1997).

Acknowledging the relevance of non-literal language for

social interaction, an increasing amount of research has

addressed the neurocognitive mechanisms mediating the

processing of non-literal language. The present review

primarily aims to summarize and critically evaluate the

evidence derived from a range of cognitive neuroscience

methods. In the first section, relevant terms and definitions

will be introduced, a brief outline of the available theories

about the cognitive and linguistic mechanisms underlying

figurative language comprehension will be given and the

development of non-literal language comprehension across

the lifespan will be briefly described. In the second section,

evidence of impaired figurative language processing in

neurodevelopmental and neurodegenerative disorders will

be reviewed. The third section addresses impaired figura-

tive language comprehension in schizophrenia, the disorder

in which this topic has been comprehensively investigated.

A summary of the most relevant findings and suggestions

for future investigations will be outlined in the concluding

section.

1.2. Definitions of relevant terms

It has proved surprisingly difficult to elaborate the

distinction between literal and non-literal language

(Glucksberg, 2001). Two major criteria have been estab-

lished. First, literal statements are supposed to express a

truth (e.g. Tim is in Canada.) while non-literal language

usually expresses a falsehood (e.g. Tim is on cloud nine),

although this distinction has not remained without contra-

diction (Gibbs and Beitel, 1995). Second, literal language

confirms to linguistic constraints while non-literal language

tends to violate them. For instance, in the sentence This

car is very thirsty. the linguistic constraint regarding the

use of the adjective thirsty is violated, because only

creatures can be thirsty (Fass, 1999).

Although the terms non-literal and figurative

language are sometimes used synonymously, the term

figurative language originally applies only to expressions

containing figures of speech or metaphors, which arenot necessarily involved in all non-literal statements (e.g.

Where theres a will theres a way) (Gibbs and Beitel,

1995). A metaphor can be constituted by a single word, a

phrase, a sentence or a whole text and makes an explicit

(My love is like a fever.) or implict (My life is a roller-

coaster ride) comparison between ideas from different

knowledge domains which are usually not associated

with one another (Gibbs, 1999; Glucksberg, 2003). To

put it more strongly, metaphors not only compare certain

unrelated categories with one another but also make

class inclusion assertions by attributing salient properties

of one category to another (Glucksberg and Keysar,

1990). Most neuroscience research focuses on figurative

language rather than on non-figurative, non-literal lan-

guage because it occurs more frequently in everyday

interactions and because its comprehension is supposed

to place higher demands on cognitive abilities (Lakoff and

Johnson, 2004).

This review will also focus predominantly on the

comprehension of metaphors in general and particularly

in association with proverbial and idiomatic expressions.

Research dealing with irony will be taken into account to a

lesser extent, because additional cognitive factors, like the

adequate perception of affective prosody, play a greater

role in the interpretation of irony (Wang et al., 2006).

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Sarcasm, humor and indirect requests will be not or only

marginally addressed.

Proverbs and idioms are among the most common

instances of everyday non-literal communications (Gibbs

and Beitel, 1995). Both do not represent a unitary class of

expressions. Proverbs may be broadly defined as familiar,

fixed, sentential expressions that communicate well-knowntruths, social norms, or moral concerns (Gibbs and Beitel,

1995). They are often characterized by certain lyrical

elements (e.g. rhyme, meter, alliteration, personification)

and specific syntactic structures (e.g. where theres X,

theres X or no X without X). The more of these typical

markers a proverb contains, the easier it is accepted as

such. For a comprehensive analysis of proverbs and their

characteristics see the article by Gibbs and Beitel (1995).

Due to the very heterogeneous nature of proverbial

statements and a lack of appropriate classification dimen-

sions, neurocognitive studies have mostly treated proverbs

as a unitary concept, at best distinguishing between

familiar and unfamiliar proverbs.

In the investigation of idiom comprehension, distinctions

between different classes of idioms have been taken into

account more often. Idioms are phrases whose figurative

meaning is not simply constituted by the literal meanings of

their individual words (Cacciari and Tabossi, 1988;

Cacciari and Glucksberg, 1991). For instance, the con-

stituents of the idiom Its raining cats and dogs! evoke

the association of a heavy rain shower only within this

special contextual configuration, while the words cats,

dogs and raining presented in isolation do not. Idioms

vary with respect to their literal plausibility, composition-

ality and transparency/opacity (Glucksberg, 2001). Am-biguous idioms may be plausible both in a figurative and

in a literal sense, (e.g. to kick the bucket) while literally

implausible idioms (to be on cloud nine) make only sense

when interpreted figuratively. Compositionality relates to

the extent to which the meanings of the words constituting

the idiom provide clues for its figurative meaning. While

the words forming the idiom to talk a mile a minute

easily connote speech rate, kick the bucket represents an

instance of a non-decomposable idiom (Gibbs et al., 1989).

The terms transparency/opacity are often used synony-

mously with compositionality: With transparent idioms, in

contrast to opaque idioms, speakers may easily recover the

motivation for the figures of speech used. These dimen-

sions, along with contextual bias, affect the ease of idiom

acquisition and comprehension: While decomposable

idioms are acquired in a rather context-independent way,

non-decomposable idioms rely more on contextual infor-

mation (Gibbs and Nayak, 1989).

In using irony, the speaker usually wants to convey the

opposite of what he says. The true speaker intention can be

often only identified with the help of specific context

information and often there is nothing inherently figurative

about the statement per se except that it is falsified by

context information (e.g. What lovely weather we have

when it is raining) (Gibbs, 1994).

As will be outlined in subsequent sections, partially

distinct neurocognitive mechanisms seem to mediate the

understanding of metaphors, idioms, proverbs and irony.

1.3. Main ideas about the mechanisms of figurative language

comprehension

A detailed account of theories dealing with figurative

language comprehension is far beyond the scope of this

article and only some of the main ideas will be introduced.

Interesting reviews have been for instance provided byFass

(1999),Glucksberg (2001)andLakoff and Johnson (2004).

Theories about the relative contributions of the two

hemispheres and those trying to explain figurative language

impairments of clinical populations will be addressed in the

corresponding sections in the text.

Specific theories have been put forward to explain the

processing of each subtype of figurative expressions.

However, most of these theories address the same hotly

debated issue applying to figurative language comprehen-

sion in general and relating to the question of the order in

which the literal and figurative meanings of a figurative

expression are accessed and whether both are always

accessed at all. Traditional views give priority to the literal

meaning suggesting that the search for a figurative meaning

begins only after the literal meaning has been rejected, e.g.

on the basis of context information (hierarchical hypoth-

esis) (Clark and Lucy, 1975). An example of this view is the

Idiom List Hypothesis (Bobrow and Bell, 1973) accord-

ing to which the meanings of idioms are stored in a kind of

list from which they are retrieved whenever the literal

meaning is judged to be inappropriate. The parallelhypothesis states that both kinds of meanings are processed

at the same time (Glucksberg et al., 1982), illustrated e.g.

by the Lexical Representation Hypothesis (Swinney and

Cutler, 1979) according to which idioms are represented as

long complex words. The retrieval of their meaning is

supposed to take place at the same time as the lexical

processing of the expression. Similarly, according to the

Configuration Hypothesis (Cacciari and Tabossi, 1988),

the idiomatic meaning is activated as soon as active

analysis of the word configuration has prompted the

recognition of the idiomatic nature. By contrast, Gibbs

and Beitel (1995) propose that the literal meaning is

bypassed altogether and that the figurative meaning is

accessed immediately. They state that e.g. understanding

proverbs basically involves mapping of information from

familiar source concepts onto vaguer target domains/

concepts (Conceptual Metaphor Hypothesis). All these

hypotheses tacitly assume an intact lexico-semantic system

as basis for figurative language comprehension.

What is relevant for the direction of this review is the

question which other higher-order cognitive mechanisms

might be important for figurative language processing. The

concept of pragmatics, which is the study of how people

use and interpret linguistic utterances in conversations,

provides one answer. Grice (1957; 1975; 1978; 1989)

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proposed that human communication is always based on

the expression and mutual understanding of the inter-

locutors intentions and introduced the Cooperative

Principle. It states that speakers usually make their

conversational contribution such as is required, at the

stage at which it occurs, by the accepted purpose or

direction of the talk exchange (Grice, 1989, p. 26) inwhich they are engaged. The Cooperative Principle

encompasses a number of maxims such as Avoid

obscurity, Do not say that for which you lack adequate

evidence, Make your contribution as informative as is

required and Be relevant. Grice (1975) assumed that

what is communicated or implied may deviate considerably

from what is literally said (conversational implicature)

which obviously particularly applies to metaphoric, idio-

matic, proverbial speech and other instances of non-literal

language. Sperber and Wilson (1995) developed Grices

ideas (1957; 1975; 1978; 1989) further introducing Re-

levance Theory. According to the Communicative

Principle of Relevance, a speaker communicates only

what he thinks will be worth to claim his interlocutors

attention. Sperber and Wilson (2002) emphasize that for

successful communication, people have to be able to go

beyond the sentence meaning and to infer what kind of

meaning their interlocutors intend to convey. The general

ability to form an adequate concept of other peoples

mental states (thoughts, feelings, wishes, beliefs and

intentions) in order to be able to understand their actions

has been called having a Theory of Mind (ToM)

(Premack and Woodruff, 1978), mentalizing (Frith et al.,

1991; Langdon and Coltheart, 1999) or mind-reading

(Baron-Cohen, 1995). The term ToM will be used inthis article. First-order ToM tasks assess the ability to infer

another persons thoughts or beliefs about the state of the

world. Second-order ToM tasks require the subject to infer

one persons thoughts (beliefs) about another persons

thoughts about the state of the world. First-order ToM

competence emerges around ages 34 while second-order

ToM competence does not develop until the age of 67

years (Baron-Cohen, 1995), depending on the social

environment (Carpendale and Lewis, 2004). However, as

the underlying neuronal correlates of ToM, mainly the

prefrontal cortex (PFC) and temporal lobe structures, are

not fully maturated until adolescence, ToM also undergoes

further development (seeSinger, 2006). As outlined below,

there is considerable evidence confirming Sperbers and

Wilsons proposal that ToMor to be more specific: a

specialized submodule of ToMis critically involved in

inferring figurative meanings. The authors also proposed

that comprehending different types of figurative language

depends on distinct ToM processes. Understanding meta-

phors, basically a descriptive use of language, is supposed

to involve inferring how another person sees the world, i.e.

first-order ToM. By contrast, comprehension of irony,

which represents an interpretative use of language, requires

the recognition that the interlocutor distances himself from

the way a third person sees the world (i.e. by saying Yeah,

what lovely weather for a picnic! after another person has

suggested a picnic although it is raining), which involves

second-order ToM (Sperber and Wilson, 2002). Some

authors argue (e.g. Brune and Bodenstein, 2005) that

although the majority of proverbs are metaphorical, they

also rather form an instance of interpretative language, as

most implicitly convey social norms, rules and behavioralinstructions.

Besides ToM, executive control function (ECF) might be

relevant for figurative language comprehension. Distinct

fronto-subcortical circuits seem to support ECF (Heyder et

al., 2004), which is thought to orchestrate and coordinate a

set of complex cognitive abilities, like inhibition, multi-

tasking, context processing, response selection and plan-

ning, in order to ensure flexible and adaptive goal-directed

behavior (see Royall et al., 2002). Similarly to ToM,

executive abilities are not fully maturated until adolescence

(Paus, 2005). It is evident from this brief description of the

ECF concept that the ability to process multiple meanings

at the same time, to choose the appropriate one taking into

account context information as well to suppress inap-

propriate literal meaningsrelevant for figurative lan-

guage comprehensionmight be related to specific ECF

subcomponents. Corresponding evidence will be consid-

ered throughout the text.

1.4. The ontogeny of figurative language comprehension

Children develop the ability to understand figurative

language gradually during childhood, from the age of 34

years on, and adolescence (Nippold et al., 1988a), usually

making literal interpretation errors at first (Lodge andLeach, 1975).

Two of the hypotheses introduced earlier have been

predominantly put forward to explain the development of

figurative language competence: The Configuration Hy-

pothesis (Cacciari and Tabossi, 1988) predicts an earlier

understanding of figurative expressions that are easier to

decompose for active analysis. This has been demonstrated

for concrete relative to abstract proverbs (Nippold and

Haq, 1996) and for transparent relative to opaque idioms

(Nippold and Rudzinski, 1993;Nippold and Taylor, 1995,

2002). But there is also evidence for the view that idiom

meanings are acquired in the form of giant lexical units

(Swinney and Cutler, 1979) similarly to the meaning of

single lexical items: Relative to younger children, older

children and adults depend less on context information for

idiom comprehension and provide appropriate figurative

idiom interpretations even when the context strongly biases

their literal meaning (Ackermann, 1982). This indicates

that they have stored representations of their figurative

meanings, probably due to greater experience with non-

literal language.

According to the Language experience hypothesis

comprehension develops through exposure to non-literal

expressions in everyday discourse or during formal

training. It has even been suggested that people learn the

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meanings of proverbs, idioms and metaphors in a rote

manner (Lodge and Leach, 1975) establishing an associa-

tive link between a non-literal expression and its figurative

meaning. Evidence comes from a number of studies

demonstrating that familiar proverbs or idioms are easier

and earlier comprehended than unfamiliar figurative

expressions (Cunningham et al., 1987; Nippold and Haq,1996;Nippold and Rudzinski, 1993;Nippold and Taylor,

2002;Penn et al., 1988).

The development of the ability to appraise the meaning

of non-literal statements appears to be associated with the

maturation of a number of related cognitive abilities. For

instance, the development of mental images evoked by

figurative phrases appears to support their comprehension.

Accordingly, school-age children report less sophisticated,

less comprehensive and more concretistic mental images of

idiom content than adults (Nippold and Duthie, 2003).

Context information (e.g. a background story) has been

found to facilitate the comprehension of the figurative

meaning of both proverbs (Nippold et al., 1988b) and

idioms (Cain et al., 2005; Nippold and Martin, 1989) in

school-age children and in adolescents. In younger children

(3.56.5 years) context does not aid idiom comprehension

(Abkarian et al., 1992) which might be partly due to the

fact that idiom-in-context comprehension seems to depend

on general reading comprehension skills (Levorato et al.,

2004), particularly for more difficult idioms. A study by

Cain et al. (2005)showed that 9-year-old children were able

to benefit from context information for the interpretation

of transparent idioms regardless of their reading compre-

hension level. However, poor reading comprehenders were

impaired in their ability to use context for the interpreta-tion of opaque idioms.

Most importantly, the development of figurative language

comprehension seems to be associated with the ontogeny of

ToM competence. This is e.g. illustrated by the fact that

metaphors are comprehended at an earlier age (ages 34)

than irony (ages 67) (Bara and Bucciarelli, 1998; Happe,

1993; Winner, 1988) which is in accordance with Sperbers

and Wilsons (2002)account of the differential involvement

of first- and second-order ToM in the comprehension of

metaphor and irony. The developmental trajectories of first-

and second-order ToM seem to parallel those of metaphor

and irony comprehension.

Only one study investigated proverb comprehension

across the whole lifespan (Nippold et al., 1997): The ability

to freely explain the meaning of proverbs (low-familiar,

within a story context) improved during adolescence and

early adulthood and reached a peak during the 20 s which

remained stable until the 50s. A slight decline in

performance was observed during the 60 s which became

statistically significant in the 70s. Due to the cross-

sectional design of the study, a cohort effect, possibly

involving lower formal education for the older patients,

cannot be excluded. Education has repeatedly been shown

to be positively related to figurative language comprehen-

sion (Penn et al., 1988).

The detrimental impact language disorders can have on

overall life achievement is illustrated by a study investigat-

ing the longitudinal course of developmental language

disorder in a group of affected men from middle childhood

to mid adulthood (Clegg et al., 2005). In mid adulthood,

the language disordered group showed significant impair-

ments of ToM, verbal short-term memory and phonologi-cal processing, significantly worse social adaptation (few

close friendships and love relationships as well as

prolonged unemployment) and a higher incidence of

mental illness relative to their siblings and a group of

typically developing subjects.

2. Neurocognitive mechanisms underlying the

comprehension of figurative language

Different methods have been used in order to gain

insight into the neural mechanisms supporting the proces-

sing of figurative language. The investigation of patients

suffering from selective brain lesions or specific neurologi-

cal and neuropsychiatric disorders, advanced imaging

techniques and behavioral studies involving divided visual

field research contributed both in combination and

independently to the available knowledge base about the

neural correlates of figurative language comprehension. In

the following paragraphs the main findings are summar-

ized.

2.1. Lesion studies

Traditionally, while the left hemisphere (LH) has been

viewed as dominant for most aspects of language proces-sing, the understanding of figurative language has been

thought of as being lateralized to the right hemisphere

(RH) (seeBookheimer, 2002). This notion has been largely

based on a series of studies examining figurative language

processing in patients suffering from unilateral brain

damage (Burgess and Chiarello, 1996; Critchley, 1991;

Gagnon et al., 2003; Giora, 2003; Joanette et al., 1990;

Kemper, 1981;Van Lancker and Kempler, 1987;Weylman

et al., 1989).

One prototypical task involves the matching of orally

presented or written figurative expressions (e.g. His heart

fealt heavy) and their appropriate pictorial illustrations.

Patients with RH damage (RHD) have been reported to

choose the pictures depicting the literal (e.g. a man carrying

a giant heart) instead of the figurative meaning (e.g. picture

of a very sad man) of such expressions more often than

either LH damaged (LHD) patients or healthy individuals

(Hillekamp et al., 1996;MacKenzie et al., 2005;Schmitzer

et al., 1997;Winner and Gardner, 1977). It has been argued

that in sentence-to-picture matching tasks, the depicted

alternative meanings often do not show the same degree of

plausibility (Huber, 1990) and that visuo-spatial abilities,

which are more affected in RHD vs. LHD patients, ought

to be considered as a potential confounding variable. The

RH has been ascribed an important role in visuospatial

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analysis (Jordan and Hillis, 2005) and in the allocation of

cognitive resources (Monetta et al., 2006). Thus, damage of

this hemisphere might limit the cognitive capacities for the

analysis of alternative figurative meanings rendering

patients more prone to choosing the less demanding

and more obvious (literal) illustration of the figurative

utterance.A major purely linguistic approach is the word triad

relatedness paradigm. In this task, subjects are presented

with sets of three words: an ambiguous word (e.g. the

adjective cold), its figurative equivalent (unfriendly)

and a foil representing its literal meaning (chilly).

Participants are then asked to group together the two

words that are closest in meaning. The result pattern

mostly resembled the one obtained in sentence-to-picture

matching tasks: RHD patients were more likely to select

the literal foils and less often chose the figurative

interpretations than both LHD patients and healthy

individuals (Brownell et al., 1984, 1990;Brownell, 1998).

The poor performance of RHD patients on figure

interpretation tasks has been related to the suppression

deficit hypothesis (Tompkins and Lehman, 1998) accord-

ing to which RHD patients fail to suppress automatically

activated literal interpretations of ambiguous expressions

that eventually turn out to be irrelevant or incompatible

with the available contextual information. This is sup-

ported by impairments of RHD patients on resolving

lexical ambiguity, e.g. choosing between the figurative and

the literal meaning of ambiguous words/expressions, by

suppressing contextually inappropriate interpretations

(Grindrod and Baum, 2005; Klepousniotou and Baum,

2005;Tompkins et al., 2000).However, not all studies support the notion that

figurative language processing deficits are selectively

associated with RHD. LHD patients have been reported

to make more errors when requested to orally explain the

meaning of conventional metaphors (e.g. broken heart,

hard man) with a literally implausible meaning (Giora et

al., 2000). Also, LHD patients have been shown to be

impaired relative to healthy controls on a sentence-to-

picture matching task for idiomatic expressions without a

literal meaning (Papagno et al., 2004) and more frequently

than RHD patients chose the literal interpretation of

ambiguous targets in a word triad relatedness task (Giora,

2003). Performance on the latter task and lesion size were

negatively associated only in LHD patients (Zaidel et al.,

2002). It has been proposed that LHD patients, similarly to

RHD patients, might fail to suppress the literal interpreta-

tion of a figurative expression (Papagno et al., 2004).

Cacciari et al. (2006) used a sentence-to-word matching

task to assess the comprehension of ambiguous familiar

Italian idioms in aphasic LHD patients and healthy

controls. Each idiomatic expression was presented along

with four words and subjects were instructed to choose the

word corresponding to the idiomatic meaning of the

expression. One of the three foils was semantically

associated with the last constituent word of the idiom

string and the two remaining alternatives were unrelated

foils. Patients, especially those with frontal and/or tempor-

al lesions, were significantly impaired on this task,

particularly showing a higher number of semantically

associate errors. According to the authors, this might

indicate an impairment of inhibition mechanisms and/or of

recognition/activation of the idiomatic meaning. The data,however, did not allow for a distinction between these

alternatives. In other studies, both LHD and RHD patients

showed impairments (Chobor and Schweiger, 1998; Gag-

non et al., 2003; Tompkins, 1990; Tompkins et al., 1992).

Aphasia has been suggested as a potential factor con-

tributing to the unexpected deficits of LHD patients either

by disrupting speech output on oral explanation tasks or

by impairing semantic comprehension as in Wernickes

aphasia (Gagnon et al., 2003). Thus, the type of the task

may have an impact. Papagno and Caporali (2006) found

that LHD patients performed relatively better on a

sentence-to-word matching task than on a sentence-to-

picture and an oral definition task for idioms.

Generally, the interpretation of findings from brain-

lesioned patients is limited by the frequent co-occurrence of

various medical comorbidites, diverse cognitive impair-

ments and heterogeneous lesion etiologies.

Repetitive transcranial magnetic stimulation (rTMS)

offers the opportunity to temporally and reversibly disrupt

the activity of specific areas in the otherwise intact brain. In

an rTMS study by Oliveri et al. (2004), magnetic

stimulation was applied to frontal and temporal cortex

areas in the RH vs. LH while 15 young healthy subjects

were working on a sentence-to-picture matching task for

opaque idioms and literal expressions. Left temporal rTMSdisrupted both accuracy and response speed for both

idiomatic and literal expressions, whereas no such effect

was obtained after rTMS over the RH. The authors

conclude that the left temporal cortex contributes to the

understanding of both literal and idiomatic expressions.

Taken together, the evidence available from lesion

studies is inconsistent, suggesting that damage to both

hemispheres may affect the comprehension of figurative

language. However, it is unclear in how far differing testing

modalities might have influenced the performance of RHD

and LHD patients. Also, various additional factors, which

seem not to have been taken into account in most lesion

studies, might have influenced the result pattern. These

factors will be introduced in the subsequent paragraphs.

2.2. Neurophysiological studies

Functional neuromaging studies, using PET, fMRI or

EEG explicitly aim to identify networks of brain regions

involved in the processing of figurative language.

Bottini et al. (1994) carried out a PET study in which

they assessed brain activity while individuals judged the

plausibility of visually presented sentences with either a

metaphorical or literal meaning. Novel, unconventional

metaphors were used, such as The old man had a head full

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of dead leaves (plausible) in contrast to The old man had

a head full of barn doors (implausible). Judging the

plausibility of literal sentences (e.g. Tim used stones as

paperweights. vs. Tim used feathers as paperweights.)

as compared to deciding whether a non-word was present

in a string of words activated a number of regions in the

LH including the PFC and basal frontal cortex, the middleand inferior temporal gyri and temporal pole, the parietal

cortex and the precuneus. Judging the plausibility of

metaphorical vs. literal sentences, in addition to activating

these LH regions, also recruited the equivalents of Brocas

and Wernickes in the RH. It has been pointed out that the

involvement of the RH might not be specific to the

processing of figurative language but might occur each time

complex syntactic and/or semantic linguistic structures are

processed (Bottini et al., 1994;Jung-Beeman, 2005;Lee and

Dapretto, 2005; Rapp et al., 2004; Stringaris et al., 2005),

including making references (Beeman, 1993; Mason and

Just, 2004) and structuring complex text information

(Marini et al., 2005). This would fit in with Bottinis

(1994) report that her subjects found it more difficult to

judge the plausibility of metaphorical sentences as opposed

to literal sentences. Rapp et al. (2004) used novel

metaphorical and literal sentences strictly parallelized for

syntactic and semantic complexity. Metaphorical expres-

sions elicited the strongest activation in the left inferior

frontal and left temporal gyri. The authors conclude that

while the RH might contribute to the general appreciation

of complex semantic and syntactic structures, left frontal

and temporal areas might engage in the decoding of word

meaning in a metaphoric context.

Subsequent imaging studies confirmed the activation offronto-temporal networks during the processing of figura-

tive language. For instance, Lee and Daprato (2005)

presented auditory word triads to subjects who were

instructed to decide whether the last two words had a

similar meaning (either metaphoric or literal). Direct

comparison of the two conditions yielded significant

activity only in left prefrontal and temporo-parietal areas.

In a study by Stringaris et al. (2005), subjects were

presented with either metaphoric, literal or non-meaningful

sentences. Left inferior frontal gyrus and BA47 were

activated while participants were reading both the meta-

phorical and the meaningless sentences, but not while they

were reading literal sentences. Additionally, activation of

the left thalamus was specifically linked to the processing of

metaphorical sentences, which is not surprising, given the

close fronto-subcortical connectivity patterns (Alexander et

al., 1986).

Recent data indicate differential hemispheric activity for

different types of figurative language, such as methaphor

and irony (Eviatar and Just, 2006). Young healthy students

read short stories which ended with either a literal,

metaphoric or ironic statement, followed by simple yes/

no comprehension questions. Conventional and non-ironic

metaphoric expressions were used (e.g. the statement You

are like greased lightning by one story character after she

was left far behind by her friend in a race). The ironic

endings did not contain metaphors and always expressed

the opposite of what the story character really meant (e.g.

Thanks for keeping your promise when in reality the

promise has been broken). Processing of metaphors elicited

significantly higher activation in the left inferior frontal

gyrus and in bilateral temporal cortex than ironic andliteral utterances. Irony activated the right superior and

middle temporal gyri more than literal statements did,

while metaphoric utterances elicited an intermediate level

of activation in these areas.

In event-related potential (ERP) studies of language

comprehension, a negative component peaking around

400 ms after stimulus onset (Tartter et al., 2002) has been

shown to vary according to the semantic content of the

information processed. The component is elicited by all

meaningful words and the amplitude of the N400 increases

if a word is unexpected in a given context (Kutas and

Hillyard, 1980).

Reading out sentences with a metaphoric ending has

been shown to evoke an increase in the N400 amplitude

relative to a condition which involved the processing of

literal sentence endings (Coulson and Van Petten, 2002).

Pynte et al. (1996)presented evidence supporting a context-

dependent account of metaphor comprehension. They

recorded ERPs while subjects were reading familiar (e.g.

Those fighters are lions) or literal control sentences

(Those animals are lions). The terminal word, which was

always identical under both conditions, elicited a larger

N400 amplitude when it was embedded in metaphoric as

compared to literal sentences, indicating that the literal

meaning of the metaphors was accessed, but obviouslyjudged to be incongruous in the metaphoric sentence

context. In subsequent experiments, unfamiliar metaphors

were introduced (Those apprentices are lions) and

sentences were preceded by an irrelevant (They are not

idiotic: Those fighters are lions) or a relevant (They are

not cowardly: Those fighters are lions) context or were

presented in isolation. The authors were able to demon-

strate an effect of context which became obvious as early as

300 ms following the onset of the final word. More

precisely, the understanding of the metaphoric meaning

was facilitated in the relevant context condition which was

reflected in a reduction of the N400 amplitude. This

supports the idea that only the metaphorical meaning is

accessed if primed by the context.

Although in thePynte et al. (1996) study, the manipula-

tion of familiarity vs. unfamiliarity failed to elicit any clear

effects, more recent evidence suggests that familiar and

unfamiliar metaphorical expressions might indeed be

processed differently in the brain. In one study (Tartter et

al., 2002), 80 sentence frames that plausibly ended with

either a literal, a familiar metaphoric or a truly anomalous

(novel and unfamiliar) word were presented to 11 subjects.

A significant N400 was elicited only for anomalous

endings. This effect has been investigated further by

Laurent et al. (2005). They recorded ERPs from 30 adults

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who performed a lexical decision task to a series of either

strongly or weakly salient (i.e. familiar and predictable)

idioms and to figurative or literal interpretations of these

idioms. The N400 amplitude following the last word of the

weakly salient idioms was larger than for the strongly

salient (familiar) idioms indicating that the terminal word

was less expected in the novel idiom context. Also, theN400 amplitude in the condition involving targets related

to the salient meaning of a strongly salient idiom was

smaller than in the remaining combinations of salient/non-

salient meanings of strongly/weakly salient idioms and

subjects responded faster to salient interpretations. The

authors interpret their findings in terms of an automatic

accessibility of salient meanings, independent of their

figurative or literal character. This indicates that salient

meanings are processed directly, based on entries in the

mental lexicon without the necessity to make inferences

based on linguistic or extra-linguistic context information.

Sotillo et al. (2005) carried out a source analysis of the

N400 associated with metaphor processing. In their task,

novel metaphoric expressions (e.g. green lung of the city)

were followed by words that were either metaphorically

(park) related or not related (semaphore) to the

expressions. The analyses yielded a larger N400, originat-

ing from the right but not the left superior/middle temporal

gyrus, for the metaphorically related words relative to the

non-related words.

These findings are in line with the Graded Salience

Hypothesis of language comprehension, put forward by

Giora (2003). According to this theory, the more salient

meanings of linguistic utterances are processed before less

salient ones. The more conventional, frequent, prototypicala meaning is, the more salient it is. Non-salient meanings

are supposed to be more dependent on context for their

derivation, processed predominantly in the RH. Evidence

for a differential processing of novel and familiar items in

terms of neuroanatomical localization came from two

fMRI studies by Mashal et al. (2005a, b). Healthy subjects

were presented with 96 word pairs and had to decide

whether the two words forming each pair were unrelated

(road-shift), literally related (water-drops) or meta-

phorically related. In the metaphorical condition, either

conventional metaphors (bright-student) or novel meta-

phors, mostly taken from poetry (pearl-tears) were used.

The data suggest that a specialized network comprising the

right homolog of Wernickes area, right and left premotor

areas, right and left insula and Brocas area, is recruited for

the analysis of novel but not of conventional metaphors.

Some of these brain areas have also been implicated in

verbal creativity (right homolog of Wernickes area: e.g.

Jung-Beeman et al., 2004) and in the retrieval of informa-

tion from long-term episodic memory (right precuneus: e.g.

Grasby et al., 1993; Shallice et al., 1994). These processes

are likely to be involved in inferring the meaning of novel,

unfamiliar connections of words, as found in novel

metaphors. Results consistent with those by Mashal et al.

(2005a, b) have also been reported for the processing of

metaphors in Mandarin Chinese (Ahrens et al., 2005). In

contrast to the processing of familiar metaphors, novel

metaphoric expressions yielded bilateral activation in the

middle frontal gyrus and the precentral gyrus, and RH

activation in the superior frontal gyrus. LH activation was

found in the inferior frontal gyrus and fusiform gyrus.

Taken together, the evidence yielded in imaging studiessuggests that the processing of figurative language con-

sistently activates fronto-temporal networks known to be

involved in language processing per se. As to the question

of lateralization, both hemispheres contribute to the

processing of figurative language, albeit in different ways.

The RH appears to be relatively more involved in

processing complex syntactic and semantic structures and

in accessing the meaning of novel or generally salient

metaphors, while the LH seems to contribute more to the

decoding of word meaning in a metaphoric context.

Some authors did not find an RH advantage for novel

metaphors (Rapp et al., 2004, 2006). However, their stimuli

had not been previously rated for familiarity, so it cannot

be excluded that at least some might have been familiar to

subjects and were thus best processed by the LH. In the

work by Mashal and colleagues (2005a, b), both hemi-

spheres were involved in processing novel metaphors.

However, they used metaphorical word dyads, while

studies in which the processing of novel metaphors was

more clearly lateralized to the RH (Bottini et al., 1994;

Sotillo et al., 2005) used metaphors in a sentence context.

The latter is probably more ecologically valid and places

greater demands on the capacity of the RH to integrate

distant semantic meanings within a sentence context (Jung-

Beeman, 2005).

2.3. Semantic priming

A fairly large body of literature deals with the issue of

lateralized figurative language processing based on the

semantic priming approach in healthy subjects. For a more

detailed overview, the interested reader is referred to the

reviews byNeely (1991)and Hutchison (2003).

The common procedure entails the selective presentation

of prime-target pairs to the right visual field/LH or to the

left visual field/RH. In most cases, a lexical decision task

follows (Chiarello, 1991). Priming effects occur as the

faster recognition of a target word preceded by a

semantically related prime or the slowing of responses to

words following unrelated prime words.

Anaki et al. (1998) presented metaphorical or literal

associates to either visual field as subjects performed a

lexical decision task (word/non-word judgments). The

priming stimuli consisted of ambiguous words with a

literal and a metaphoric meaning (e.g. the adjective

stinging). Target words were either related to the

metaphoric (stinging-insult) or to the literal (stinging-

mosquito) meaning of the prime or they were unrelated

(stinging-carpet). At shorter stimulus onset asynchronies

(SOA of 200 ms) priming effects were observed for

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metaphorically related targets for both visual fields/hemi-

spheres while literally related targets were primed in the

right visual field/LH only. At longer stimulus onset

asynchronies (SOA of 800 ms) metaphorically related

targets were primed only in the left visual field (i.e. the

RH) and literally related targets again only in the right

visual field/LH. The implications of a slower decay offigurative meanings in the RH are that this hemisphere

seems to be involved in the more advanced and more

elaborated stages of figurative language processing. Over-

all, the findings suggest that metaphoric meanings decay

relatively fast in the LH while being maintained for longer

periods of time in the RH. Faust and Weisper (2000)

presented incomplete priming sentences (e.g. Some nights

arey) followed by literally true, false or metaphoric

target words to subjects who were instructed to decide

whether the sentences were literally true or false. In this

study, performance was slower and less accurate for

metaphorical target words than for literally false targets,

irrespective of the hemisphere to which the stimuli were

presented. The two studies differ in the mode of presenta-

tion of figurative material (in isolation vs. in sentence

context) and there is evidence that context may differen-

tially affect processing in the two hemispheres. Data by

Kacinik and Chiarello (2005)suggest that the way the LH

integrates both literal and figurative meanings is more

constrained by the sentence context, while the RH is more

independent of sentence context and also maintains the

activation of alternative interpretations.

The interpretations put forward by Anaki et al. (1998)

and byKacinik and Chiarello (2005)largely correspond to

the coarse semantic coding hypothesis, first proposed byBeeman (1998). According to this account, the RH is

responsible for diffusely activating large semantic fields,

while the LH strongly activates selective semantic fields.

This is assumed to render the LH very efficient at selecting

the most common or contextually appropriate meanings,

particularly for single words, while the RH is more

sensitive to distant semantic overlap, particularly in the

case of multiple word meanings. Support for the coarse

semantic coding hypothesis comes from a number of

divided visual field experiments in healthy populations

(Coney and Evans, 2000;Faust et al., 2002; Titone, 1998).

Another divided field study (Schmidt et al., 2005) suggests

that the RH advantage for processing distant semantic

relationships is more a result of familiarity than of

metaphoricity per se. In this study, regardless of whether

the sentences used as stimuli were literal or metaphorical,

the unfamiliar sentences containing distant semantic

relationships (e.g. metaphorical: The close friends were

a bag of toffees. or literal: The interior designer used

cubes as a rain hat.) were preferentially processed in the

RH and familiar sentences involving close semantic

relationships (e.g. metaphorical: The mind is a sponge.

or literal: The childrens shoes were covered in dirt.) in

the LH. Finally, Klepousniotou and Baum (2005) at-

tempted to contrast the predictions of both the coarse

semantic coding and the suppression deficit (described

earlier in this article) hypotheses by examining LHD and

RHD patients as well as healthy participants using a

semantic priming paradigm. The data did not provide

strong support for either theory, but the result pattern was

more consistent with the suppression deficit hypothesis.

To summarize, the evidence yielded in semantic primingexperiments, similarly to that resulting from lesion and

neurophysiological studies, suggests that the RH seems to

be more engaged in activating distant semantic associa-

tions. Thus, the RH also activates more alternative

interpretations, particularly in the case of unfamiliar

figurative expressions and maintains their activation for

longer time periods.

2.4. Metaphor processing in neurodevelopmental and

neurodegenerative non-psychiatric disorders

Deficits in interpreting figurative language have been

reported for a range of neurodevelopmental and neurode-

generative diseases. The evaluation of these findings is

limited by certain factors. First and foremost, multiple

brain systems are affected in most of these conditions. In

neurodevelopmental disorders, the atypical development of

brain structures may entail some reorganization processes

which influence the way language is processed. Notwith-

standing these limitations, the analysis of these cases can

provide important information about the neurocognitive

processing of figurative expressions in the intact brain.

2.4.1. Agenesis of the corpus callosum

Given that both hemispheres make specific contributionsto the processing of figurative language, it seems obvious

that interhemispheric information transfer might be a

critical mechanism for understanding non-literal language.

Accordingly, it has been reported that patients with

congenital or acquired agenesis of the corpus callosum

are impaired in providing appropriate verbal interpreta-

tions of proverbs and in recognizing the correct proverb

meaning in multiple choice tests. Comprehension of literal

language, on the other hand, appears to be preserved (Paul

et al., 2003). This might be due to partial information

transfer via subcortical pathways or non-callosal commi-

sures, which might partly compensate for callosal absence

for literal language processing, while it is insufficient for

the more complex integration processes involved in

figurative language comprehension (seeBarr and Corballis,

2002). Reorganization processes might also play a role in

this respect (e.g. Sauerwein and Lassonde, 1994).

Figurative language comprehension does not seem to be

generally impaired; deficits occur when more elaborate

context processing is required. Consistent with this view,

children and adolescents (age ranges 718 years) with either

complete agenesis or hypoplasia (i.e. partial or mild

agenesis) of the corpus callosum performed relatively well

with regard to the comprehension of decomposable idioms,

which are processed similarly as literal language, but failed

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to understand non-decomposable idioms, which require the

integration of contextual information (Huber-Okrainec et

al., 2005). In this study, familiar idioms varying on the

dimensions of compositionality (in how far the lexical items

of the idiom contribute to its overall figurative meaning)

and literality (how plausible an idiom is) were presented

verbally, either in an isolated sentence (Shelly hit thesack) or preceded by a context sentence biasing the

figurative meaning of the idiom (Shelly had a long day.

Shelly hit the sack.). Subjects were asked to indicate

whether a picture illustrating either the figurative or the

literal meaning of the idiom, represented the idiom or not.

Children with callosal abnormities were particularly

impaired in terms of both speed and accuracy at accepting

the figurative meaning of non-decomposable idioms and in

rejecting their literal meaning. The impairment was most

pronounced in individuals with complete agenesis.

Adults with complete agenesis of the corpus callosum

have also been reported to perform more poorly than

controls on tests assessing the understanding of humorous

material. However, covarying comprehension of figurative

language abolished the group difference suggesting a

common mechanism probably involving the understanding

of second-order ToM (Brown et al., 2005).

Taken together, evidence suggests that the corpus

callosum mediates the understanding of second-order

meanings, probably via the integretation of relevant

context information. The fact that both children and

adults suffering from agenesis are similarly impaired with

regard to figurative language comprehension implies that

developmental reorganization processes cannot completely

compensate for the impaired interhemispheric connectivityand its detrimental consequences for figurative language

processing.

2.4.2. Autism

It seems obvious that individuals suffering from general

communication disorders, like those from the autistic

spectrum, might have particular difficulties with complex

linguistic demands including the comprehension of figura-

tive language.

Strandburg et al. (1993) observed an ERP correlate of

impaired idiom processing in adults with high-functioning

autism (IQ scores480). Subjects completed an idiom

recognition task involving literal, idiomatic and non-sense

phrases. Autistic subjects were impaired only with regard

to the identification of idiomatic statements and showed a

greatly reduced N400 amplitude to idioms. Dennis and

colleagues (2001) found subjects with a high-functioning

variant of autism to be impaired on the Figurative

Language subtest from the Test of Language Competence

(Wiig and Secord, 1989). In this task, subjects are first

asked to explain a figurative remark preceded by some

context information, e.g. The situation is two boys talking

at a dog show. One of them said He is crazy about that

pet. What did the boy mean?. Subsequently, 4 written

sentences are presented and the subject has to point out the

one that could be used instead of He is crazy about the

pet. Autistic subjects more often failed to find the correct

alternative expression. However, only 8 subjects were

examined in this study and within-group variation of

verbal IQ scores and language skills was rather high.

Several authors have attempted to elucidate the mechan-

isms which mediate deficient figurative language compre-hension in autistic spectrum disorders. The most

commonly suggested factors are impairments of ToM

and ECF, particularly context processing deficiencies.

In an early study,Happe (1994)found that the ability to

provide adequate mental state attributions for the figura-

tive statements of story characters was comprised in high-

functioning autistic subjects, both relative to mentally

retarded subjects and healthy controls. The autistic

subjects comprehension of figurative utterances was

related to their performance on standard ToM tasks. But

even those subjects who performed well on the ToM tasks

had difficulties with interpreting the more complex and

more naturalistic figurative story material. Data by Nor-

bury (2004) suggest that in children with communication

disorders, the question whether context information

improves idiom comprehension might be independent of

the presence of autistic features. Unfamiliar idioms were

presented, first in isolation and, after a delay of 324 h,

embedded in a short-story context. Both children with

communication disorders and control participants per-

formed significantly better in the idiom-in-context condi-

tion than in the idiom-only condition. However, clinical

subgroups exhibiting language impairment (with or with-

out autistic features) benefited significantly less from

context than controls or a group of children showingautistic features but no language impairment. Idioms-in-

context performance was predicted by age, memory for

story context and language abilities. ToM, despite being

impaired at least in subgroups of autistic children (Abdi

and Sharma, 2004), did not contribute significantly to

idiom interpretation, once general language abilities were

controlled for. In another study, in which this factor has

not been covaried, ToM abilites proved critical for the

capacity of high-functioning autists to understand non-

literal language (Martin and McDonald, 2004). The

findings by Norbury (2004) suggest that general language

impairment and not autistic features per se may be the

critical feature mediating the impairment of figurative

language comprehension in autism. Deficient figurative

language comprehension in non-autistic children with

language impairment has been reported earlier (Lee and

Kamhi, 1990).

Landa and Goldberg (2005) were interested in the

relationship between figurative language comprehension

and ECF in autism. They assessed 19 children (ages 717)

diagnosed with idiopathic, high-functioning autism and a

matched control group of 19 children with inconspicuous

development. The figurative language subtest from the test

of language competence (Wiig and Secord, 1989) was

employed to assess comprehension and interpretation of

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metaphoric expressions and figures of speech. Also,

standardized measures of basic language abilities, as the

adequate use of semantics, grammar, morphology and

syntax, were administered. Three subtests from the Cam-

bridge Neuropsychological Test Automated Battery (Cam-

bridge Cognition, 1996) were selected in order to assess

planning, flexibility and spatial working memory as ECFmeasures. Overall, the performance of autistic participants

was heterogeneous, ranging from intact to impaired

language skills and ECF. As a group, autistic subjects

were impaired relative to the non-autistic children on

measures of expressive grammar, comprehension of fig-

urative language, spatial working memory and planning.

The data suggest that both the inability to comprehend

figures of speech (as assessed by sentence-to-picture

matching tasks) and the inability to give a verbal

interpretation of non-literal language may independently

contribute to deficient performance on tasks assessing

figurative language skills. As there were no correlations

between IQ, ECF and language abilities in the autistic

subgroup, the authors conclude that their data do not

support the idea of ECF as a core deficit in autism which

might mediate the observed language impairments. This

conclusion has recently been questioned. In a study by

Rajendran et al. (2005) individuals diagnosed with

Asperger syndrome and healthy peers participated in a

computer-mediated dialog which was part of a scenario

involving figures of speech and sarcasm or inappropriate

requests. Here, verbal and executive abilities as well as

clinical diagnosis predicted comprehension of figures of

speech. The dialog task in this study was possibly more

demanding than the matching and interpretation tasksused in the work by Landa and Goldberg (2005). In the

dialog situation, subjects might have had to rely more on

ECF in order to process different (context) information at

the same time and to self-structure and flexibly respond to

changing demands.

Taken together, individuals suffering from communica-

tion disorders from the autistic spectrum appear to be

impaired in processing non-literal language, although,

within-group variation is rather high. It remains unclear

whether the deficit is possibly mediated by an impairment

of general language abilities, verbal memory, ToM and/or

ECF, regardless of the presence of autistic features.

Inconsistent methodologies and heterogeneous patient

samples make it difficult to draw firm conclusions at this

point.

2.4.3. Neurodegenerative diseases involving subcortical

structures

The PFC, which has been implicated in figurative

language processing (see previous sections), is densely

interconnected with subcortical structures.Alexander et al.

(1986) described three main fronto-subcortical circuits

thought to subserve cognition: The first circuit comprises

the interconnections between the dorsolateral PFC, the

dorsolateral caudate nucleus and the lateral globus

pallidus, which project back to the dorsolateral PFC via

the dorsomedial nucleus of the thalamus. The second loop

involves the orbitofrontal cortex, which is linked to the

ventromedial caudate nucleus and the medial globus

pallidus, as well as backprojections to the orbitofrontal

cortex via the dorsomedial thalamus. The third circuit

connects the anterior cingulate, the basal ganglia andthalamic nuclei. Furthermore, in a frontocerebellar circuit,

the dorsolateral PFC and the lateral cerebellum are

interconnected via reciprocal pathways involving the

pontine nuclei, the dentate nucleus and the thalamus

(Daum and Ackermann, 1997;Schmahmann, 2004). These

fronto-subcortical connections have been shown to con-

tribute to cognitive functions, particularly to ECF (Heyder

et al., 2004). It is thus plausible to assume that subcortical

structures also might participate the processing of non-

literal language.

Support for an involvement of subcortical structures in

figurative language processing comes from a study showing

that patients suffering from olivo-ponto-cerebellar atrophy

were impaired relative to healthy controls in a proverb

interpretation task (Arroyo-Anllo and Botez-Marquard,

1998).Chenery et al. (2002)investigated basic and complex

language abilities in Huntingtons disease which involves

neurodegeneration of the head of the caudate nucleus and,

to a lesser extent, of the globus pallidus and putamen

(Zakzanis, 1998). The comprehension of non-literal lan-

guage was assessed by means of the ambiguous sentences

and figurative language subtests from the Test of

Language Competence (Wiig and Secord, 1989). Overall,

the performance pattern of the Huntington patients and a

group of patients with stroke-induced focal lesions of non-thalamic subcortical structures was comparable, with basic

language abilities being relatively preserved in comparison

with a neurologically intact control group. However,

deficits emerged on tasks assessing lexico-semantic abilities,

word fluency and the interpretation of ambiguous and

figurative language. Both patient groups tended to provide

only one meaning of the ambiguous sentences and to stick

to the literal meaning of figurative utterances, regardless of

the context information provided. This is consistent with

earlier observations by Wallesch et al. (1983) that basal

ganglia patients are unable to provide adequate explana-

tions of idiom meanings.

Monetta and Pell (2006) reported impaired comprehen-

sion of figurative sentences in Parkinsons disease (PD), in

which neurodegeneration affects primarily dopaminergic

neurons in the substantia nigra (Fahn and Sulzer, 2004).

Primetarget sentence pairs were presented to subjects with

the prime sentences being either metaphorical (Those

babys cheeks are roses) or literal (Those flowers are

roses.). Target sentences were either metaphor-relevant,

i.e. referred to a property relevant to the metaphorical

interpretation (That babys cheeks are roses./Roses are

often red.) or metaphor-irrelevant (Roses have

thorns.). PD patients were impaired in terms of both

accuracy and response speed in deciding whether the

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metaphorical sentences made sense or not, but only if they

also showed an impairment of verbal working memory

span. This indicates that in PD, the disruption of complex

language functions such as figurative language comprehen-

sion might be ascribed to limited working memory

capacity.

Altogether, the available evidence from populations withneurodegenerative diseases affecting subcortical structures

suggests a potential participation of the basal ganglia and

the cerebellum in the comprehension of figurative lan-

guage. However, further support from patients with focal

subcortical lesions and from neuroimaging studies is

needed in order to elucidate which substructures are

precisely involved, the nature of their contribution and

the relationship of figurative language impairment to the

disruption of other higher-order cognitive functions.

2.4.4. Alzheimers disease

Conflicting evidence has been reported for figurative

language comprehension in patients suffering from mild to

moderate Alzheimers disease (AD). While Kempler et al.

(1988)reported that from the early stages of the disease on,

AD patients have difficulty in understanding abstract

meanings, Papagno and Vallar (2001) concluded that

decline of figurative language comprehension occurs at

later stages with idiom comprehension being preserved

longer than metaphor comprehension. In a subsequent

study (Papagno et al., 2003), patients with mild probable

AD were administered a sentence-to-picture matching task

for idiomatic and literal phrases. All patients had difficulty

in choosing the correct picture illustrating the figurative

(instead of the literal) meaning of the idiomatic expres-sions. Performance on this subtask correlated with that in a

paper-and-pencil dual task (Baddeley et al., 1997) em-

ployed as ECF measure. However, when, as an alternative

to the picture illustrating the figurative meaning of the

idiom, an unrelated situation was shown, performance

significantly improved. AD patients also performed better

when asked to verbally explain idiomatic interpretations

than when they were administered the sentence-to-picture

matching task used in the first experiment. This effect was

ascribed to the lack of an externally presented literal

interpretation in the oral task. In the few cases that literal

interpretations were provided in the oral task, they

represented plausible real-world situations. The authors

suggest that, although AD patients still retain knowledge

of the figurative meaning of the idiom, they are unable to

suppress its literal interpretation, which is concurrently

activated. These findings also illustrate that performance

on figurative language tasks can vary as a function of the

testing modality.

In summary, it remains unclear, in which stage of AD,

an impairment of figurative language comprehension

begins to show. The knowledge about figurative meanings

appears to be preserved and a deficit in suppressing

alternative literal interpretations of metaphoric expressions

might underlie the impairment. This is in line with the

suppression deficit hypothesis proposed to explain the

poor figurative comprehension of RHD patients (see

Section 2). The fact that in AD, the RH seems to be

affected by neuropathological changes earlier and to a

greater extent than the LH, completes this picture

(Shinosaki et al., 2000).

2.5. Summary

Taken together, the available evidence suggests that

networks involving fronto-temporal cortical areas as well

as subcortical structures (left thalamus, caudate nucleus,

substantia nigra, cerebellum) in both hemispheres con-

tribute to the processing of figurative language. While the

RH seems to be more involved in processing the context in

which a figurative expression appears (Brownell et al.,

1986; Foldi et al., 1983;Tompkins et al., 2001), the LH is

responsible for processing propositional information (Long

and Baynes, 2002). Relative to the LH, the RH seems to

maintain more alternative interpretations of figurative

expressions and does so for longer time periods. Also, the

RH is more concerned with processing non-salient (i.e.

novel) metaphoric meanings. Both hemispheres support the

integration of the figurative expression within the overall

literal message, and interhemispheric communication

transfer via the corpus callosum seems to be critically

involved in this process.

An impairment of figurative language comprehension

has been observed across a range of neurodevelopmental

and neurodegenerative disorders like autism, Chorea

Huntington, Olivo-ponto-cerebellar atrophy, PD and

AD. However, for each of these disorders, even amongpatients allegedly presenting with the same clinical status,

interindividual variability is high, ranging from preserved

to impaired figurative language comprehension. A more

specific characterization of these differentially affected

patient subgroups is clearly needed. It remains as yet

unclear to which degree the mechanisms proposed to

mediate the deficit in figurative language processingsuch

as impaired general verbal abilities, ToM or compromised

ECFcontribute to the observed impairments. In parti-

cular, it is of interest which cognitive subcomponents

contribute to the understanding of figurative language and

in what way they are impaired in different populations.

3. Figurative language processing in schizophrenia

Disorders of thought and language are considered a core

symptom of schizophrenia. Since Finckh (1906) and

Benjamin (1944), researchers and clinicians have regarded

proverb interpretation as a potential tool assisting in the

diagnosis of disordered thinking in patients suffering

from this debilitating mental illness (see Reich, 1981).

Asked to explain the meaning of proverbs, schizophrenia

patients tend to stick to the literal meaning of the

expressions, a clinical phenomenon which since Bleuler

(1911, 1966) has been known as concretism. In clinical

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settings, assessments of proverb interpretation have rarely

been implemented in a systematic way, leading some

authors to question the reliability and validity of proverb

interpretation for diagnostic purposes (Andreasen, 1977;

Reed, 1968). However, systematic investigation of figura-

tive language comprehension in schizophrenia has the

potential to provide important insights into thoughtpatterns of schizophrenia patients. The review article by

Mitchell and Crow (2005) highlights the importance of

pragmatic abilities such as figurative language comprehen-

sion for general interpersonal skills of schizophrenia

patients.

As far as the neurocognitive underpinnings of figurative

language processing in schizophrenia are concerned, direct

evidence is scarce. Currently, findings point towards

disrupted activity of cortico-subcortical circuitry (Buchs-

baum, 1990; Kubicki et al., 2003; Ragland et al., 2004;

Velakoulis and Pantelis, 1996) during the processing of

verbal material, reduced cerebral asymmetry (Sommer et

al., 2003) and impaired interhemispheric communication

transfer due to callosal abnormities (Innocenti et al., 2003)

in schizophrenia patients. As these networks have been

implicated in the processing of figurative language, it is

plausible to assume that patients affected by schizophrenia

have difficulty in interpreting this form of communication.

3.1. Standardized assessment of proverb comprehension in

schizophrenia

In schizophrenia research, standardized proverb com-

prehension tests and standardized scoring criteria have

been applied more often than in studies involving otherpatient groups or healthy individuals. Thus, a brief

description of these methods will be given at this point.

Until now, Gorhams pioneering proverbs test (Gorham,

1956a) has remained the best known standardized diag-

nostic tool for the assessment of proverb comprehension in

the English-speaking world. The test comprises a multiple-

choice part and three parallel forms of a free-answer

version. In the free-answer version, the subject is instructed

to explain the meaning of twelve proverbs. The multiple-

choice version consists of 40 proverbs with four possible

response alternatives representing various interpretations

of the proverb in question. As expected, it is more difficult

to give proverb interpretations in a free-answer format

compared to the multiple-choice version. In schizophrenia

patients, the free-answer version is also more likely to elicit

psychotic material (Gorham, 1956b).

A major problem with the free-answer format consists in

defining an appropriate scoring system. The most common

scoring indices which have been established over the years

distinguish between abstract and concrete (Gorham,

1956a, b), literal (Hertler et al., 1978) as well as bizarre-

idiosyncratic (Marengo et al., 1986) or autistic (Shimku-

nas et al., 1967) features of proverb interpretations. In

Gorhams terms (Gorham, 1956a, b), abstraction is

synonymous with accuracy, while a proverb interpretation

is to be scored as concrete if it fails to replace central

symbols by more abstract terms. Gorham adopted a three-

point scoring system (2: adequate response; 1: partially

correct; 0: complete failure). However, these criteria have

been repeatedly criticized as being too vague (Gibbs and

Beitel, 1995). For instance, not all parts of a proverb

necessarily have a metaphorical character. Therefore, thesewords/phrases do not need to be rephrased in abstract

terms when an interpretation of the proverb is required.

Apart from that, evidence by Shimkunas et al. (1966)

indicates that abstractness and concreteness seem to

reflect general intelligence rather than characteristic fea-

tures of schizophrenic psychopathology.

Hertler et al. (1978) view literalness as more specific

and more independent of overall intellectual ability than

concreteness. They broadly define literalness as an

active attempt to interpret the words of the proverb as a

literal message rather than as symbols to be interpreted.

Finally, bizarre-idiosyncratic or autistic interpreta-

tions are obviously bizarre and unrelated to the proverb

(Shimkunas et al., 1967). On the basis of clinical ratings,

Shimkunas et al. (1967) developed a three-point scoring

manual comprising examples of autistic and non-autistic

proverb interpretations. In schizophrenia patients, bizarre

proverb interpretations are neither associated to concrete-

ness (Marengo et al., 1986;Shimkunas et al., 1967) nor to

general IQ (Shimkunas et al., 1966). In a sample of 80

schizophrenic patients, autistic scores were observed to

decrease over treatment, from admission to 26-week post-

admission (Shimkunas et al., 1967). Abstract and concrete

scores remained unchanged, except in schizophrenia

patients with a high general IQ (Shimkunas et al., 1966).

3.2. Empirical evidence of impaired figurative language

comprehension in schizophrenia

3.2.1. Figurative language impairment in schizophrenia:

traditional views

Goldstein (1944) and Benjamin (1944) were among the

first authors to put forward the idea that the problems of

schizophrenia patients with proverb interpretation might

arise from the inability to assume an abstract attitude,

i.e. to transgress the immediately given specific aspect or

sense impression and to realize that a specific thing

represents an accidental sample or representative of a

category (Goldstein, 1944, p. 18). Benjamin (1944)

analyzed proverb interpretations given by schizophrenia

patients. For instance, as an explanation of the proverb

When the cats away, the mice will play a schizophrenia

patient suggested If there isnt any cat around, the mice

will monkey around, and maybe get into things.

(Benjamin, 1944, p. 73). This led Benjamin (1944) to

conclude that schizophrenia patients are unable to infer

the abstract meaning of the symbols used in proverbs

sticking to their literal meaning instead. Similarly,Goldstein

(1944) reported that the inability of schizophrenia patients

to abstract from a given example manifested itself not only

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group, the input disruption might have already progressed

too far to be overcome by the enrichment procedure. On

the other hand, employing a slightly different approach,de

Bonis and colleagues (1997) did not find any correlation

between the performance of schizophrenia patients in a

proverb interpretation task and global illness severity, as

indexed by the overall score on the Brief Psychiatric RatingScale (BPRS:Overall and Gorham, 1988).

The tendency of schizophrenia patients to be concretistic

in their interpretation of figurative language has been

demonstrated in further studies. Schizophrenia patients

were shown to provide literal rather than figurative

interpretations of metaphorical and ironic remarks (Cut-

ting and Murphy, 1990;Drury et al., 1998), to select literal

rather than figurative pictorial illustrations of metaphoric

utterances (Anand et al., 1994) and to show a lack of

semantic priming for metaphorically rather than literally

related prime target pairs (Spitzer, 1997).

Preliminary evidence suggests that an impairment of

figurative language competence might be a very early feature

of ps

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