NEURAL SUBSTRATES OF METAPHOR

Rachel Giora and Argyris K. Stringaris

The interest in how the brain processes METAPHORS traces its origins back to a tradition which regarded figurative language as POETIC and hence the opposite of literal language. Despite its ubiquity (Lakoff and Johnson 1980), the underlying assumption has been that this difference should be reflected both in behavioral(Grice 1975; Searle 1979) and brain mechanisms. In this chapter we examine this and other long-standing assumptions, suggesting that the interactions of linguistics with empirical, neuropsychological, and neuroscientific research have drawn a far more complex and, arguably, fascinating picture, not only about metaphor but also about the brain.

Is Metaphor Really So Different?

Since the 1970s,the assumption that metaphors areprocessed differently from literals has come into close scrutiny. For example, on the basis of psycholinguistic experiments, it has been argued that, in the presence of rich and supportive context, metaphors and literals are processed along the same routes (Gibbs 1994; Ortony et al. 1978).

Although some metaphoric and literal expressions require similar processes (Glucksberg 2001), it has also become increasingly evident that the categories used are in themselves heterogeneous. For instance, some literals (the ring was made of tin, with a pebble instead of a gem) require more complex (metaphor-like) conceptual mapping processes than others (That stone we saw in the natural history museum is a gem; Coulson and Van Petten 2002). Others (curl up and dye) are more appealing although harder to process than metaphoric equivalents (curl up and die; Giora 2003). Metaphors are not all alike either: some are novel, having nonsalient metaphoric interpretations that are usually more appealing yet harder to process than those that are conventional and salient (Giora et al. 2004). Furthermore, some metaphoric stimuli, although relatively conventional, may still be more open-ended than others and, when functioning as a context, give rise to a wider range of associations (Stringaris et al. 2006).

In fact, recent findings indicate that notions such as degree of salience, complexity, or open-endedness may be more suitable to describe the complexity of some of the phenomena in question and span the metaphor-literal divide. Furthermore, whilst these notions may, to an extent, overlap, none of them is specific to metaphor.

Is Metaphor Processed Differently in the Brain?

Consistent with the prevailingview of the RIGHT HEMISPHERE (RH) as being more adept at CREATIVITY than the LEFT HEMISPHERE (LH), early lesion studies have been interpreted as evidence that metaphors rely more heavily than their literal counterparts on regions in the RH (Winner and Gardner 1977). However, Winner and Gardner’s study actually reveals that patients with RH lesions were "not insensitive to metaphor" (p. 725) when offering verbal explications to figurative stimuli, although they tended to erroneously select literal over metaphoric interpretations in a picture matching task. Similarly, the results of the earliest imaging study in the field (Bottini et al. 1994) were also seen as supporting a RH predominance for metaphor comprehension. However, alternative explanations may be more appropriate, given that the linguistic items used also differed on categories other than sensu strictu metaphoricity.

Indeed, subsequent studies have challenged the purported predominance of the RH by demonstrating that, when processing conventional metaphors compared to literals, the LH is more active (Ahrens et al. 2007; Lee and Dapretto 2006; Oliveri et al. 2004), perhaps reflecting retrieval from SEMANTIC stores. In fact, most recent research suggests that, in the absence of a rich biasing context, the hemispheres are insensitive to figurativeness. Rather, the RH is more sensitive than the LH to novel, non-salient interpretations and poetic associations, to complexity, and to open-endedness (Blasko and Kazmerski 2006; Giora 2007). This is corroborated by a recent FMRI study, showing that failure to recruit RH areas when processing novel metaphors distinguishes patients with schizophrenia from healthy controls (Kircher et al. 2007).

Taken together, these findings suggest that LATERALIZATION in the brain’s hemispheres is contingent upon factors such as novelty, semantic and conceptual MAPPING complexity, and evoked range of associations, all of which seem to act independently of figurativeness, thus challenging as too simplistic the notion of a preferential RH processing of stimuli solely by virtue of their metaphoricity. These factors, however, are in accordance with an alternative account - the fine-coarse semantic coding hypothesis (Beeman 1998; Jung-Beeman 2005) - which views the LH as adept at processing finely-tuned semantic relations and the RH as specialized in processing distant semantic relationships.

Novelty

Recent studies indicate that the degree of novelty of an expression is an important determinant of neural processing. For instance, lesion studies (Giora et al. 2000; Kaplan et al. 1990), studies of individuals with Alzheimer's disease (Amanzio et al. in press),as well as fMRI studies involving healthy participants (Eviatar and Just 2006) demonstrated that processing non-salient (IRONIC, METAPHORIC) interpretations relied more heavily on the RH; processing conventional (metaphoric) meanings involved the LH. Similarly, a series of fMRI, DVF, and ERP studies demonstrated increased activation of RH areas during processing of nonsalient interpretations of novel metaphors (Arzouan et al. 2007; Faust and Mashal 2006; Mashal and Faust in press; Mashal et al. 2005;Mashal et al. 2007) and literal/compositional interpretations of IDIOMS (Mashal et al. in press). And while RH advantage was demonstrated in processing nonsalient interpretations of novel metaphors during first exposure, repeated exposure benefited the LH (Mashal and Faust 2007).

Complexity

That RH recruitment increases with complex sentences has been demonstrated by a number of studies (Jung-Beeman 2005). This has also been seen as typifying conceptual mapping complexity (Coulson and Van Petten 2002), thus introducing another parameter that may determine processing and operate regardless of metaphoricity. Further work is awaited to establish this.

Range of semantic associations

Range of semantic associations, also termed degree of open-endedness, can be seen as determined by the extent to which a stimulus evokes a wide network of semantic associations (Black 1993). In a fMRI study, Stringaris et al. (2006) showed that deciding that a given probe was unrelated to a previous neutral context triggered activation of frontal RH areas following open-ended (metaphoric) contexts (Some answers are straight) but not following more restricted (literal) contexts (Some answers are emotional). In the case of the open-ended PRIMES, both negative and positive decisions elicited the same neural responses. Indeed, higher degree of open-endedness may lead to increased RH activation, probably because of the evocation of remotely related associations (Jung-Beeman 2005). As shown by Mashal et al. (in press), RH areas were uniquely involved when novel literal interpretations of familiar idioms (involving their familiar idiomatic meanings as well) were deliberated on.

Contextual information

CONTEXTUAL factors involved in processing (such as biasing information, task, mood, or experience) further argue against a specific and invariant brain locus for metaphor (Kutas 2006). They show that recruitment of neural networks depends upon factors other than metaphoricity per se. For instance, in Coulson and Van Petten (2007), RH advantage in processing novel metaphors disappears in the presence of biasing information. In Kacinik and Chiarello (2007), both hemispheres were activated by metaphors, but only the LH-response was context-sensitive, thereby restricting the range of possible alternatives. Conversely, the response in the RH indicated retention of alternatives available for processing. Findings in Rapp et al. (2007) indicate that the type of task is an additional determinant of processing. When participants had to judge the EMOTIONAL valence of connotations, metaphors elicited LH regions, despite their novelty. In Stringaris et al. (2006), familiar metaphors activated RH areas when a coherence judgment was required; however, when a meaningfulness judgment was required, same stimuli evoked LH areas (Stringaris et al. 2007). In Blasko and Kazmerski (2006), it was individual differences in experience that mattered: poets and nonpoets differed in which brain areas were recruited when reading poetry.

In sum, recent research, involving a wide range of methodologies, does not provide support for the long assumed special status of metaphor in language. Instead, it shows that the processing of metaphors in the brain depends on a great number of factors beyond figurativeness.

Works Cited and Suggestions for Further Reading

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Amanzio, Martina, Giuliano Geminiani, Daniela Leotta, and Stefano Cappa. In press. "Metaphor comprehension in Alzheimer's disease: novelty matters." Brain and Language.

Arzouan, Yossi, Abraham Goldstein, and Miriam Faust. 2007. "'Brain Waves are Stethoscopes': ERP Correlates of Novel Metaphor Comprehension." Brain Research 1160: 69-81.

Beeman, Mark. 1998. "Coarse Semantic Coding and Discourse comprehension." In Right Hemisphere Language Comprehension: Perspectives from Cognitive Neuroscience, 255-284, eds. Mark Beeman and Christine Chiarello. Mahwah, NJ: Erlbaum.

Black, Max. 1993. "More about Metaphor." In Metaphor and Thought (2nd ed.), ed. Andrew Ortony. Cambridge, MA: CambridgeUniversity Press.

Blasko, G. Dawn and Victoria A. Kazmerski. 2006. "ERP Correlates of Individual Differences in the Comprehension of Nonliteral Language." Metaphor and Symbol 21(4): 267–284

Bottini, Gabriella., Corcoran Rhiannon, Roberto Sterzi, Eraldo Paulesu, Schenone, P., Scarpa, P. et al. (1994). "The Role of the Right Hemisphere in the Interpretation of Figurative Aspects of Language: A Positron Emission Tomography Activation Study." Brain 117: 1241-1253.

Coulson, Seana and Cyma Van Petten. 2002. "Conceptual Integration and Metaphor Comprehension: An ERP Study." Memory & Cognition 30: 958-968.

Coulson, Seana and Cyma Van Petten. 2007. "A Special Role for the Right Hemisphere in Metaphor Comprehension? ERP Evidence from Hemifield Presentation." Brain Research 1146: 128-145.

Eviatar, Zohar and Marcel Just. 2006. "Brain Correlates of Discourse Processing: An fMRI Investigation of Irony and Metaphor Comprehension." Neuropsychologia 44:2348-2359.

Faust, Miriam and Nira Mashal. 2007. "The Role of The Right Cerebral Hemisphere in Processing Novel Metaphoric Expressions Taken From Poetry: A Divided Visual Field Study." Neuropsychologia45: 860-870.

Gibbs, W. Raymond Jr. 1994. The Poetics of Mind. Cambridge: CambridgeUniversity Press.

Glucksberg, Sam. 2001. Understanding figurative language: From metaphors to idioms. New York: OxfordUniversity Press.

Giora, Rachel. 2003. On our Mind: Salience, Context and Figurative Language. New York: OxfordUniversity Press.

Giora, Rachel, ed. 2007. Is Metaphor Unique? Neural Correlates of Nonliteral Language.Brain and Language 100/2.

Giora, Rachel, Ofer Fein, Ann Kronrod, Idit Elnatan, Noa Shuval, and Adi Zur. 2004. "Weapons of Mass Distraction: Optimal Innovation and Pleasure Ratings." Metaphor and Symbol 19: 115-141.

Giora, Rachel, Eran Zaidel, Nachum Soroker, Gila Batori, and Asa Kasher. 2000. "Differential Effects of Right- and Left-Hemisphere Damage on Understanding Sarcasm and Metaphor." Metaphor and Symbol 15: 63-83.

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Kircher, T .J. Tilo, Dirk T. Leube, Michael Erb, Wolfgang Grodd, and Alexander M. Rapp. 2007. "Neural Correlates of Metaphor Processing in Schizophrenia." NeuroImage 34: 281-289

Kutas, Marta. 2006. "One Lesson Learned: Frame Language Processing – Literal and Figurative – As a Human Brain Function." Metaphor and Symbol 21: 285-325.

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Jung-Beeman, Mark. 2005. "Bilateral Brain Processes for Comprehending Natural Language." Trends in Cognitive Sciences 9: 512-518.

Lee, S. Susan and Mirella Dapretto. 2006. "Metaphorical vs. Literal Word Meanings: fMRI Evidence against a Selective Role of the Right Hemisphere." NeuroImage, 29, 536-544.

Mashal, Nira and Miriam Faust. In press. "Right Hemisphere Sensitivity to Novel Metaphoric Relations: Application of the Signal Detection Theory."Brain and Language.

Mashal, Nira and Miriam Faust. 2007. "Repeated Exposure to Novel Metaphors Affects Hemispheric Involvement." Paper submitted for publications.

Mashal, Nira, Faust, Miriam, Talma Hendler. 2005. The Role of The Right Hemisphere in Processing Nonsalient Metaphorical Meanings: Application of Principal Components Analysis to fMRI Data." Neuropsychologia 43 (14): 2084-2100.

Mashal, Nira, Faust, Miriam, Talma Hendler, and Mark Jung-Beeman. 2007. "An fMRI Investigation of the Neural Correlates Underlying the Processing of Novel Metaphoric Expressions." Brain and Language100: 115-126.

Mashal, Nira, Faust, Miriam, Talma Hendler, and Mark Jung-Beeman. In press. "Processing Salient and Less-Salient Meanings of Idioms: an fMRI Investigation." Cortex.

Oliveri, Massimiliano., Romero, Leonor, and Costanza Papagno. 2004. "Left but Not Right Temporal Involvement in Opaque Idiom Comprehension: A Repetitive Transcranial Magnetic Stimulation Study." Journal of Cognitive Neuroscience 16: 848-55.

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Stringaris, K. Argyris., Nicholas C. Medford, Rachel Giora, Vincent C. Giampietro, Michael J. Brammer, and Anthony S. David. 2006. "How Metaphors Influence Semantic Relatedness Judgments: The Role of the Right Frontal Cortex." NeuroImage 33: 784-793.

Stringaris, K. Argyris., Nicholas C. Medford, Vincent C. Giampietro, Michael J. Brammer, and Anthony S. David. 2007. "Deriving Meaning: Distinct Neural Mechanisms for Metaphoric, Literal, and Non-Meaningful Sentences." Brain and Language 100: 150-162.

Winner, Ellen and Howard Gardner. 1977. "The Comprehension of Metaphor in Brain-Damaged Patients." Brain 100: 717-729.

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