Miriam Faust

An fMRI investigation of the neural correlates underlying the processing of novel metaphoric expressions

The neural networks associated with processing related pairs of words forming literal, novel, and conventional metaphorical expressions and unrelated pairs of words were studied in a group of 15 normal adults using fMRI. Subjects read the four types of linguistic expressions and decided which relation exists between the two words (metaphoric, literal, or unrelated). According to the Graded Salience Hypothesis (GSH, ), which predicts a selective RH involvement in the processing of novel, nonsalient meanings, it is primarily the degree of meaning salience of a linguistic expression rather than literality or nonliterality, which modulates the degree of left hemisphere (LH) and right hemisphere (RH) processing of metaphors. In the present study, novel metaphorical expressions represented the nonsalient interpretations, whereas conventional metaphors and literal expressions represented the salient interpretations. A direct comparison of the novel metaphors vs. the conventional metaphors revealed significantly stronger activity in right posterior superior temporal sulcus, right inferior frontal gyrus, and left middle frontal gyrus. These results support the GSH and suggest a special role for the RH in processing novel metaphors. Furthermore, the right PSTS may be selectively involved in verbal creativity.

The role of the right hemisphere in processing nonsalient metaphorical meanings: Application of Principal Components Analysis to fMRI data

Some researches indicate that the right hemisphere (RH) has a unique role in comprehending the figurative meaning of metaphors whereas the results of other studies do not support the notion of a selective role for the RH in accessing metaphorical meanings. The present research used fMRI technology to test a theoretical explanation of the above conflicting findings. This theoretical account is derived from the Graded Salience Hypothesis (GSH) [Giora, R. (1997). Understanding figurative and literal language: the Graded Salience Hypothesis. Cognitive Linguistics, 7, 183-206; Giora, R. (2003). On our mind: Salience, context and figurative language. New York: Oxford University Press], according to which the degree of meaning salience, rather than literality or nonliterality primarily affects differences between the LH and RH in linguistic processing. Thus, the GSH predicts a selective RH involvement in comprehension of novel, nonsalient metaphoric meanings and LH involvement in the comprehension of conventional, salient metaphoric meanings. Fifteen normal adults participated in a block designed fMRI experiment that compared the patterns of brain activation induced by processing the meanings of literal, conventional metaphoric, novel metaphoric and unrelated word pairs. The subjects performed a semantic judgment task. We applied the Principal Components Analysis (PCA) technique in order to find different functional networks corresponding to the different stimuli. Our results, obtained from PCA of the fMRI data indicate that the right homologue of Wernickes area has a special role in processing novel metaphors. We suggest that a unique network, consisting of the right homologue of Wernickes area, right and left premotor areas, right and left insula and Brocas area, is recruited for the processing of novel metaphors but not for the processing of conventional metaphors.

Sentence context and lexical ambiguity resolution by the two hemispheres

A lexical decision experiment investigated hemisphere asymmetries in resolving lexical ambiguity within a sentence context. Sentences that biased a single meaning (either dominant or subordinate) of sentence-final ambiguous words were followed by a lateralized target related to the sentence-congruent or -incongruent meaning of the ambiguous word, or an unrelated word. In the RVF sentence-congruent targets were facilitated, while incongruent targets were not primed. In contrast, related targets were facilitated in the LVF, regardless of sentence context. This suggests that selecting the contextually appropriate word meaning requires the left hemisphere, and supports a right hemisphere role in maintaining alternate word senses.

Cerebral hemispheric asymmetries in processing lexical metaphors

This study investigated semantic priming for literal (stinging-mosquito) and metaphoric (stinging-insult) associates presented to either the left or right visual fields (RVF/LVF) across stimulus-onset-asynchronies (SOA) of 200 and 800 ms. For the short SOA condition, facilitation was found for metaphorically related targets in both visual fields (VFs) while literally related targets were facilitated only in the RVF. For the long SOA condition, metaphorically related targets were facilitated in the LVF whereas literally related targets were facilitated in the RVF. These results support previous findings indicating an enhanced role of the RH in metaphoric comprehension. In addition, the present results are in accordance with current models of hemispheric semantic processing.

The role of the right cerebral hemisphere in processing novel metaphoric expressions taken from poetry: a divided visual field study.

Previous research suggests that the right hemisphere (RH) may contribute uniquely to the processing of metaphoric language. However, most studies have focused on familiar metaphoric expressions. The present study used the divided visual field paradigm to examine the role of the right cerebral hemisphere in processing novel metaphoric expressions taken from poetry. In two experiments, participants were presented with four types of word pairs, literal, conventional metaphoric and novel metaphoric expressions and unrelated word pairs, and asked to perform a semantic judgment task. Two different SOAs: 400 and 1100 ms were used. The results of both experiments showed that responses to LVF/RH presented target words were more accurate and faster than responses to RVF/LH target words for novel metaphoric expressions, but not for other types of word pairs. These results support previous research indicating that during word recognition, the RH activates a broader range of related meanings than the LH, including novel, nonsalient meanings. The findings thus suggest that the RH may be critically involved in at least one important component of novel metaphor comprehension, i.e., the integration of the individual meanings of two seemingly unrelated concepts into a meaningful metaphoric expression.

Semantically convergent and semantically divergent priming in the cerebral hemispheres: lexical decision and semantic judgment.

The effects of semantically divergent and semantically convergent priming on the processing of lexical ambiguity by the two cerebral hemispheres were examined in two visual hemifield experiments. The experiments investigated the ability of the right hemisphere (RH) and the left hemisphere (LH) to summate activation from two single word primes followed by a laterally presented ambiguous target word. In a lexical decision task (experiment 1), the two priming words were either both related to the dominant meaning of the target (new, fresh-NOVEL), or to the subordinate meaning (story, book-NOVEL), or to one dominant and one subordinate meaning (new, story-NOVEL). Results indicated that the LH benefited most from semantically convergent primes that converged onto the dominant meaning of the ambiguous target word, whereas the RH benefited most from semantically mixed (divergent) primes, that diverge on alternate meanings of the ambiguous target word. We used the same stimuli in a semantic relatedness judgment task (experiment 2), and found that the facilitation in the RH was significantly larger when the primes were mixed than when both primes converged on a single (i.e. either dominant or subordinate) meaning of the to-be-presented target word. In contrast, the only facilitation found in the LH was when the two primes were associated with a single meaning (either dominant or subordinate) of the to-be-presented target word. When the primes were mixed, there was no facilitation in the LH. These results support previous findings indicating that during word recognition, the RH activates a broader range of related meanings than the LH, including alternate meanings of ambiguous words. Thus, by summating activation for seemingly incongruous elements, the RH may be critically involved in at least one important component of verbal creativity.

Hemispheric differences in processing the literal interpretation of idioms: Converging evidence from behavioral and fMRI studies

The present study examined the role of the left (LH) and right (RH) cerebral hemispheres in processing alternative meanings of idiomatic sentences. We conducted two experiments using ambiguous idioms with plausible literal interpretations as stimuli. In the first experiment we tested hemispheric differences in accessing either the literal or the idiomatic meaning of idioms for targets presented to either the left or the right visual field. In the second experiment, we used functional magnetic resonance imaging (fMRI) to define regional brain activation patterns in healthy adults processing either the idiomatic meaning of idioms or the literal meanings of either idioms or literal sentences. According to the Graded Salience Hypothesis (GSH, Giora, 2003), a selective RH involvement in the processing of nonsalient meanings, such as literal interpretations of idiomatic expressions, was expected. Results of the two experiments were consistent with the GSH predictions and show that literal interpretations of idioms are accessed faster than their idiomatic meanings in the RH. The fMRI data showed that processing the idiomatic interpretation of idioms and the literal interpretations of literal sentences involved LH regions whereas processing the literal interpretation of idioms was associated with increased activity in right brain regions including the right precuneus, right middle frontal gyrus (MFG), right posterior middle temporal gyrus (MTG), and right anterior superior temporal gyrus (STG). We suggest that these RH areas are involved in semantic ambiguity resolution and in processing nonsalient meanings of conventional idiomatic expressions.

Brainwaves are stethoscopes: ERP correlates of novel metaphor comprehension

The processing of unfamiliar metaphors was examined using event related potentials (ERPs). We compared the patterns of brain electrical activity elicited by processing two-word expressions denoting literal, conventional metaphoric, and novel metaphoric meaning, as well as unrelated word pairs. Participants performed a semantic judgment task in which they decided whether each word pair conveyed a meaningful expression. N400 amplitude to the second word of the pair varied as a function of expression type in a graded manner increasing from literal expressions to conventional metaphors, to novel metaphors and to unrelated pairs. N400s elicited by novel metaphors showed a right-biased scalp distribution as compared to those elicited by conventional metaphors. Novel metaphors also elicited a right-sided late negativity suggesting further attempts to integrate meaning in a non-literal fashion, a result that supports the sequential view of novel metaphor comprehension. These findings are consistent with recent brain imaging studies and complement them by adding the temporal dynamics dimension.

An fMRI study of processing novel metaphoric sentences

Due to inconsistent findings, the role of the two cerebral hemispheres in processing metaphoric language is controversial. The present study examined the possibility that these inconsistent findings may be due, at least partly, to differences in the type (i.e., words vs sentences) or the familiarity of the linguistic material. Previous research has shown that novel two-word metaphoric expressions showed stronger activation in the right homologue of Wernickes area for the novel metaphors than for both literal expressions and unrelated word pairs. In the present study fMRI was used to identify the left (LH) and the right hemisphere (RH) neural networks associated with processing unfamiliar, novel metaphoric sentences taken from poetry, as compared to those involved in processing familiar literal sentences and unfamiliar nonsensical sentences. Across participants, several left lateralised brain regions showed stronger activation for novel metaphoric sentences than for the nonsensical sentences although both types of sentence represent unfamiliar linguistic expressions. Moreover, the metaphoric sentences elicited more activation in the left dorsolateral prefrontal cortex and the posterior middle temporal gyri than did both the literal sentences and the nonsensical sentences. The increased activation in these brain regions might reflect the enhanced demand on the episodic and semantic memory systems in order to generate de-novo verbal semantic associations. The involvement of the left posterior middle temporal gyri could reflect extra reliance on classical brain structures devoted to sentence comprehension.

Linguistic processes in the two cerebral hemispheres: Implications for modularity VS interactionism

Three experiments are reported on lexical decision to target stimuli presented to the right or left visual field (RVF, LVF) following a variety of priming stimuli, words, incomplete sentences, and scrambled sentences. Lexical decision performance is always superior for stimuli presented to the RVF. Primes always facilitate the discrimination of words from nonword target stimuli presented to either visual field. However, when the prime is a sentence which is completed syntactically and semantically by a target word (normal, congruent sentence), the facilitation for RVF presented targets is significantly greater than for LVF targets. When the prime is either: (1) a single word, (2) a nonstructured (scrambled) sentence, or (3) a noncongruent-related sentence, the difference in facilitation between RVF and LVF presented targets is much smaller. These data are discussed with respect to (1) the nature of priming by sentences versus words, (2) language processing by the two hemispheres, and (3) modularity versus interactionism in language processing.