Metaphorical language processing and amygdala activation in L1 and L2.

The present study aims to investigate the neural correlates of processing conventional figurative language in non-native speakers in a comparison with native speakers. Italian proficient L2 learners of German and German native speakers read conventional metaphorical statements as well as literal paraphrases that were comparable on a range of psycholinguistic variables. Results confirm previous findings that native speakers show increased activity for metaphorical processing, and left amygdala activation increases with increasing Metaphoricity. At the whole-brain level, L2 learners showed the expected overall differences in activation when compared to native speakers (in the fronto-temporal network). But L2 speakers did not show any distinctive activation outside the caudate nucleus as Metaphoricity increased, suggesting that the L2 speakers were less affected by increasing Metaphoricity than native speakers were. With small volume correction, only a single peak in the amygdala reached threshold for L2 speakers as Metaphoricity increased. The findings are consistent with the view that metaphorical language is more engaging for native speakers but not necessarily for L2 speakers.

Affective and psycholinguistic norms for German conceptual metaphors (COMETA).

Figurative expressions have been shown to play a special role in evoking affective responses, as compared to their literal counterparts. This study provides the first database of conceptual metaphors that includes ratings of affective properties beyond psycholinguistic properties. To allow for the investigation of natural reading processes, 64 natural stories were created, half of which contained two or three conceptual metaphors that relied on the same mapping, whereas the other half contained the metaphors' literal counterparts. To allow for tighter control and manipulation of the different properties, 120 isolated sentences were also created, half of which contained one metaphorical word, which was replaced by its literal rendering in the other half. All stimuli were rated for emotional valence, arousal, imageability, and metaphoricity, and the pairs of metaphorical and literal stimuli were rated for their similarity in meaning. A measure of complexity was determined and computed. The stories were also rated for naturalness and understandability, and the sentences for familiarity. Differences between the metaphorical and literal stimuli and relationships between the affective and psycholinguistic variables were explored and are discussed in light of extant empirical research. In a nutshell, the metaphorical stimuli were rated as being higher in emotional arousal and easier to imagine than their literal counterparts, thus confirming a role of metaphor in evoking emotion and in activating sensorimotor representations. Affective variables showed the typical U-shaped relationship consistently found in word databases, whereby increasingly positive and negative valence is associated with higher arousal. Finally, interesting differences between the stories and sentences were observed.

Conventional metaphors in longer passages evoke affective brain response.

Conventional metaphorical sentences such as She's asweetchild have been found to elicit greater amygdala activation than matched literal sentences (e.g., She's akindchild). In the present fMRI study, this finding is strengthened and extended with naturalistic stimuli involving longer passages and a range of conventional metaphors. In particular, a greater number of activation peaks (four) were found in the bilateral amygdala when passages containing conventional metaphors were read than when their matched literal versions were read (a single peak); while the direct contrast between metaphorical and literal passages did not show significant amygdala activation, parametric analysis revealed that BOLD signal changes in the left amygdala correlated with an increase in metaphoricity ratings across all stories. Moreover, while a measure of complexity was positively correlated with an increase in activation of a broad bilateral network mainly involving the temporal lobes, complexity was not predictive of amygdala activity. Thus, the results suggest that amygdala activation is not simply a result of stronger overall activity related to language comprehension, but is more specific to the processing of metaphorical language. SIGNIFICANCE STATEMENT: This work is the first to show that conventional metaphorical language in naturalistic longer passages that includes a range of metaphors elicits more activation in the amygdala-an area recognized to be involved in emotional processing-than carefully matched literal control passages. We probe this finding with parametric analyses using a measure of syntactic complexity and subjective judgments of metaphoricity. While complexity correlates with more overall bilateral activation of the temporal lobes, it does not correlate with amygdala activation. Instead, amygdala activation correlates with metaphoricity, suggesting that the increase in emotional salience is specific to metaphoricity and is not simply a result of an overall increase in brain activity in regions associated with language comprehension.