Elsevier

NeuroImage

Volume 36, Issue 1, 15 May 2007, Pages 222-231
NeuroImage

Dynamics of hemispheric activity during metaphor comprehension: Electrophysiological measures

https://doi.org/10.1016/j.neuroimage.2007.02.015Get rights and content

Abstract

Brain imaging studies have lead to conflicting findings regarding the involvement of the right hemisphere (RH) in metaphor comprehension. Some report more relative RH activation when processing figurative expressions but others have shown just the opposite. The inconsistencies might be a result of the low temporal resolution related to current brain imaging techniques which is insufficient to uncover patterns of hemispheric interaction that change over time. Event-related potentials and a source estimation technique (LORETA) were used to investigate such temporal interactions when 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. Our findings indicate that during comprehension of novel metaphors there are some stages of considerable RH involvement, mainly of the temporal and superior frontal areas. Although the processing mechanisms used for all types of expressions were similar and require both hemispheres, the relative contribution of each hemisphere at specific processing stages depended on stimulus type. Those stages correspond roughly to the N400 and LPC components which reflect semantic and contextual integration, respectively. The present study demonstrates that RH mechanisms are necessary, but not sufficient, for understanding metaphoric expressions. Both hemispheres work in concert in a complex dynamical pattern during literal and figurative language comprehension. Electrophysiological recordings together with source localization algorithms such as LORETA are a viable tool for measuring this type of activity patterns.

Section snippets

Electrophysiological measures of lateralized processing of metaphors

People encounter and use metaphoric expressions regularly in their daily lives. Expressions such as “my lawyer is a shark” are not meant to be taken literally and entail an alternative meaning. One of the most interesting issues in language comprehension is whether metaphorical expressions are processed using the same mechanisms that are used for understanding literal meanings. In particular, the involvement of the right hemisphere (RH) in understanding figurative meanings has attracted

Participants

Twenty-nine right-handed native Hebrew speakers participated in the experiment for monetary compensation. Each subject provided written informed consent before participating.

Stimuli

A list of 96 Hebrew two-word expressions (24 per condition) was formed using conventional metaphoric (CM) expressions (e.g., lucid mind, transparent intention), novel metaphors (NM) drawn from poetry texts (e.g., ripe dream, conscience storm), semantically related (LT) words (e.g., burning fire, problem resolution), and

Results

On average participants classified correctly 92.8% (S.D. = 9.8%) of the UR pairs as not meaningful. Expressions were rated as meaningful on average 95.3% (S.D. = 4.6%) for the LT pairs and 95.1% (S.D. = 6.4%) for the CM pairs, and 57.2% (S.D. = 17.8%) of the NM expressions. Reaction times for correctly classified stimuli to LT and CM pairs (M = 873 ms, S.D. = 127, and M = 880 ms, S.D. = 141, respectively) were shorter than to UR pairs (M = 1015 ms, S.D. = 194) which were in turn shorter than to NM pairs (M = 

Discussion

Consistent with our hypothesis, our findings indicate that during comprehension there are some stages of considerable RH involvement in the processing of novel metaphors. Although the processing mechanisms used for all types of expressions were similar, as indicated by similar elicited components and parallel fluctuations in brain volume activation, the relative contribution of each hemisphere at specific processing stages depended on stimulus type. Those stages correspond roughly to the N400

Acknowledgments

The study was performed in partial fulfillment of the requirements for the first author's doctoral dissertation at Bar-Ilan University. The experiments were carried out at the Alter Family Cognitive Psychophysiology Laboratory, Bar-Ilan University.

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