What's left for balanced bilinguals? Language proficiency and item familiarity affect left-hemisphere specialization in metaphor processing

Objective: To characterize the hemispheric processing of metaphors in bilinguals compared with monolinguals and to determine the role of language proficiency in hemispheric lateralization. Method: Fifty-seven English-dominant Spanish-English bilinguals and 57 English speaking monolinguals participated in a divided visual field study. The two groups performed a semantic judgment task with metaphorical, literal, and unrelated word pairs presented either to the right visual field/left hemisphere or to the left visual field/right hemisphere. Results: Bilinguals processed metaphors more slowly and less accurately than monolinguals in both visual field presentations but there was no difference between the groups in the symmetry of processing-both groups showed a left hemisphere advantage. In bilinguals, the efficiency of processing within the left, but not the right, hemisphere was predicted by language dominance scores (i.e., English minus Spanish picture naming scores). Additionally, in all participants, the left hemisphere was more sensitive than the right hemisphere to metaphor familiarity; the latter in turn was sensitive to metaphor familiarity only in balanced bilinguals (not in unbalanced bilinguals and monolinguals). Conclusion: These results suggest that even though bilinguals are less efficient, they rely on the same underlying cognitive mechanisms as monolinguals in linguistic processing of metaphors. Moreover, whereas the right hemisphere is coarsely affected by language proficiency, the left hemisphere, and metaphor processing therein, is more sensitive to small variations in linguistic experience.