Lexical processing in the bilingual brain: Evidence from grammatical/morphological deficits

Background: A few studies have recently documented cases of proficient bilingual individuals who, subsequent to neural injury, suffered selective deficits affecting specific aspects of lexical processing. These cases involved disruption affecting the production of words from a specific grammatical category (verbs or nouns) or the production of irregular versus regular verb forms. Critically, these selective deficits were manifested in a strikingly similar manner across the two languages spoken by each of the individuals. Aims: The present study aims at reviewing these cases of selective cross-linguistic deficits and discussing their implications for theories concerning lexical organisation in the bilingual brain. Methods & Procedures: The studies reviewed here employed a variety of behavioural tests that were specifically designed to investigate the availability in aphasic patients of lexical information concerning nouns and verbs and their morphological characteristics. Outcomes & Results: The brain-damaged bilingual speakers reviewed in the present study exhibited selective deficits for nouns, verbs, or irregularly inflected verbs in both of their languages. Conclusions: The selectivity and cross-language nature of the deficits reviewed here indicates that at least certain language substrates are shared in proficient bilingual people. The fact that these deficits affect grammatical class distinctions and verb inflections-information that is part of the lexicon-further indicates that shared neural substrates support lexical processing in proficient bilingual people.