Perceptual Experience and Spoken Word Recognition

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The goal of the proposed research is to discover how perceptual experience affects the spoken word recognition processing system. This research capitalizes on wide individual differences in linguistic experience among prelingually deaf adults with English as a first language and on differences in access to perceptual information for normal-hearing versus the same deaf adults. The aim of Project I is to provide a detailed understanding of the relationship between how words are learned or used in terms of input channel - spoken, orthographic, finger spelled - and how words are processed. The hypothesis to be tested in terms of individual differences is that having more lexical experience in a communication channel facilitates word recognition via that same channel. The hypothesis will be investigated using behavioral and functional neuroanatomical (functional magnetic resonance imaging, fMRI) methods. Behavioral methods will include perceptual word identification, lexical decision, and subjective estimates of how words were learned. The fMRI task will be lipreading words by deaf adults, and analyses will focus on individual differences in magnitude and extent of activation. Behavioral and fMRI studies will expand on our previous research with the same methods and subject groups. The aim of Project II is to understand effects of perceiving words from phonetically impoverished (lipread) stimuli. The hypothesis to be tested is that phonetic information activates experientially derived word-form representations that are isomorphic with the chronically available perceptual (phonetic) information and not linguistically derived word-forms isomorphic with the phonemically distinct words in the language. This hypothesis predicts that spoken word-form representations based primarily on either optical (lipread by deaf adults) or acoustic (heard by hearing adults) signals during development will differ in the extent to which they approximate the phonemically different words in the language. Behavioral methods will include semantic priming and discrimination. fMRI experiments will investigate brain activation as a function of word-form similarity and phonotactics. The two projects will investigate fundamental scientific issues with direct clinical implications. For example, findings showing that how words are experienced affects how they are perceived would suggest that clinicians and educators of deaf children need to pay attention to the channel by which deaf children acquire language.