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Visual language discrimination Weikum, Whitney Marie

Abstract

Recognizing and learning one’s native language requires knowledge of the phonetic and rhythmical characteristics of the language. Few studies address the rich source of language information available in a speaker’s face. Solely visual speech permits language discrimination in adults (Soto-Faraco et al., 2007). This thesis tested infants and adults on their ability to use only information available in a speaker’s face to discriminate rhythmically dissimilar languages. Monolingual English infants discriminated French and English using only visual speech at 4 and 6 months old, but failed this task at 8 months old. To test the role of language experience, bilingual (English/French) 6 and 8-month-old infants were tested and successfully discriminated the languages. An optimal period for sensitivity to visual language information necessary for discriminating languages may exist in early life. To confirm an optimal period, adults who had acquired English as a second language were tested. If English was learned before age 6 years, adults discriminated English and French, but if English was learned after age 6, adults performed at chance. Experience with visual speech information in early childhood influences adult performance. To better understand the developmental trajectory of visual language discrimination, visual correlates of phonetic segments and rhythmical information were examined. When clips were manipulated to remove rhythmical information, infants used segmental visual phonetic cues to discriminate languages at 4, but not 8 months old. This suggests that a decline in non-native visual phonetic discrimination (similar to the decline seen for non-native auditory phonetic information; Werker & Tees, 1984), may be impairing language discrimination at 8 months. Infants as young as newborn use rhythmical auditory information to discriminate languages presented forward, but not backward (Mehler et al., 1988). This thesis showed that both 4 and 8-month-old infants could discriminate French from English when shown reversed language clips. Unlike auditory speech, reversed visual speech must conserve cues that permit language discrimination. Infants’ abilities to distinguish languages using visual speech parallel auditory speech findings, but also diverge to highlight unique characteristics of visual speech. Together, these studies further enrich our understanding of how infants come to recognize and learn their native language(s).

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Attribution-NonCommercial-NoDerivatives 4.0 International

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