UBC Theses and Dissertations
Visual influences on speech perception in infancy Danielson, Donald Kyle
The perception of speech involves the integration of both heard and seen signals. Increasing evidence indicates that even young infants are sensitive to the correspondence between these sensory signals, and adding visual information to the auditory speech signal can change infants’ perception. Nonetheless, important questions remain regarding the nature of and limits to early audiovisual speech perception. In the first set of experiments in this thesis, I use a novel eyetracking method to investigate whether English-learning six-, nine-, and 11-month-olds detect content correspondence in auditory and visual information when perceiving non-native speech. Six- and nine-month-olds, prior to and in the midst of perceptual attunement, switch their face-scanning patterns in response to incongruent speech, evidence that infants at these ages detect audiovisual incongruence even in non-native speech. I then probe whether this familiarization, to congruent or incongruent speech, affects infants’ perception such that auditory-only phonetic discrimination of the non-native sounds is changed. I find that familiarization to incongruent speech changes—but does not entirely disrupt—six-month-olds’ auditory discrimination. Nine- and 11-month-olds, in the midst and at the end of perceptual attunement, do not discriminate the non-native sounds regardless of familiarization condition. In the second set of experiments, I test how temporal information and phonetic content information may both contribute to an infant’s use of auditory and visual information in the perception of speech. I familiarize six-month-olds to audiovisual Hindi speech sounds in which the auditory and visual signals of the speech are incongruent in content and, in two conditions, are also temporally asynchronous. I hypothesize that, when presented with temporally synchronous, incongruent stimuli, infants rely on either the auditory or the visual information in the signal and use that information to categorize the speech event. Further, I predict that the addition of a temporal offset to this incongruent speech changes infants’ use of the auditory and visual information. Although the main results of this latter study are inconclusive, post-hoc analyses suggest that when visual information is presented first or synchronously with auditory information, as is the case in the environment, infants exhibit a moderate matching preference for auditory information at test.
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