Speech perception in early infancy: Perceptual constancy for vowel categories

Abstract

The young infant discriminates a single token of /a/ from a single token of /i/ and can successfully ignore variations in the pitch contour of these vowels [Kuhl and Miller, J. Acoust. Soc. Am. 59, S54(A) (1976)], but demonstrations that an infant perceives an inherent similarity in a male's /a/ and a female's /a/ are lacking. Three infants, 512- to 6-months old, were tested in a task in which a head-turn response was reinforced with a visual stimulus in the presence of a speech sound from one category but not in the presence of a speech sound from a second category. The infants were trained with a single synthetically produced /a/ and /i/ whose formant frequencies and fundamental frequency were appropriate for a male voice (rise-fall pitch contour) and then tested with synthetic /a/ and /i/ tokens whose formant frequencies and fundamental frequencies were appropriate for female and child talkers, with both rising and rise-fall pitch contours. Generalization to novel tokens was often times immediate. The six-month old's behavior is suggestive of either an inherent, or easily learned, perceptual constancy for vowel categories when both the critical (formant frequencies) and noncritical (fundamental frequency, pitch contour) acoustic dimensions are randomly varied.