The Japanese journal of neuropsychology

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ArticleTitle	A study on developmental change in categorical perception of speech sounds
Language	J
AuthorList	Tatsuya Ogino¹⁾, Teruko Morooka²⁾, Akihito Takeuchi²⁾, Makio Oka²⁾, Yoko Ohtsuka²⁾
Affiliation	¹⁾Department of Children Studies, Faculty of Children Studies, Chugokugakuen University ²⁾Department of Child Neurology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences
Publication	Japanese Journal of Neuropsychology: 28 (4), 248-256, 2012
Received	Jun 6, 2011
Accepted	Oct 3, 2011
Abstract	To elucidate developmental change in the categorical perception of speech sounds, a categorical labeling task using/ka/-/ga/continua as stimuli was administered to 109 preschoolers (M 59; mean age 5 y 10 m), 30 second graders (M 16; mean age 8 y 1 m), and 21 adults (M 5; mean age 34 y 3 m). Models of labeling function were prepared in which voice onset times (VOT) of phoneme boundaries were determined arbitrarily. The boundary VOT of each model was one of 15 values ranging from -28 to 38 msec. Each subject was assigned to a particular model based on the smallest sum of the square of the difference between the proportion identified as /ga/ by the subject and that identified as /ga/ according to the model. The boundary VOT of the model was then considered to be the boundary of the subject. Fitness of the model was examined using simple regression analysis with actual measurements as the dependent variable and model measurements as the independent variable. Subjects with boundary VOT not greater than 24 msec were classified as the Adult type, while those with VOT greater than or equal to 30 msec were classified as the LongVOT type. Subjects whose labeling function did not significantly fit the model were classified as the Confusional type. Categorical Perception Index (CPI) was calculated as the second root of the sum of the square of the difference between the number of responses for/ga/ and the number of responses for /ka/. Both preschoolers and second graders showed significantly smaller CPI values and longer boundary VOT than adults. The LongVOT and Confusional groups consisted entirely of children; as subjects' age increased from preschool-age to second grade, the proportion of respondents classified as either of these types decreased, while the proportion classified as the Adult type increased. Though the categorical decisions made by children were more ambiguous than those made by adults, and the phoneme boundaries of children were different from those of adults, second graders were more likely to exhibit an Adult-type categorical perception profile than preschoolers were.
Keywords	perception of speech sounds, categorical perception, children, voice onset time (VOT), voiced and voiceless plosives