Categorization and normalization of vowels by 3-year-old children

A two-alternative, forced-choice procedure was used in two experiments to test 3-year-old children’s categorization of natural vowel tokens produced by several talkers. An appropriate pointing response (right or left) was visually reinforced with one of two television displays. In Experiment 1, the stimuli were isolated tokens of /a/ and /i/ produced by a male adult, a female adult, a male child, and a female child. In Experiment 2, the stimuli were isolated tokens of /æ/ and /∧/ produced by the same talkers. In both experiments, 3-year-olds spontaneously generalized their pointing responses from the male adult vowel tokens to the corresponding vowels produced by the other talkers. Children reinforced for an arbitrary grouping of the two vowel categories persisted in categorizing on the basis of vowel quality. Results from both experiments demonstrate the presence of perceptual constancy for vowel tokens across talkers. In particular, the results from Experiment 2 provide evidence for normalization of isolated, quasi-steady-state vowel tokens because the formant values for tokens of /∧/ produced by the woman and the two children were closer to the formant frequencies of the male adult’s /æ/ than to the male adult’s /∧/.