Phylogeny and Outogeny of Speech Perception

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The following five points were investigated : 1) The categorical perception of stop consonants in the chimpanzee, 2) Procedures to study speech perception in human infants, 3) The ability of vocal tract normalization in the Japanese monkey, chimpanzee and human, 4) Ear advantages in the perception of species specific vocal sounds in the Japanese monkey and chimpanzee, and 5) Imitation in the chimpanzee.The followings are the results : 1) The categorical perception of stop consonants was studied using [ga]-[ka] and [ba]-[da] continua in the chimpazee. The subject showed the phoneme boundary effect (categorical perception) in discrimination of voicing and place-of-articulation features. 2) Both non-nuturi-tive sucking and head turning procedures were examined. It was concluded that the latter method was more effective than the former. 3) The ability of vocal tract normalization was examined using [o]-[a] continua with the low and high fundamental frequency. Both the Japanese monkey and chimpanzee showed a shift in the boundary between [o] and [a] depending on the frequency of the pitch, suggesting that they have the ability of vocal tract normalization. 4) Ear advantages were examined using species specific vocal sounds in the Japanese monkey and chimpanzee. Early high and late high coo calls of the Japanese monkey and grunts, whimpers and squeaks were discriminated by the left or the right ear separately. No stable ear advantages were obtained in the both species. 5) It was not easy for the chimpanzee to imitate acts of a model which were directed to invisible body parts. However, when acts were directed to the external environment or when the manipulation of objects was involved, imitation became easier. Molding and operant conditioning were necessary for the ocurrance of imitation in the chimpanzee.