Audition, Speech Perception and Phonation of the Chimpanzee

Abstract

Audition, speech perception and phonation of the chimpanzee were studied to understand the course of evolution of human speech. (1) The chimpanzee showed W-shaped auditory sensitivity which is similar to that of monkeys and different from that of humans. The origin of the 4kHz dip was discussed. (2) The discrimination of vowels and consonants was studied using a reaction time task. The chimpanzee required long latenties in discriminating [i] from [u] and [e] from [o]. The relationship between the auditory sensitivity and the perception of vowels was discussed. The chimpanzee was reported to make use of the pitch and the 3rd and the 4th formants to normalize vowels. The chimpanzee showed categorical perception of the voicing and the place-of-articulation features of stop consonants. (3) The chimpanzee did not utter [i] and [e]. The small pharynx was suggested to be responsible for this repertoir of vowl-like sounds. The relationship between perception and production of vowels was discussed and it was suggested that the evolution of audition was matched to that of phonation. The difference in the vocal development between chimpanzees and humans was also discussed. (4) Auditory cortical neuronal responses of the Japanese monkey to conspecific coo sounds were reported. The neural lateralization of vocal reception in primates was discussed.