Vocal-auditory functions of the chimpanzee: consonant perception

The perception of consonants which were followed by the vowel [a] was studied in chimpanzees and humans, using a reaction time task in which reaction times for discrimination of syllables were taken as an index of similarity between consonants. Consonants used were 20 natural French consonants and six natural and synthetic Japanese stop consonants. Cluster and MDSCAL analyses of reaction times for discrimination of the French consonants suggested that the manner of articulation is the major determinant of the structure of the perception of consonants by the chimpanzees. Discrimination of stop consonants suggested that the major grouping in the chimpanzees was by voicing. The place of articulation from the lips to the velum was reproduced only in the perception of the synthetic unvoiced stop consonants in the two dimensional MDSCAL space. The phoneme-boundary effect (categorical perception) for the voicing and place-of-articulation features was also examined by a chimpanzee using synthetic [ga]-[ka] and [ba]-[da] continua, respectively. The chimpanzee showed enhanced discriminability at or near the phonetic boundaries between the velar voiced and unvoiced and also between the voiced bilabial and alveolar stops. These results suggest that the basic mechanism for the identification of consonants in chimpanzees is similar to that in humans, although chimpanzees are less accurate than humans in discrimination of consonants.