Auditory stream segregation in Japanese monkeys

Japanese monkeys were examined to determine whether they perceptually segregate tone sequences. Monkeys were required to discriminate two sequences of tones (target sequences) differing in frequency contours. Distractor sequences were presented simultaneously with the target sequences. Monkeys could discriminate the sequences when the frequency ranges of the target and distractor sequences did not overlap, but they could not when the ranges overlapped. Subsequent probe tests confirmed that the discrimination depended on cues other than the local pitch of the component tones regardless of the presence of the distractor sequence. The results suggest that monkeys segregate tone sequences based on frequency proximity, and they perceive global characters of the segregated streams.