Influence of tone duration and intertone interval on the discrimination of frequency contours in a macaque monkey.

Behavioral studies have shown that non-human primates can categorically discriminate descending from ascending frequency steps in sequences of pure tones. Here we show that the performance of a long-tail macaque remains stable in such a task when the silent interval between the tones of a frequency step is varied between 0 and 1100 ms. Our finding suggests that: (1) some monkeys can keep frequency-specific information in their short-term memory for periods >1s, which can be used to make categorical decisions on the direction of frequency steps, and that (2) their ability to categorize the direction of frequency steps may be more similar to humans than previously assumed.