Hearing in the Monkey (Macaca) : Absolute and Differential Sensitivity

Monkeys were trained to make an observing response that was occasionally followed by a pure tone or by a change in the frequency or intensity of a continuously pulsed pure tone. A correct report of the stimulus or stimulus change was reinforced with food. Failure to report had no consequences, but an incorrect report produced a brief time‐out from the experiment. Thresholds were determined by both tracking and constant‐stimulus methods. The monkey's hearing is similar to man's at the lower frequencies (below 8 kHz) but extends to 45 kHz or an octave above the upper limit of human hearing. For tones below 8 kHz at 40 dB and 60 dB above threshold, the monkey's differential acuity for both frequency and intensity is slightly less than that of man. Differential sensitivity (ΔI and ΔF) for the monkey was found as high as 30 kHz at 40 dB above absolute threshold. [Research supported by PHS grants.]