DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS IN MACACA-MULATTA AND HUMANS

Distortion product otoacoustic emissions (DPOAEs) were compared in eig ht rhesus monkeys (Macaca mulatta) and eight normal hearing humans. DP OAEs were recorded in three conditions. In the first condition, DPOAEg rams were generated for monkeys and humans from approximately f(2) = 0 .5-20 kHz. Monkeys had larger amplitude DPOAEs at all frequencies exce pt around f(2) = 1 kHz. In the second condition, DPOAE amplitudes incr eased and then decreased as the separation between the primaries incre ased. These functions were similar in the two species except at the lo west frequencies assessed. In the third condition, the levels of the p rimaries were varied independently. Monkeys had steeper input/output ( I/O) functions than humans. The slopes of DPOAE I/O functions increase d with frequency in both species. When the levels of both primaries we re increased simultaneously, DPOAE I/O functions were well described b y power functions throughout the intensity range assessed (from thresh old to 65 dB SPL). Monkey I/O functions tended to be expansive power f unctions at all but the lowest frequencies, while human I/O functions tended to be compressive power functions except at the highest frequen cies assessed. Other differences in I/O functions at f(2) = 8 kHz may indicate species specific differences at high (for human) frequencies.