The perception of time-separation pitch by dolphins

Abstract

A dolphin was required to discriminate between rippled and nonrippled noise projected by an underwater transducer. Random noise was summed with its delayed replica to produce noise having ripples separated by 1/T Hz in the frequency domain, where T is the delay time. The dolphin detected the cos − rippled stimulus at a correct response level of at least 75% for delays between 15 and 500μs, and the cos + rippled stimulus for delays of 13 to 190 μs. The dolphin's sensitivity to rippled noise was measured by attenuating the delayed replica for different delays. The dolphin was most sensitive for a delay of 100 μs. Its sensitivity at 100 μs was 5 dB better for the cos + than the cos − stimuli. The broadband cos + noise was also filtered in different 1/3 octave bands to determined if the animal's sensitivity to rippled noise was a function of the center frequency of the noise. The dolphin's performance was relatively constant as a function of center frequency. The overall results suggest that dolphins may be able to perceive time-separation pitch.