Repetition ‘‘pitch’’ in chinchillas

Abstract

Repetition pitches are evoked in human listeners by rippled noises. Infinitely iterated rippled noise (IIRN) is generated when wideband noise is delayed, attenuated, and added to the original wideband noise through positive (+) or negative (−) feedback. In human listeners, the pitch of IIRN(+) is matched to the reciprocal of the delay, whereas the pitch of IIRN(−) is an octave lower. A stimulus generalization paradigm was used to characterize IIRN repetition pitch in chinchillas. Chinchillas were trained to discriminate IIRN(+) with a 4-ms delay from IIRN(+) with a 2-ms delay. In the generalization task, chinchillas were tested with IIRN(+) having delays between 2–4 ms. The pitches evoked by these IIRNs ranged from 500–250 Hz. The delayed noise attenuation for all IIRNs was fixed at −1 dB. A systematic gradient in behavioral response occurred along the dimension of delay for each animal tested, suggesting that a perceptual dimension of pitch exists. Responses to IIRN(−) evoking pitches between 500–250 Hz (delays of 1–2 ms) were also measured. Responses to IIRN(−) were more variable among animals, suggesting that other perceptual cues such as timbre differences may be stronger than the pitch cues. [Work supported by NIDCD R01 DC005596.]