Behavioral responses to harmonic complex tones with missing fundamental frequencies by chinchillas in the presence of low‐pass masking noise.

Abstract

The pitch associated with the missing fundamental (F0) is one of the principal psychological attributes of human pitch perception. Behavioral responses to missing F0 stimuli were measured in chinchillas using operant conditioning and stimulus generalization. Animals were trained to discriminate between harmonic complex tones having a 500‐Hz F0 and a 125‐Hz F0. When animals were tested with tone complexes having the same F0s, but where the F0s were missing, responses were similar to those obtained when the F0s were present, suggesting that missing F0 sounds were perceptually equivalent to F0 present sounds. In the presence of low‐pass masking noise, responses to F0 present and missing F0 stimuli were similar, suggesting that the percept was not due to the reinsertion of the F0 through cochlear nonlinearities. When the F0s of test stimuli were systematically varied, gradients in behavioral responses were observed, suggesting the existence of a psychological dimension related to F0. When the F0 and spectrum were varied independently, responses were related to the F0 rather than to spectral differences among test stimuli. The results indicate that chinchillas possess a pitchlike perception of the missing F0 that is unlikely to arise from cochlear distortion products. [Work supported by NIDCD R01 DC005596.]