Perception of the Missing Fundamental by Chinchillas in the Presence of Low-Pass Masking Noise

The pitch of the missing fundamental (F0) is one of the principal psychological attributes of human pitch perception. Behavioral responses to harmonic tone complexes having missing F0s were measured in chinchillas using operant conditioning and stimulus generalization. Animals were trained to discriminate between tone complexes 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. Behavioral responses to F0 present and missing F0 stimuli were similar in the presence of low-pass masking noise, suggesting that the perception was not due to the reinsertion of the F0 through cochlear nonlinearities. Gradients in behavioral responses were observed when the F0s of test complexes were systematically varied, suggesting the existence of a psychological dimension related to F0. Behavioral responses were related to the F0 rather than to spectral differences among test stimuli when the F0 and spectrum were varied independently. The results indicate that chinchillas possess a pitch-like perception of the missing F0 that is unlikely to arise from cochlear distortion products.