Whether the mechanisms giving rise to pitch reflect spectral or temporal processing has long been debated. Generally, sounds having strong harmonic structures in their spectra have strong periodicities in their temporal structures. We found that when a wideband harmonic tone complex is passed through a noise vocoder, the resulting sound can have a harmonic structure with a large peak-to-valley ratio, but with little or no periodicity in the temporal structure. To test the role of harmonic structure in pitch perception for a non-human mammal, we measured behavioral responses to noise-vocoded tone complexes in chinchillas using a stimulus generalization paradigm. Animals discriminated either a harmonic tone complex or an iterated rippled noise from a 1-channel vocoded version of the tone complex. When tested with vocoded versions generated with 8, 16, 32, 64 and 128 channels, responses were similar to those of the 1-channel version. Behavioral responses could not be accounted for based on harmonic peak-to-valley ratio as the acoustic cue, but could be accounted for based on temporal properties of the autocorrelation functions such as periodicity strength or the height of the first peak. The results suggest that pitch perception does not arise through spectral processing in non-human mammals, but rather through temporal processing. The conclusion that spectral processing contributes little to pitch in non-human mammals may reflect broader cochlear tuning than that described in humans.

Mechanisms giving rise to pitch reflect spectral or temporal processing is still equivocal, because sounds having strong harmonic structures also have strong temporal structures. When a harmonic tone complex is passed through a noise vocoder, the resulting sound can have a harmonic structure with large peak-to-valley ratios, but little or no temporal structure. To test the role of harmonic structure in mammals, we measured behavioral responses to vocoded tone complexes in chinchillas using a stimulus generalization paradigm. Animals discriminated a harmonic tone complex from a one-channel vocoded version of the complex. When tested with vocoded versions generated with 8–128 channels, animals generalized to the one-channel version and showed no gradient in their behavioral responses. This suggests that spectral structure was not the cue for the behavioral response. To further test this, chinchillas discriminated an iterated rippled noise from the one-channel vocoded tone complex. When tested using vocoded tone complexes having harmonic peak-to-valley ratios that were larger than or similar to the rippled noise, animals again generalized to the 1-channel version rather than the to rippled noise. The results suggest that mammalian “pitch” attributes arise through temporal, not spectral, processing mechanisms. [Work supported by NIDCD R01 DC005596.]