Multiple pitch mechanisms revealed by effects of inharmonicity on pitch perception

Abstract

Pitch is generally defined as the percept corresponding to a sound’s fundamental frequency (F0). However, there is surprisingly little evidence for the importance of F0-specific mechanisms in pitch perception. To investigate the extent to which pitch perception involves estimating F0, we conducted a battery of pitch-related music and speech tasks using harmonic and inharmonic stimuli, the rationale being that inharmonic stimuli lack a clear F0 and should impair F0-dependent mechanisms. Inharmonic speech was generated with a variant of STRAIGHT analysis/synthesis. We found no difference in performance between harmonic and inharmonic stimuli for basic pitch discrimination, melodic contour discrimination, and speech contour discrimination, but substantial inharmonicity-induced deficits for sour-note detection, interval recognition and discrimination, melody recognition, and voice recognition. Collectively, the results indicate that F0 estimation is not necessary to extract pitch contours in speech or music, but does appear critical for accurate interval perception, and for representing voices. These findings suggest that two or three distinct mechanisms may underlie what has conventionally been couched as pitch perception: one which tracks shifts in fine spectral patterns independent of F0, another that estimates F0 for determining precise interval relationships between notes, and perhaps another associated with voice qualities.