Topographic organization is essential for pitch perception

Pitch is the perceptual attribute we associate most with melodies in music, patterns of bird songs, and the distinctions between speakers' voices. It plays a key role in the organization, segregation, and identification of sound sources in cluttered auditory scenes because it is derived from acoustic cues that closely reflect the material and geometric properties of resonating objects. Pitch has been the subject of intensive psychoacoustic studies for well over a century. In recent decades, physiological investigations in humans and animals have attempted to locate and understand the biological substrate underlying pitch perception at various levels of the auditory nervous system. However, despite all efforts, a deep understanding of the mechanisms that give rise to the pitch percept remains elusive. This uncertainty has generated passionate debates between the proponents of two very different theories of pitch, one based on the place or location of neural activation patterns, and the other on their temporal modulations. This state of affairs is now likely to change dramatically in favor of the place theories with the publication of results of intricately designed psychoacoustic experiments by Oxenham et al. (1) reported in this issue of PNAS.

There is universal agreement that pitch is basically a correlate of the periodicity of a sound waveform. The simplest such waveform is the pure tone (Fig. 1A); it is composed of a single sinusoid that gives rise to a pitch percept correlated with the frequency (or periodicity) of the sinusoid. A richer percept results when a complex periodic waveform is composed of several tones that are harmonically related, i.e., are integer multiples of a common fundamental frequency (Fig. 1B). Such a waveform evokes a salient and unified sense of pitch that we typically associate with the fundamental frequency regardless of the relative amplitudes of the harmonics, their dynamics, and …