Separate mechanisms govern the selection of spectral components for perceptual fusion and for the computation of global pitch.

The perceptual fusion of harmonics is often assumed to result from the operation of a template mechanism that is also responsible for computing global pitch. This dual-role hypothesis was tested using frequency-shifted complexes. These sounds are inharmonic, but preserve a regular pattern of equal component spacing. The stimuli had a nominal fundamental (F0) frequency of 200 Hz (+/- 20%), and were frequency shifted either by 25.0% or 37.5% of F0. Three consecutive components (6-8) were removed and replaced with a sinusoidal probe, located at one of a set of positions spanning the gap. On any trial, subjects heard a complex tone followed by an adjustable pure tone in a continuous loop. Subjects were well able to match the pitch of the probe unless it corresponded with a position predicted by the spectral pattern of the complex. Peripheral factors could not account for this finding. In contrast, hit rates were not depressed for probes positioned at integer multiples of the F0(s) corresponding to the global pitch(es) of the complex, predicted from previous data [Patterson, J. Acoust. Soc. Am. 53, 1565-1572 (1973)]. These findings suggest that separate central mechanisms are responsible for computing global pitch and for the perceptual grouping of partials.