EFFECTS OF ONSET ASYNCHRONY ON PITCH PERCEPTION - ADAPTATION OR GROUPING

A previous paper by Darwin and Ciocca [J. Acoust. Soc. Am. 91, 3381-3390 (1992)] showed that a slightly mistuned frequency component of a (target) harmonic complex produced smaller pitch shifts in the target if it started 160 ms or more before the other components than if all the components were simultaneous. Three experiments investigated whether this effect of onset asynchrony is due to peripheral adaptation to the leading portion of the mistuned component or to perceptual grouping. The first two experiments showed that the effect of asynchrony could be influenced by grouping mechanisms without changing the amount of adaptation produced by the leading portion of the mistuned component. In the first experiment, the effect of asynchrony was reduced by the presence of an additional (captor) complex which was harmonically related to the mistuned component and synchronous with just its leading portion. In experiment 2, the effect of asynchrony was increased by presenting a captor that was synchronous with the entire mistuned component. This capturing effect was independent of the harmonic relation between the captor and the mistuned component at 40-ms asynchrony; at 160 ms the effect of asynchrony increased further only if the captor and the mistuned component were harmonically related. In the third experiment, the expected amount of adaptation was increased (relative to that produced by a single sine precursor) by presenting several components that were close in frequency to the mistuned component and synchronous with its leading portion. This manipulation produced a larger reduction in pitch shift at short onset-time differences, but a smaller reduction at long onset time differences compared with the less intense sine precursor. The results of the three experiments are consistent with the original results being due mainly to perceptual grouping. Adaptation appears to be the dominant mechanism only at short onset asynchronies and when the leading portion of the mistuned component has been increased in intensity .