Perceptual fusion and fragmentation of complex tones made inharmonic by applying different degrees of frequency shift and spectral stretch

Global pitch depends on harmonic relations between components, but the perc eptual coherence of a complex tone cannot be explained in the same way. Ins tead, it has been proposed that the auditory system responds to a common pa ttern of equal spacing between components, but is only sensitive to deviati ons from this pattern over a limited range [Roberts and Brunstrom, J. Acous t. Soc. Am. 104, 2326-2338 (1998)]. This hypothesis predicts that spectral fusion will be largely unaffected either by frequency shifting a harmonic s timulus (because equal spacing is preserved), or by small degrees of spectr al stretch (because significant deviations from equal spacing only cumulate over large spectral distances). Complex tones were either shifted by 0%-50 % of F0 (200 HZ +/- 10%) or stretched by 0%-12% of F0 (100 Hz +/- 10%). Sub jects heard a complex followed by a pure tone in a continuous loop. One of the components 2-11. was mistuned by +/-4%, and subjects adjusted the pure tone to match its pitch. Broadly consistent with our hypothesis, frequency shifts had relatively little effect on hit rates and only large degrees of stretch reduced them substantially. The implications for simultaneous group ing are explored with reference to an autocorrelation model of auditory pro cessing. (C) 2001 Acoustical Society of America.