The perception of frequency peaks and troughs in wide frequency modulations. III. Complex carriers.

In widely frequency-modulated (FM) sine tones, local frequency maxima are perceived more accurately than local frequency minima [L. Demany and K. I. McAnally, J. Acoust. Soc. Am. 96, 706-715 (1994); L. Demany and S. Clément, J. Acoust. Soc. Am. 97, 2454-2459 (1995)]. The aim of the present work was to determine if a similar perceptual asymmetry exists for nonsinusoidal FM carriers. Within each stimulus, the logarithm of instantaneous frequency followed one cycle of a (2.5- or 5-Hz) cosine function, starting at phase pi in the "peak" condition and phase 0 in the "trough" condition. In each condition, subjects had to detect shifts in the frequency apex occurring at the temporal center of the stimuli. In experiment 1, the FM functions were imposed on complex tones consisting of a series of consecutive harmonics. Some of the stimuli were bandpass filtered in a 1-oct window with fixed edges. The measured thresholds were about four times lower in the peak condition than in the trough condition, which suggests that the asymmetry previously observed for "spectral" pitches also exists for "virtual" pitches. In experiment 2, the FM carriers were Shepard tones. With such carriers, the standard peak and trough stimuli could be made identical at both the apex and the end points. In spite of these local identities, the results were similar to those of experiment 1, which suggests that the perceptual asymmetry is not determined by local differences between the stimuli and is instead a genuine "motion" effect.(ABSTRACT TRUNCATED AT 250 WORDS)