Effect of signal component phase on asynchrony discrimination

The ability of listeners to detect the temporal asynchrony of a single harmonic in complex sounds was measured. The listeners discriminated an asynchronous complex from one in which all harmonics were synchronous (standard). The asynchrony was created either at the onset or offset of the complex. In the asynchronous complex, one component either began or ended after all other components in the complex, or it began or ended prior to all other components in the complex. The phase of the signal component was systematically varied in the range from 0 degrees to 180 degrees. All nonsignal components had the same sine phase. The results show that detecting the asynchrony at the onset is superior when all components are in sine phase. Altering the phase of the signal component increased thresholds by as much as a factor of 50, with the largest thresholds obtained when the signal component was inverted in phase. For offset conditions, the phase of the signal component had a much smaller and less consistent effect. Some of the observed effects of phase on the asynchrony thresholds can be understood by considering the response of the Roex filter [Patterson et al., J. Acoust. Soc. Am. 72, 1788-1803 (1982)] centered at the signal frequency.