Time stretching: Illusory lengthening of filled auditory durations

The second of two consecutively presented sounds may be perceived as being longer than if that sound had been presented in isolation. We performed five experiments using heterophonic patterns in which a sine tone was preceded by a frequency-band noise. We observed significant overestimations of sine-tone duration, the size of which depended on intensity and frequency differences between the band noise and the sine tone (Experiments 1 and 2). Band noises that were considerably shorter than the sine tone still caused significant overestimations (Experiment 3). A short silent gap between the band noise and the sine tone strongly reduced the amount of overestimation (Experiment 4). Both frozen and nonfrozen band noises yielded overestimations (Experiment 5). Our explanation for the overestimation is that the onset of the sine tone is blurred by the band noise and that such a blurred onset is restored at the level of perceptual organization following rules of a simple auditory grammar. This restoration takes mental processing time, which adds to the perceived duration of the sine tone. We call this illusion time stretching and discuss the notion that subsequent temporal assimilation and/or contrast effects can dilate or compress the amount of stretching.