Abstract
When the onsets of three successive sound bursts mark two adjacent time intervals, the second time interval can be underestimated when it is physically longer than the first time interval by up to 100 ms. This illusion, time-shrinking, is very stable when the first time interval is 200 ms or shorter (Nakajima et al., 2004, Perception, 33). Time-shrinking had been considered a kind of perceptual assimilation to make the first and the second time interval more similar to each other. Here we investigated whether the underestimation of the second time interval was replaced by an overestimation if the physical difference between the neighboring time intervals was too large for the assimilation to take place; this was a typical situation in which a perceptual contrast could be expected. Three experiments to measure the overestimation/underestimation of the second time interval by the method of adjustment were conducted. The first time interval was varied from 40 to 280 ms, and such overestimations indeed took place when the first time interval was 80–280 ms. The overestimations were robust when the second time interval was longer than the first time interval by 240 ms or more, and the magnitude of the overestimation was larger than 100 ms in some conditions. Thus, a perceptual contrast to replace time-shrinking was established. An additional experiment indicated that this contrast did not affect the perception of the first time interval substantially: The contrast in the present conditions seemed unilateral.
Highlights
When the onsets of three successive sound bursts mark two neighboring time intervals, the second time interval can be underestimated when it is longer than the first time interval by up to 100 ms
It is widely observed that perceptual assimilation between objects gives way to contrast when the difference between these objects is increased, and that assimilation can be blocked if the area or the group to be assimilated is broken by a boundary, or by a temporal distance (Ikeda and Obonai, 1955)
The interaction between condition and tS duration was significant, F(8,32) = 4.614, p < 0.01, η2p = 0.536. This interaction should be related to the assimilation and contrast of tS to tP
Summary
When the onsets of three successive sound bursts mark two neighboring time intervals, the second time interval can be underestimated when it is longer than the first time interval by up to 100 ms This underestimation, i.e., time-shrinking, is very stable when the first time interval is 200 ms or shorter (Nakajima et al, 1991, 2004), and has been considered a kind of perceptual assimilation. A figure in which luminance is sufficiently higher than in the background can be distinguished clearly from the background in the visual modality This process is enhanced by contrast, which enlarges the perceptual difference in terms of lightness or color between the figure and the background, as well as by assimilation, which homogenizes the lightness or color within the figure and within the background (Koffka, 1935; Shapley and Reid, 1985). Assimilation and contrast were manipulated through modifying the temporal configuration of the sound bursts
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