Categorical Rhythm Perception as a Result of Unilateral Assimilation in Time-Shrinking

Abstract

In previous studies, we established an illusion of time perception that we called time-shrinking: an empty time interval, immediately preceded by a slightly shorter time interval, is underestimated. In the first experiment of the present study, we examined the perceived duration not only of the second interval (t2), but also of the first interval (tl). The empty time intervals tl and t2, making a total duration of 90,180, 360, or 720 ms, were presented such that the time ratio between them changed systematically. The points of subjective equality of tl and t2 were established by the method of adjustment. In the patterns typically susceptible to timeshrinking, that is, in which t2 was underestimated, tl was perceived almost vertically. In the second experiment, listeners had to bisect an empty duration of 180 ms, marked by sound bursts. The bisecting sound marker was positioned closer to the initial marker than to the final one. Thus, tl had to be shorter than t2 in order for a regular pattern to be perceived. In the third experiment, just-noticeable forward and backward displacements of the middle sound marker were measured by a transformed updown method. The prediction that the interval of uncertainty was closer to the initial than to the final sound marker was confirmed. The three experiments demonstrated the existence of unilateral temporal assimilation, and it is argued that this perceptual mechanism causes a category of 1:1 rhythms, despite a considerable change in temporal ratio between two contiguous time intervals.

Electrophysiological Evidence of Auditory Temporal Perception Related to the Assimilation Between Two Neighboring Time Intervals

“…We demonstrated that ERP components related to temporal perception could be extracted by contrasting the brain activations in the judgment condition and in the no-judgment condition. Behavioral results showed a clear assimilation: participants judged the two neighboring time intervals as equal when -40 ≤ (T1-T2) ≤ +40 ms. One of our previous studies has confirmed that the range of temporal assimilation was clearly beyond the range indicated by the just noticeable differences (JNDs) of short time intervals (Sasaki et al, 1998). These data agree with the present behavioral data, in which the 'same' responses in a certain range around zero millisecond should have been caused by assimilation.…”

“…Following these findings, the above attenuation of the SNCt activity can be explained by the economic information processing in the brain. The attenuation of SNCt observed in Experiment 2 in conditions where neighboring time intervals are mostly perceived as equal seems to have been caused by the occurrence of the unilateral or bilateral assimilation (Sasaki et al, 1998;Miyauchi & Nakajima, 2005;2007;Nakajima, et al, 2004;ten Hoopen et al, 2006). According to our psychophysical model of unilateral temporal assimilation (Nakajima, et al, 2004), the perceived difference between T1 and T2 should be reduced by cutting the processing time for T2 after the offset of the 3rd marker.…”

“…It is argued that judgments at subsecond timing lead to various types of perceptual distortions -illusions -in several modalities. So far, we have found a couple of phenomena related to auditory temporal perception in short time intervals by means of psychophysical measurements (Nakajima, ten Hoopen, & van der Wilk, 1991;Sasaki, Nakajima, & ten Hoopen, 1998;Miyauchi & Nakajima, 2005, 2007ten Hoopen, Sasaki, Nakajima, Remijn, Massier, Rhebergen, & Holleman, 2006). One is so-called 'temporal assimilation,' in which physically different, short time intervals are perceived as (almost) equal to each other when they neighbor each other (Nakajima, et al, 1991;Miyauchi & Nakajima, 2005;2007).…”

Bilateral Assimilation of Two Neighboring Empty Time Intervals

“…They assured that time-shrinking, as assimilation, was asymmetric in time and unilateral, because the illusion appeared only when t2 was longer than t1, and only the perception of t2 was affected. Sasaki et al (1998) measured the PSEs of two neighboring empty time intervals and confirmed the idea that time-shrinking was unilateral assimilation. A closer look at their data shows that a different assimilation also seems to have appeared outside of the range in which the unilateral assimilation took place.…”

“…It is often thought that these assimilations take place when a single continuous dimension is mapped into perceptual categories (e.g., rhythmic and phonemic categories) and does not occur directly with regard to the dimension constituting the stimulus pattern. A study of time perception (Sasaki, Nakajima, & ten Hoopen, 1998), however, suggested that assimilation in points of subjective equality (PSEs) of duration appeared when two empty time intervals were adjacent. This may indicate that assimilation takes place in the dimension of time itself.…”