'Time-shrinking perception' in the visual system: a psychophysical and high-density ERP study.

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'Time-shrinking perception (TSP)' is a unique perceptual phenomenon in which the duration of two successive intervals (T1 and T2) marked by three auditory stimuli is perceived as equal even when they are physically different. This phenomenon provides a link between time and working memory; however, previous studies have mainly been performed on the auditory modality but not the visual modality. To clarify the neural mechanism of visual TSP, we performed a psychophysical experiment and recorded event-related potentials (ERPs) under different T1/T2 combinations. Three successive black/white sinusoidal gratings (30ms duration) were presented to the participants. In the psychophysical experiment, either T1 or T2 was varied from 240 to 560ms in 40-ms steps, while T2 or T1 was fixed at 400ms. Participants judged whether T1 and T2 were equal or not by pressing a button. ERPs were recorded from 128 scalp electrodes, while T1 was varied from 240, 320, and 400ms with the 400ms T2 duration, and vice versa. Behavioral data showed asymmetrical assimilation: When -80ms≤(T1-T2)≤+120ms, TSP was observed in the T1-varied condition. When -120ms≤(T1-T2)≤+80ms, it was also observed in the T2-varied condition. These asymmetric time ranges in vision were different from those in the auditory modality. ERP data showed that contingent negative variation (CNV) appeared in the fronto-central region at around 300-500ms during T2 presentation in the T1<T2 condition. In the /240/400/ pattern, the CNV amplitude was decreased at around 350ms. In contrast, P3 appeared at the parietal region about 450-650ms after T2 in the T1>T2 condition. In the /400/240/ pattern, P3 amplitude was greater than those of other temporal patterns. These neural responses corresponded to participants' perception that T1 and T2 were not equal. The neural responses in the fronto-central region were involved with endogenous temporal attention for discrimination. Moreover, neural responses in the parietal region were engaged in exogenous temporal attention. Therefore, fronto-parietal neural responses underlie temporal perception in vision.