Spatiotemporal brain dynamics of auditory temporal assimilation

Time is a fundamental dimension, but millisecond-level judgments sometimes lead to perceptual illusions. We previously introduced a “time-shrinking illusion” using a psychological paradigm that induces auditory temporal assimilation (ATA). In ATA, the duration of two successive intervals (T1 and T2), marked by three auditory stimuli, can be perceived as equal when they are not. Here, we investigate the spatiotemporal profile of human temporal judgments using magnetoencephalography (MEG). Behavioural results showed typical ATA: participants judged T1 and T2 as equal when T2 − T1 ≤ +80 ms. MEG source-localisation analysis demonstrated that regional activity differences between judgment and no-judgment conditions emerged in the temporoparietal junction (TPJ) during T2. This observation in the TPJ may indicate its involvement in the encoding process when T1 ≠ T2. Activation in the inferior frontal gyrus (IFG) was enhanced irrespective of the stimulus patterns when participants engaged in temporal judgment. Furthermore, just after the final marker, activity in the IFG was enhanced specifically for the time-shrinking pattern. This indicates that activity in the IFG is also related to the illusory perception of time-interval equality. Based on these observations, we propose neural signatures for judgments of temporal equality in the human brain.


Supplementary Audio
Audio patterns that do or do not cause auditory temporal assimilation (ATA). Readers should listen to Supplementary Audio to appreciate the phenomenon and the behavioural and neurophysiological results. Supplementary Audio 1-3 are for demonstration purposes and 4-6 are the stimuli used in the Experiment. Confirm for yourself that the temporal relationship is only reversed in time between Supplementary Audio 1 and 3, yet 1 and 3 produce different perceptual effects, and that the same T2 interval of 200 ms apparently sounds different between Supplementary Audio 4 and 6. Please note that ATA occurs not only in auditory but also in visual 4, 5 and tactile 6 modalities.
Therefore, ATA is generally involved in interval judgments for similarly-organised stimuli and unlikely to be related to sensory temporal integration.
Perception 33, 1061-1079 (2004  The blue lines represent the time-series data for the equal responses (n = 6 for T1<2 (I) and n = 8 for T1>2 (III)) regional activity, and the red lines denote those for the unequal responses.
Colour-matched transparent areas represent the SEs of the averaged activations. In the judgment condition, participants were required to judge whether the T1 and T2 durations were equal by pressing one of two buttons. We analysed these responses based on the data sets of the judgment condition in the right hemisphere. We split the judgment trials of T1<2 and T1>2 based on participants' equal (EQ) and unequal (UE) responses. The data analysis was based on the same procedure used for the left hemisphere and right hemisphere comparison ( Fig. 2) and the judgment and no-judgment comparison (Fig. 3). First, we identified the analysable dataset, because some participants' data contained extremely small numbers of equal or unequal responses and were statistically not feasible to analyse. We then set the threshold to be at least 16 trials, because the MNE suit software requires this number to create a stable sensor covariance matrix. more than 82% of the trials. The behavioural activity associated with the EQ/UE judgment differed between the T1<2 and T1>2 conditions. This implies that different cognitive processing occurred in the two conditions. In general, sufficient numbers of trials and participants are necessary to report robust evidence. Thus, other approaches are required to confirm that these differential behaviours are indeed associated with the illusion.    Figure 5A and the one-way ANOVA for the right-IFG values that are plotted in Figure 5B. For the two-way ANOVA, the major factors were Stimulus Pattern (3 levels: T1<2, T1=2, T1>2) and Condition (2 levels: Judgment and No Judgment). The one-way ANOVA looked at Stimulus Pattern (3 levels: T1<2, T1=2, T1>2). In the right TPJ, we observed a significant main effect of Stimulus (p < 0.01, ** ) and a marginally non-significant main effect of Condition (p = 0.054, + ). Multiple comparisons among the stimulus factors revealed that the integrated amplitude within 70 ms after M2 was significantly larger for the T1<2 pattern than for the T1=2 (p < 0.01) and T1>2 (p = 0.035) stimulus patterns. In the right IFG, the main effect of stimulus pattern was significant (F2,32 = 4.29, p < 0.03, η 2 p = 0.21). The integrated regional activity amplitudes for the T1<2 pattern were significantly larger than those for the T1=2 (p = 0.053) and T1>2 (p = 0.029) patterns.
Hironaga et al. 14 The individual peak amplitudes and latencies within the 101-191-ms time window that are plotted in Figures 5B-(b) and 5B-(c) are shown.