A Neural Marker of the Start-Gun in Interval Timing: Onset N1P2
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Although the neural markers of interval timing have been widely studied, the events that determine the onset and offset of an interval have only recently started to gain attention. In the present study, I compare the predictions of the perceptual (preonset and start-gun) and decisional bias hypotheses with respect to onset N1P2 amplitude, the point of subjective equality (PSE) and delta/theta activity. The onsets of the comparison intervals (CIs) were manipulated to begin earlier, later, or on-time with regard to a standard interval (SI). Results supported the start-gun account by demonstrating an increase in the N1P2 amplitude and delta power in the "early" and "late" onset conditions due to temporal mismatch. Delayed or premature initiation of timing with respect to the predicted temporal point were associated with rightward and leftward shifts in the PSEs of the "early" and "late" onset conditions, respectively. In addition to the observed increase in temporal prediction-related delta activity in the "early" and "late" onset conditions, higher theta power in the "early" onset suggested an additional neural response for unexpected events that might be linked to response caution. Moreover, the ramping activity during the CIs, namely the contingent negative variation (CNV), showed a decision-related attenuation toward the end of an interval in the "late" onset. The latter finding was supported by the changes in offset N1P2 amplitude. The present study contributes to the interval-timing literature by presenting support in favor of the hypothesis that the onset N1P2 is a neural marker for the initiation of timing.