Abstract
Background: Temporal regularities in the environment and especially rhythmic stimuli are known to facilitate the response to events that appear temporally in-phase with these regularities, presumably reflecting unintentional and implicit predictions about the time of upcoming events. However, not much is known about the underlying mechanisms, the buildup process, and the level of automaticity or dependence on behavioral responses. Here we used the time course of microsaccades, which are small involuntary saccades occurring during fixation, as well as eye-blinks, to explore the buildup of temporal anticipation and its underlying mechanisms. Method: In a set of experiments, observers (n=7) passively viewed and silently counted sequences of 90 high-contrast Gabor patches, briefly flashed in around 1 Hz repetition rate at fixation. To explore the buildup of temporal anticipation, we used two randomly interleaved inter-stimulus onset intervals that differed by 100, 200, and 500 ms in separate conditions. Results: We first found that the microsaccade and eye-blink rate modulations were entrained by a fixed stimulus repetition rate, with anticipatory inhibition that reached its maxima around stimulus onset. When two intervals were mixed, we found that repetition of the same interval shortened the microsaccade inhibition period for the corresponding stimulus, while a change of interval increased it, with a magnitude that changed systematically with the number of recent (4-5) preceding events. These results were obtained for all interval pairs, including a small interval difference of 100ms which observers did not notice, demonstrating the high precision of the anticipation mechanism and its independence of perceptual awareness. Conclusion: We interpret the results as reflecting an ongoing process that computes implicit temporal predictions based on the recent past. Rhythmic stimuli induce a gradual buildup and tuning of this predictive mechanism resulting in a proportionally faster processing and shorter microsaccade inhibition for in-phase stimuli.
Meeting abstract presented at VSS 2016