Abstract
Background: Microsaccades are known to be inhibited in response to perceptual events. We have recently reported (Bonneh et al, VSS 2012) that the latency of the release from inhibition depends systematically on the history of preceding events. Here we explore both the onsets and offsets of this inhibition using various visual and auditory stimuli. Method: During fixation observers viewed and silently counted all items in sequences of 100 randomly ordered stimuli of two types, presented at 1 Hz repetition rate. These included small patches of contrast (high/low), color (red/blue), spatial position (up/down), and audio-visual stimuli (beep/circle). Eye-tracking data were used to compute the average latencies of the first microsaccade (if present) in two time windows: early (0-300 ms) corresponding to the onset of inhibition, and late (e.g. 200-700 ms, varied across conditions) corresponding to inhibition release. Results: In all conditions, repetition (e.g. red after a sequence of reds) delayed the onset of inhibition and shortened the latency of its release, while change (e.g. red after a sequence of blues) shortened the onset of inhibition (as early as 100ms) and increased the latency of its release. The magnitude of these effects changed systematically with the number of preceding items (up to 4-5), 5-10ms per item, with 20ms per item for the total inhibitory duration. We verified the significance of the effects in comparison to a random shuffle (Monte-Carlo method). Conclusion: Microsaccades are inhibited in time intervals that depend on the relation between the current event and the pattern of preceding events. We describe this dependency in terms of a simple quantitative model that computes the likelihood ("prediction") of future events based on the recent past, and assumes faster and longer inhibition for events with higher prediction error. The current measure of implicit perceptual predictions could be applied to non-communicating individuals.
Meeting abstract presented at VSS 2013