Abstract
Sensory organs are thought to sample the environment rhythmically thereby providing periodic perceptual input. Whisking and sniffing are governed by oscillators which impose rhythms on the motor-control of sensory acquisition and consequently on sensory input. Saccadic eye movements are the main visual sampling mechanism in primates, and were suggested to constitute part of such a rhythmic exploration system. In this study we characterized saccadic rhythmicity, and examined whether it is consistent with autonomous oscillatory generator or with self-paced generation. Eye movements were tracked while observers were either free-viewing a movie or fixating a static stimulus. We inspected the temporal dynamics of exploratory and fixational saccades and quantified their first-order and high-order dependencies. Data were analyzed using methods derived from spike-train analysis, and tested against mathematical models and simulations. The findings show that saccade timings are explained by first-order dependencies, specifically by their refractory period. Saccade-timings are inconsistent with an autonomous pace-maker but are consistent with a “self-paced” generator, where each saccade is a link in a chain of neural processes that depend on the outcome of the saccade itself. We propose a mathematical model parsimoniously capturing various facets of saccade-timings, and suggest a possible neural mechanism producing the observed dynamics.
Highlights
Sensory organs are thought to sample the environment rhythmically thereby providing periodic perceptual input
Since saccades determine the visual inflow, explaining what governs their motor-control is vital for understanding the dynamics of vision
Not much is known about the temporal dynamics of saccades, and about the role of oscillations in saccade generation
Summary
Sensory organs are thought to sample the environment rhythmically thereby providing periodic perceptual input. The observed saccadic rhythmicity has led some to the speculate the existence of an oscillating generation process, possibly located in the motor cortex[27], which was thought to govern visual attention[26, 28,29,30]. According to this view, human saccades are modulated by the activity of autonomous oscillatory generators, to exploration behaviors in rodents. Human saccades are modulated by the activity of autonomous oscillatory generators, to exploration behaviors in rodents These generators supposedly act in parallel to the non-periodic environmental influences, generating the observed saccadic rhythmicity
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