Contributions of miniature eye movements to visual perception.

摘要

During periods of fixation, slow drifts and microscopic saccades continually perturb the projection of the visual scene onto the retina. This dissertation describes three studies that investigated the contributions of these small eye movements to visual perception.;According to a long-standing hypothesis, the primary role of microsaccades is to prevent the visual world from fading during fixation. However, it is still debated whether visual fading elicits microsaccades. The psychophysical experiments described in this thesis found no causal relationship between microsaccades and visual fading. In contrast, the new experimental findings support the view that microsaccades are coordinated by the visual system to keep the preferred retinal location on the attended stimulus during fixation.;Analysis of visual discrimination in the presence and in the absence of the retinal image motion caused by fixational eye movements has shown that the luminance modulations resulting from fixational instability improve discrimination of visual detail. New modeling results, obtained by simulating the responses of retinal ganglion cells in these experiments, reveal that fixational eye movements have a profound influence on synchronous activity. These and other recent results suggest that the synchronization of retinal activity induced by fixational eye movements is a key component of the neural mechanisms that promote perception of spatial detail.;The incessant retinal motion introduced by ocular drift constitutes a problem for visual stability; how does the brain know if the motion of an object on the retina is caused by fixational instability or external motion? Long debated is whether an extraretinal signal helps identify and discard the retinal motion due to eye movements, and thus improves perception of object motion. A third new study shows that, in darkness or normal illumination, the visual system achieves perception of a stable world during fixation by relying on the spatiotemporal pattern of stimuli on the retina.;The research described in this dissertation challenges some of the mainstream approaches in the field, by showing that, (a) visual fading does not elevate the rate of microsaccades, (b) luminance modulations due to ocular drift enhance visual detail, and (e) retinal motion introduced by fixational drifts is cancelled visually.