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An experimental study of fine-grain motion perception in the human visual system

Gravano, Salvatore

An experimental study of fine-grain motion perception in the human visual system Thumbnail


Salvatore Gravano


This thesis explores the characteristics of motion perception in the peripheral field of the human visual system as revealed by the fine-grain movement illusion, in which the sequential flashing of two spatially unresolved dot flashes results in the vivid perception of a single dot moving over a considerable distance.
A series of experiments is described in which consideration is given to the spatial and temporal dependence of the fine-grain movement illusion under different experimental conditions. Temporal response characteristics of the fine-grain movement illusion are determined, as a function of eccentricity, under conditions of photopic and scotopic adaptation. The temporal response characteristics of the illusion, which are determined using an objective measure of performance, are compared with temporal response characteristics obtained with a subjective measure of the illusion, in which subjects are required to rate the "strength" of the perceived illusion. Measurements are made of the minimum spatial separation required for two dot flashes to generate a fine-grain movement illusion. The minimum dot separation required for the fine-grain movement illusion is compared with the minimum dot separation required for spatial resolution; and the results are discussed in terms of possible motion- and form- detecting systems. Previous work has shown that fine-grain movement illusions may be made to interact with each other, so that two illusions generated sufficiently close together will, under appropriate conditions, destroy each other. Interaction thresholds, that is the minimum distance by which two illusions have to be separated so that they do not interfere in this way, are determined as a function of retinal eccentricity for different stimulus configurations. Measurements are made of the perceived extent of the illusion and its dependence on stimulus intensity and dot separation are determined. Two further experiments are described which consider extrapolations in classical apparent motion and these results are compared with the extents obtained for the fine-grain movement illusion.
Finally the implications of the experiments described in this thesis on visual motion perception and other areas of visual perception are considered.


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