Visual discrimination as a function of stimulus size, shape, and edge-gradient
Fox, Wyatt Ray
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The basic response of the visual mechanism is the discrimination of changes in luminous intensity in the visual world. This discrimination consists of (1) detecting the presence of a signal, and (2) assigning this signal to a category which has definitive class properties (recognition). Detection: In the attempt to establish the characteristics of the stimulus for the detection response, amount of area and amount of edge of the object, have been advanced as determining factors. One group of investigators propose that as area is increased, the detection threshold will decrease systematically end that this response is independent of the shape of the object. These investigators have favored a view that as stimulus size increases a larger number of retinal receptors are fired and accordingly the detection threshold is reduced. On the other hand, other investigators hold that the detection response is dependent upon the amount of edge or perimeter of the object. These investigators, however, are divided into two theoretical groups. One group proposes that the contrast disparity at tile edge active-tea the postretinal neural mechanism and that differential stimulation of a row of receptors will account for brightness discrimination. The other group has advanced the theory that brightness discrimination results from the retinal scanning associated with eye-movements [TRUNCATED].
Thesis (Ph.D)--Boston University