In human observers, prolonged viewing of a moving target causes a subsequently viewed stationary target to appear to move slowly in the opposite direction. Prolonged viewing also results in other motion aftereffects, including underestimates of the perceived velocity of subsequently viewed targets. These perceptual aftereffects are thought to be due to adaptation (the decrease in response following prolonged stimulation) of neurons in the visual cortex. The neural basis for motion perception was explored by studying the responses of single neurons in area 18 of the cat visual cortex to prolonged stimulus movement. The relationship between adaptation and velocity aftereffects was examined by comparing responses evoked by sinusoidal luminance gratings drifting at various rates before and after prolonged exposure to a grating drifting at a constant rate. / Virtually all neurons in area 18 exhibited adaptation. For most neurons, the time course of adaptation was described adequately by a simple exponential function. However, in a small number of neurons, the time course of adaptation was better described by a second-order equation like those used to model systems controlled by negative feedback. Exposure to rapidly drifting gratings resulted in more rapid and extensive adaptation than exposure to slowly drifting gratings. Neural aftereffects were bidirectional, and were most prominent at or above a neuron's preferred temporal frequency, regardless of the adapting temporal frequency. / The neuronal results were compared to velocity aftereffects, in which prolonged exposure to a moving target causes observers to underestimate the velocity of subsequently viewed targets. A vector-sum model was used to compute velocity based upon the pooled responses of neurons tuned to different temporal frequencies. When adaptation like that observed in area 18 neurons was incorporated into the model, the velocity of stimuli at or above the adapting velocity were underestimated, in agreement with human psychophysical data. This suggests that adaptation of visual cortical neurons may represent the substrate for velocity and other motion-related aftereffects. / Source: Dissertation Abstracts International, Volume: 52-08, Section: B, page: 4049. / Major Professor: Mark A. Berkley. / Thesis (Ph.D.)--The Florida State University, 1991.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_76481 |
| Contributors | O'Keefe, Lawrence P., Jr., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 103 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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