Spatial and temporal contextual effects in early visual physiology and visual perception
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Temporal and spatial contextual effects strongly shape both perception and neuronal responses. The effects of adaptation, changes in perception and neuronal responses due to the preceding seconds or milliseconds of stimulus history, represent a form of rapid plasticity that allows for dynamic encoding of the current temporal context. Similarly, surround suppression, the suppression of neural responses to a stimulus by surrounding stimuli, represents a mechanism for encoding the current spatial environment. Due to their strong effects on both perception and physiology, adaptation and surround suppression are commonly employed as tools to study the physiological basis of perception. Thus, each has been extensively studied. Such studies have revealed similarities in the effects of adaptation and surround suppression, raising the possibility that they arise from common mechanisms to serve similar roles in visual processing and perception. The work presented in this dissertation explores how the effects of temporal and spatial context interact to shape neuronal responses and perception.;First, using microelectrode arrays implanted in V1 of anesthetized macaque monkeys, I show that adaptation of the surround can dramatically alter the effects of adaptation producing, novel effects never before reported in V1 and suggesting a tight mechanistic link between the effects of adaptation and surround suppression. The novel effects of adaptation found in V1 have been previously reported only in MT, an area downstream of V1 in the cortical processing hierarchy, suggesting that adaptation effects in MT may be inherited from V1. Therefore, spatial transfer experiments were performed in MT to test this idea. The results indicate that, at least on the timescale of several seconds, adaptation effects in MT are largely inherited from V1. Finally, the assertion that temporal and spatial contextual effects serve a similar role in perception was directly tested. Using a visual search task to test the effects of adaptation on salience, a known perceptual correlate of surround suppression, I show that adaptation can facilitate visual search. Taken together, these studies lend support to the idea that temporal and spatial contextual effects arise from shared physiological mechanisms to serve similar functions in perception and neuronal computation.
Source: Dissertation Abstracts International, Volume: 74-03(E), Section: B.;Advisors: Adam Kohn; Scott Nawy.