Spatiotemporal Characteristics of Visual Localization
Final rept. Aug 1988-Oct 1990,
SRI INTERNATIONAL MENLO PARK CA
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Psychophysical experiments were conducted to investigate how the human visual system determines the spatial structure of a visual scene. The theoretical basis of the research centers on three ideas that local spatial filters constitute an initial stage of contrast-encoding that the properties of these initial filters can affect accuracy of the judgements of the perceived separation and that the actual encoding of interobject separation occurs at a higher level of processing with its own properties. the properties of the higher levels of processing can be determined by controlling the input from the local spatial filters. Unlike thresholds that are determined primarily at lower levels of processing, thresholds for spatial relationships were found to be highly sensitive to the context in which the stimuli are presented and highly insensitive to those spatial and temporal characteristics that are known to play major roles in the determination of contrast detection thresholds. Context was found to affect both the threshold and the perceived value of interobject separations. Furthermore, the effects of context vary over time, being profound at short durations 100 ms and small or negligible at long durations 500 ms. The effects of context on the accuracy of judgements of spatial relationships at brief durations were found to depend on the spatial proximity and spatial similarity of the targets and the background context.
- Anatomy and Physiology