Spatiotemporal Characteristics of Visual Localization.
Annual rept. 30 Sep 83-29 Sep 84,
SRI INTERNATIONAL MENLO PARK CA
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We continue to study the spatial and temporal characteristics of relative spatial localization, seeking to establish conditions in which it can be isolated from the processes underlying the detection of motion and form. Thus far we have found that stabilizing the retinal image degrades localization accuracy by a factor of 2, and further that this degradation does not result from a reduction in the apparent contrast of the stimulus. Drifting the stimulus slowly at a velocity known to restore contrast sensitivity to normal unstabilized values does not improve localization accuracy noticeably. However, localization accuracy is restored to normal if the otherwise-stabilized stimulus is moved rapidly. We have also found that localization accuracy improves with increasing contrast for contrasts significantly above the detection threshold, supporting our hypothesis that location and detection are parallel visual processes. We have also found that localization accuracy is as good at large object separations as it is at very small separations the vernier acuity range where sensitivity is known to be extremely acute. Thus, spatial localization is not primarily a foveal function that is degraded elsewhere, but rather a general visual ability.