A QUANTITATIVE MEASURE FOR SHORT-TERM CORTICAL PLASTICITY IN HUMAN VISION

The human visual system is normally very good at determining the relat ive positions of objects in space, but under certain conditions contex tual influences can cause significant errors in this process. We studi ed spatial localization around an artificial scotoma, a small mask tha t occludes part of the visual field while a dynamic pattern is shown o ver a surrounding region, and found that the ability to determine the position of short line segments was strongly biased toward the interio r of the scotoma. We attribute this ''shift'' or misassignment of posi tion to receptive field (RF) expansions within the artificial scotoma as seen in recent physiological studies. Furthermore, our findings sho w that this shift begins within 1 sec of stimulus presentation, sugges ting that RFs are constantly altered by their local context and that t hese dynamics are a part of normal vision.