A quantitative measure for short-term cortical plasticity in human vision.

The human visual system is normally very good at determining the relative positions of objects in space, but under certain conditions contextual influences can cause significant errors in this process. We studied spatial localization around an artificial scotoma, a small mask that occludes part of the visual field while a dynamic pattern is shown over a surrounding region, and found that the ability to determine the position of short line segments was strongly biased toward the interior of the scotoma. We attribute this "shift" or misassignment of position to receptive field (RF) expansions within the artificial scotoma as seen in recent physiological studies. Furthermore, our findings show that this shift begins within 1 sec of stimulus presentation, suggesting that RFs are constantly altered by their local context and that these dynamics are a part of normal vision.