Cortical Management of Spatial Resolution in Human Visual System

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・ Improvement of visual acuity as an aftereffect of the blur adaptationWe examined the influence of blur adaptation on the visual acuity (VA). In the experiment, the shift in VA was tracked in the course of adaptation and after the adaptation as well. The blurred visual field was provided by the foggy filter. The visual acuity was measured by a quick and simplified staircase method with Landolt C in every one minute. Subject's VA dropped when the foggy filter was inserted between the stimulus and the eye. Right after the drop, VA started rising and, after a while, it reached to the asymptote level. The moment the filter was removed, VA jumped up beyond the original VA. In a few minutes VA returned to the original level. The degree of temporary improvement in VA was larger with the hazier filter and longer adaptation period. This enhancement in VA is presumably caused by blur adaptation and its aftereffect. The original VA might not be the optimum performance of the eye. Rather it might … More be suppressed or controlled by the higher level of processing in the visual system.・ Influence of perceived size on the visual acuity measured with Landolt CIt has been shown that larger (or smaller) perceived size makes the letters' legibility higher (or lower) without changing their retinal size. Here we have examined whether such a change in the perceived size would affect the visual acuity as well. In the experiment, the visual acuity was measured by the constant stimuli method with the Landolt C. The stimulus was presented in a 3D stereoscopic view and its perceived size was controlled by changing the observer's convergence angle. Throughout the experiment the size of the retinal image was kept constant by keeping the viewing distance between the eye and the stimulus. Artificial pupils were placed in front of the observer's eyes to eliminate the accommodation effect. As a result, with the larger (or smaller) convergence angle, the stimulus appeared smaller (or larger) and the observer's visual acuity deteriorated (or enhanced). Our results suggest that the visual acuity, generally accepted as the most fundamental quality of early stage of visual system, can be affected by the size perception on the higher level of processing. Less