Dynamic effective visual-field for chromatic and luminance contrast perception

PURPOSE: Visual function degrades in peripheral visual field. We studied how chromatic and luminance contrast difference-thresholds increased in the periphery when we observed a natural scene with frequent eye movements. METHODS A natural scene was presented on a CRT as a stimulus. The subject observered a stimulus with a restricted visual window of a certain size, which followed his eye movements in real time. In the window the stimulus contrast was not changed whereas in the surround of the window the stimulus contrast was reduced from 100% to 0%. We measured thresholds of detecting contrast difference between the center and the surround visual fields of the stimulus. The stimulus contrast was changed in either chromatic or luminance. The subject observed two pictures successively; one contained degraded surround and the other did not. The observer's task was to report which of the pictures was changed at the surround. RESULTS The results show that the diffrence threshold slightly increases with increasing size of the window. It was determined that the horizontal size of the window was 84 degrees for 90% of chromatic contrast, 87 degrees for 80% of luminance contrast. CONCLUSION During eye movements, we could detect small difference in chromatic and luminance contrast at the peripheral visual field.