Contributions of fixational eye movements to the discrimination of briefly presented stimuli.

Although it is known that images tend to disappear when they are stabilized on the retina for tens of seconds or minutes, the possible functions of fixational movements during the brief periods of visual fixation that occur during natural viewing remain controversial. Studies that investigated the retinal stabilization of stimuli presented for less than a few seconds have observed neither decrement in contrast sensitivity nor image fading. In this study, we analyzed the effect of retinal stabilization on discriminating the orientation of a low-contrast and noisy small bar that was displayed for either 500 ms or 2 s. The bar was randomly tilted by 45 degrees either clockwise or counterclockwise. For both exposure durations, percentages of correct discrimination were significantly lower under conditions of visual stabilization than in the presence of the normally moving retinal image. These results are consistent with the predictions of recent computational models that simulated neuronal responses in the early visual system during oculomotor activity and support the hypothesis that visual processes deteriorate rapidly in the absence of retinal image motion.