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Michele Rucci, Gaelle Desbordes, Ramon Iovin, Fabrizio Santini; Contributions of fixational eye movements to visual discrimination. Journal of Vision 2006;6(6):104. doi: https://doi.org/10.1167/6.6.104.
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© ARVO (1962-2015); The Authors (2016-present)
During natural viewing, small eye movements prevent the maintenance of a steady direction of gaze. It is known that images tend to disappear when they are stabilized on the retina for several seconds. However, the possible functions of the physiological motion of the retinal image during the naturally brief periods of fixation remain controversial. Here, we show that fixational eye movements improve the discrimination of briefly flashed, high spatial frequency gratings. In a forced-choice discrimination task, subjects reported whether a noisy grating displayed for 1s was tilted by 45° clockwise or counterclockwise. Discrimination percentages were significantly higher in the presence of the normally moving retinal image than under retinal stabilization in the case of high-frequency gratings, but not for low-frequency gratings. Unlike previous experiments, retinal stabilization was accomplished by means of a gaze-contingent display system, which processed in real time the eye movements measured by a DPI eye-tracker. This approach enabled rigorous comparison between the two conditions of normal retinal motion and retinal stabilization. It enabled to (a) selectively stabilize the stimulus after a saccade, a condition that preserves the normal jittering of the eye, and (b) to randomly interleave trials with and without retinal image motion. These results are consistent with our recent hypothesis that fixational eye movements are part of an efficient strategy for encoding natural stimuli. According to this proposal, fixational instability enhances high spatial frequencies and attenuates low spatial harmonics in a way that counter-balances the scale-invariant structure of natural images (Supported by NIH-EY015732-01).
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