The visual functions of microsaccades have been the subject of intense debates. We have recently shown that microsaccades precisely relocate the preferred retinal locus according to the task demands (Ko et al., 2010), bringing the stimulus on the most suited retinal region within the foveola (Poletti et al., 2013). However, it has long been questioned whether temporal transients caused by microsaccades are also beneficial. To address this question, we first conducted time-frequency analyses of the retinal input relative to the occurrence of microsaccades. We show that microsaccades contribute slightly more temporal power than ocular drift (the incessant intersaccadic eye movement) for stimuli below 10 cycles/deg suggesting a potential benefit in the low-frequency range. We then measured the influences of microsaccades on contrast sensitivity in a 2AFC experiment in which subjects reported the orientation (?±45?°) of a Gabor stimulus at either 0.8 or 10 cycles/deg. We show that, in agreement with theoretical predictions, contrast sensitivity slightly improved in the trials with one or more microsaccades compared to drift-only trials. As predicted, this effect was limited to the low spatial frequency stimulus. No benefit of microsaccades on contrast sensitivity was observed with a 10 cycles/deg grating. In both cases, however, all subjects exhibited a substantial suppression of microsaccades (approximately 70%) during the period of stimulus presentation. This suppression was also present with the low spatial frequency grating, in spite of the small perceptual benefit of microsaccades. In sum, our theoretical and experimental results show that, even though microsaccadic transients slightly improve sensitivity to low spatial frequencies, observers do not normally take advantage of them. This behavior makes sense with the localized stimuli of natural environment, where the detrimental consequences of bringing the preferred fixation locus away from the region of interest would outweigh the small perceptual benefit resulting from microsaccade temporal modulations.
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