Different fixational eye movements mediate the prevention and the reversal of visual fading

Key points Fixational eye movements (microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different fixational eye movements influence this process is a matter of debate. Previous studies confounded the reversal of fading (where vision is restored after fading) with its prevention (where fading is blocked before it happens). We found that, whereas microsaccades are most important to reversing fading, both microsaccades and drift help to prevent it. Drift's contribution to preventing fading is potentially larger than that of microsaccades, but microsaccades prevent fading with higher efficacy than drift. Microsaccades prevent foveal and peripheral fading in an equivalent fashion, and microsaccadic efficacy does not depend on microsaccade size, number, or direction; further, faster drift may prevent fading better than slower drift. These combined findings help reconcile the long‐standing controversy concerning the roles of microsaccades and drift in visibility during fixation.Abstract Fixational eye movements (FEMs; including microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different FEM types influence this process is a matter of debate. Attempts to answer this question have been hampered by the failure to distinguish between the prevention of fading (where fading is blocked before it happens in the first place) and the reversal of fading (where vision is restored after fading has already occurred). Because fading during fixation is a detriment to clear vision, the prevention of fading, which avoids visual degradation before it happens, is a more desirable scenario than improving visibility after fading has occurred. Yet previous studies have not examined the role of FEMs in the prevention of fading, but have focused on visual restoration instead. Here we set out to determine the differential contributions and efficacies of microsaccades and drift to preventing fading in human vision. Our results indicate that both microsaccades and drift mediate the prevention of visual fading. We also found that drift is a potentially larger contributor to preventing fading than microsaccades, although microsaccades are more effective than drift. Microsaccades moreover prevented foveal and peripheral fading in an equivalent fashion, and their efficacy was independent of their size, number, and direction. Our data also suggest that faster drift may prevent fading better than slower drift. These findings may help to reconcile the long‐standing controversy concerning the comparative roles of microsaccades and drift in visibility during fixation.