Abstract
Microsaccades are miniscule motor acts widely assumed to be generated in complete absence of the observers’ awareness. Recent evidence, however, demonstrated that microsaccades can be generated voluntarily and with high precision (Poletti et al. 2020), suggesting conscious accessibility. Here, we examined if observers can recognize the microsaccades they spontaneously generate and, moreover, if microsaccade-contingent visual stimulus presentations alter the awareness of these involuntary motor acts. We displayed a vertically oriented grating with a rapid temporal phase shift (>60 Hz) that rendered the stimulus invisible during slow fixational eye movements. The grating became briefly visible when it slowed down on the retina, either because the observer spontaneously generated a microsaccade in the direction of the phase shift (active condition) or when the retinal consequence of a previous microsaccade was replayed back to the observer (replay condition). In additional control trials, no stimulus was displayed at all. At the end of each trial, observers reported first if they perceived the stimulus and second whether they believed to have generated a microsaccade. Depending on the answers to these questions, observers additionally rated their confidence that the perceived stimulus was or was not caused by a microsaccade. In both the active and replay condition, observers were highly sensitive to the stimulus in trials in which their microsaccade—or the replayed microsaccade—matched the stimulus’ phase shift’s direction and velocity. This suggests that the retinal consequences of microsaccades alone (i.e., retinal motion) account for the observed sensitivity. In contrast, observers’ sensitivity to whether they generated a microsaccade was very low, in particular, when a stimulus was displayed. Finally, confidence about the cause of the stimulus percept was comparable for active and replay condition trials. Together, these results suggest that microsaccades, if generated spontaneously, indeed escape awareness.