Microsaccades precisely relocate gaze in a high visual acuity

The possible visual functions of microsaccades have long been debated1–3. Proposed functions range from contributions to the prevention of image fading, the gradual disappearance of the visual percept experienced in the absence of retinal image motion4–6, to participation in the oculomotor strategy by which the eye maintains precise fixation on a cue7,8. An interesting hypothesis is that microsaccades may contribute to visual tasks that require high acuity9. According to this proposal, microsaccades serve the same function as larger saccades: as the visual system uses saccades to explore the scene, microsaccades enable exploration of a narrow region around the point of fixation when necessary. Experimental data have not supported this proposal. A seminal study, which examined microsaccades while observers aimed and shot a rifle and threaded a sewing needle, found that, in both conditions, microsaccade rates decrease just before the end of a trial, even when the task is successfully performed10. Furthermore, microsaccades are, on average, less frequent during these tasks than during maintained fixation on a small cue10. Similar results were also reported by a second study11. On the basis of these findings, it was concluded that microsaccades are detrimental and, therefore, suppressed during the execution of finel