Microsaccades precisely relocate gaze in a high visual acuity task.

The image on the retina is never stationary. Microscopic relocations of gaze, known as microsaccades, occur even during steady fixation. It has long been thought that microsaccades enable exploration of small regions in the scene in the same way saccades are normally used to scan larger regions. This hypothesis, however, has remained controversial, as it is believed that microsaccades are suppressed during fine spatial judgments. We examined the eye movements of human observers in a high-acuity visuomotor task, the threading of a needle in a computer-simulated virtual environment. Using a method for gaze-contingent display that enables accurate localization of the line of sight, we found that microsaccades precisely move the eye to nearby regions of interest and are dynamically modulated by the ongoing demands of the task. These results indicate that microsaccades are part of the oculomotor strategy by which the visual system acquires fine spatial detail.