Microsaccades and attention in a high-acuity visual alignment task

ABSTRACT While aiming and shooting, we make tiny eye movements called microsaccades that shift gaze between task-relevant objects within a small region. However, in the brief period before pressing trigger, microsaccades are suppressed. This might be due to the lack of the requirement to shift gaze as the retinal images of the two objects start overlapping on fovea. Or we might be actively suppressing microsaccades to prevent any disturbances in visual perception caused by microsaccades around the time of their occurrence and their subsequent effect on shooting performance. In this study we looked at microsaccade rate while participants performed a simulated shooting task under two conditions: normal viewing in which they moved their eyes freely and eccentric condition in which they maintained gaze on a fixed target while performing shooting task at 5° eccentricity. As expected, microsaccade rate dropped at the end of the task in the normal viewing condition. However, we found the same for the eccentric condition in which microsaccade did not shift gaze between the task objects. Microsaccades are also produced in response to shifts in covert attention. To test whether disengagement of covert attention from eccentric shooting location caused the drop in microsaccade rate, we monitored participant’s spatial attention location by employing a RSVP task simultaneously at a location opposite to the shooting task. Target letter detection at RSVP location did not improve during the drop in microsaccade rate, suggesting that covert attention was maintained at the shooting task location. We conclude that in addition to their usual gaze-shifting function, microsaccades during fine acuity tasks might be modulated by cognitive processes other than spatial attention.