Riccardo Brandolani¹, Claudio Galletti², Patrizia Fattori^2,3, Rossella Breveglieri^2,3, Martina Poletti¹; ¹Department of Brain & Cognitive Sciences, University of Rochester, ²Department of Biomedical and Neuromotor Sciences, University of Bologna, ³Interdepartmental center for industrial research-Aerospace, University of Bologna

It is well established that during gaze fixation, microsaccade directionality is influenced by covert shifts of spatial attention. However, the eye still moves between microsaccades due to ocular drift. Although drift is a slow movement resembling a random walk, recent research has highlighted not only its important contribution to fine spatial vision, but also the fact that the oculomotor system can exert some degree of control over this behavior. Here we examined whether drift directionality is impacted by covert shifts of attention and the temporal dynamics of ocular drift control in response to attentional cues. Participants (n = 7) performed a spatial cueing task while their right eye movements were recorded with a high-resolution Dual Purkinje Image eye tracker. Subjects fixated a central square while two colored circles appeared 5° to the left and right (Encoding window, 500 ms). Then the peripheral circles turned gray, and the central square changed into one of the two circles’ color cueing covert attention to one of the two sides (Direction window, 700–1000 ms). A low-contrast target then appeared in one of the circles (80% valid trials), and participants released a button upon its detection. Trials without microsaccades were analyzed (≈571 per participant). Reaction times to button release in these trials were modulated by cue validity confirming that microsaccades are not essential for attentional shifts. Trials were classified as toward, away, or other based on drift direction relative to the cue in the Directional cue window. Whereas we previously showed that microsaccades were biased toward the cue 240–340 ms post cue-onset, here we report that also drifts showed a bias but later in time around 470–550 ms. These findings show that ocular drift is modulated by covert attention, although with a slower dynamic compared to microsaccades.

Acknowledgements: This work was funded by NIH Grant EY029788 to Martina Poletti and NIH grant EY001319 to the Center for Visual Science. EU Marie Sklodowska-Curie grant agreement No 101086206 - PLACES.