title: Spontaneous microsaccades reflect shifts in covert attention.
abstract: Microsaccade rate during fixation is modulated by the presentation of a visual stimulus. When the stimulus is an endogenous attention cue, the ensuing microsaccades tend to be directed toward the cue. This finding has been taken as evidence that microsaccades index the locus of spatial attention. But the vast majority of microsaccades that subjects make are not triggered by visual stimuli. Under natural viewing conditions, spontaneous microsaccades occur frequently (2-3 Hz), even in the absence of a stimulus or a task. While spontaneous microsaccades may depend on low-level visual demands, such as retinal fatigue, image fading, or fixation shifts, it is unknown whether their occurrence corresponds to changes in the attentional state. We developed a protocol to measure whether spontaneous microsaccades reflect shifts in spatial attention. Human subjects fixated a cross while microsaccades were detected from streaming eye-position data. Detection of a microsaccade triggered the appearance of a peripheral ring of grating patches, which were followed by an arrow (a postcue) indicating one of them as the target. The target was either congruent or incongruent (opposite) with respect to the direction of the microsaccade (which preceded the stimulus). Subjects reported the tilt of the target (clockwise or counterclockwise relative to vertical). We found that accuracy was higher for congruent than for incongruent trials. We conclude that the direction of spontaneous microsaccades is inherently linked to shifts in spatial attention.
authors.affiliation: School of Psychological Sciences and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 6997801, Israel, and shlomitgr@tau.ac.il.
authors.forename: Shlomit
authors.initials: S
authors.lastname: Yuval-Greenberg
authors.affiliation: Department of Psychology and Center for Neural Science, New York University, New York, New York 10003.
authors.forename: Elisha P
authors.initials: EP
authors.lastname: Merriam
authors.affiliation: Department of Psychology and Center for Neural Science, New York University, New York, New York 10003.
authors.forename: David J
authors.initials: DJ
authors.lastname: Heeger
mesh_terms: D001288:Attention / Q000502:physiology*; D003463:Cues; D005133:Eye Movements / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D010775:Photic Stimulation; D011597:Psychomotor Performance; D012438:Saccades / Q000502:physiology*; D014796:Visual Perception
keywords: covert attention; eye movements; fixation; microsaccades; spatial attention; visual perception