Fixational Eye Movements Are Not an Index of Covert Attention

Abstract

The debate about the nature of fixational eye movements has revived recently with the claim that microsaccades reflect the direction of attentional shifts. A number of studies have shown an association between the direction of attentional cues and the direction of microsaccades. We sought to determine whether microsaccades in attentional tasks are causally related to behavior. Is reaction time (RT) faster when microsaccades point toward the target than when they point in the opposite direction? We used a dual-Purkinje-image eyetracker to measure gaze position while 3 observers (2 of the authors, 1 naive observer) performed an attentional cuing task under three different response conditions: saccadic localization, manual localization, and manual detection. Critical trials were those on which microsaccades moved away from the cue. On these trials, RTs were slower when microsaccades were oriented toward the target than when they were oriented away from the target. We obtained similar results for direction of drift. Cues, not fixational eye movements, predicted behavior.

Spontaneous Microsaccades Reflect Shifts in Covert Attention

“…Such studies examined stimulustriggered microsaccades that were evoked by the stimuli (including the attention cues) used in the experiment (Hafed and Clark, 2002;Engbert and Kliegl, 2003;Laubrock et al, 2005Laubrock et al, , 2007Laubrock et al, , 2010Hafed et al, 2011). Although initially controversial (Horowitz et al, 2007), it has been established clearly and convincingly that such stimulus-triggered microsaccades modulate with attention (Laubrock et al, 2010). However, it was conceivable that spontaneous microsaccades are governed by a distinct physiological mechanism that is not influenced by attention.…”

Microsaccades: a neurophysiological analysis

“…200 ms following the cue) [12,13,18,73,75,76,79,80] (but see Refs [74,81,82] for a counterpoint). Some of the apparent disagreement across studies might be explained by engagement of endogenous versus exogenous attention in different experimental tasks.…”

“…A related topic of ongoing debate is whether biases in microsaccade directions indicate shifts in covert attention [12,13,79] and/or motor programming [42,78,82,84].…”

A computer vision model for visual-object-based attention and eye movements

“…Attentional shifts can be decoupled and disengaged from eye movements to freely select interesting targets without eye movements [11], [15]; • Attention plays a crucial role in the control and sequence of eye movements and visual perception. Attention filters out visual backgrounds and ensure that eye movements are programmed solely on the objects, features, locations, or groups selected by attention.…”

“…The term "grouping" may be confused with perceptual grouping and the term "proto-object" at least lacks the power to represent physical and conceptual objects, object-based and feature-based selection, and segmenting of scenes into units with attention. Attentional shifts and eye movements (gaze shifts) are both modelled in the way of which they not only can be coupled and cooperated for flexible visual selection but also particularly can be separated or dis-coupled for their different function roles -an important feature of human vision [11], [15]. Attention through integrated or biased competition operates upon the common underlying attentional circuits, responding with visual selection by locations, features, objects, and groups depending on the nature of attended targets and visual tasks.…”