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Matthew S. Peterson, Arthur F. Kramer; Covert shifts of attention precede involuntary eye movements. Journal of Vision 2002;2(7):163. doi: https://doi.org/10.1167/2.7.163.
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It is generally believed that covert attention and eye movements are inexorably linked, such that the planning of an eye movement automatically leads to a shift of covert attention to the saccade target. Previous research demonstrating this link has concentrated on voluntary eye movements. In two experiments, we examined whether covert attention precedes involuntary eye movements made to onsets. The task was to move the eyes to a small uniquely colored saccade target and to identify which of two letters were contained within. At the same time that the target changed color, an irrelevant onset appeared. To measure covert attention, we placed large response compatible or incompatible probes at the location of either the onset or the colored target. Probes were identifiable from central fixation and only visible between the presentation of the target and onset and the initiation of the first saccade. When the eyes moved to the intended color target, only probes at the location of the saccade target affected responses, and no trace of covert attention was found at the location of the onset. When the eyes made an involuntary saccade to the onset, probes at the onset affected response times, indicating that covert attention had preceded the eyes to the onset. However, probes at the color target also affected response times, but not when they were presented during the first 100 ms. This suggests that covert attention first made an involuntary shift to the onset and then made a corrective shift to the intended target, even though this was followed a short time later by an unintentional saccade to the onset. These results suggest that eye movements are a valid measure of the initial shift of covert attention. Consequently, this suggests that previous experiments showing only modest oculomotor capture by onsets are indicative of only modest covert attentional capture. Results are discussed in terms of a horse-race model between voluntary and involuntary signals.
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