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Shun-nan Yang; Visuomotor Control Based on Partial Evaluation of Object Features. Journal of Vision 2004;4(8):652. doi: 10.1167/4.8.652.
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Individuals use visual features to guide eye movements, including when they withhold undesired movements to salient but distracting stimuli. The current study investigates how visual features are utilized in the decision-making process of holding gaze. Subjects were asked to track a white square making consecutive horizontal jumps across a screen (4 displacement followed by a 500ms stationary interval and 50ms blank). They were asked to hold their gaze at a stimulus with a cued feature change (e.g., green target), but not at one with a different feature change (e.g., red target). To describe saccade likelihood over time, hazard functions of the subject's fixations when a stimulus with feature changes appeared were calculated, and compared to fixations preceding stimuli without feature changes. The results reveal an early reduction of saccade likelihood associated with the onset of a stimulus with a relevant feature change. Saccades bringing the eyes to the stimulus were affected, although the instruction was to withhold the saccade leaving it. Furthermore, the early suppression occurred when the feature change was related to the cued feature(s), but not necessarily its exact attribute(s). For example, a green square had a similar suppression effect on trials in which red was the cued feature. When the cue was conjunctional (e.g., green-triangle), any change of related features elicited a similar effect. In contrast, saccades initiated following fixation on the target stimulus were affected only when the feature change was identical to what was cued. These results suggest there is an early component of saccade inhibition that coincides with the onset of the target stimulus. It likely results from the partial evaluation of features, allowing early inhibition to occur. This is interpreted within a framework of sensorimotor processing involving the dynamic access of primitive information by frontal cortical regions.
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