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Gain adaptation of saccadic eye movements is the process whereby the size of the saccade is gradually modified if the target is consistently and surreptitiously displaced during the saccade. Because one attends to the saccade target before each saccade, we asked whether covert shifts of exogenous attention might themselves be adaptable. We did this by presenting a peripheral cue and then displacing it by 3 deg after an interval equal to the average time required for attention to shift from a central to a peripheral cue. This interval, as well as the location at which attention landed, was determined by a modification of the line-motion illusion, in which a line appears to shoot from a previously cued location. We found that this adaptation paradigm produced consistent gradual reductions (for back-steps) or increases (for forward-steps) in the magnitude of the shifts of attention. Like saccadic adaptation, adaptation of shifts of attention could be manipulated independently for rightward and leftward shifts. Furthermore, the backward adaptation paradigm also decreased the magnitude of subsequent saccades, even though no saccades had been made during the attentional adaptation. This argues that saccades are targeted to the locus of attention, and when this locus is systematically shifted, so too are subsequent saccades. In conclusion, the adaptability of shifts of attention suggests that attentional shifts, like saccades, are recalibrated using a spatial error signal.
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