The spatial interaction of visual attention and saccadic eye movements was investigated in a dual-task paradigm that required a target-directed saccade in combination with a letter discrimination task. Subjects had to saccade to locations within horizontal letter strings left and right of a central fixation cross. The performance in discriminating between the symbols "E" and "E", presented tachistoscopically before the saccade within the surrounding distractors was taken as a measure of visual attention. The data show that visual discrimination is best when discrimination stimulus and saccade target refer to the same object; discrimination at neighboring items is close to chance level. Also, it is not possible, in spite of prior knowledge of discrimination target position, to direct attention to the discrimination target while saccading to a spatially close saccade target. The data strongly argue for an obligatory and selective coupling of saccade programming and visual attention to one common target object. The results favor a model in which a single attentional mechanism selects objects for perceptual processing and recognition, and also provides the information necessary for motor action.

Many cells in retinotopic brain areas increase their activity when saccades (rapid eye movements) are about to bring stimuli into their receptive fields. Although previous work has attempted to look at the functional correlates of such predictive remapping, no study has explicitly tested for better attentional performance at the future retinal locations of attended targets. We found that, briefly before the eyes start moving, attention drawn to the targets of upcoming saccades also shifted to those retinal locations that the targets would cover once the eyes had moved, facilitating future movements. This suggests that presaccadic visual attention shifts serve to both improve presaccadic perceptual processing at the target locations and speed subsequent eye movements to their new postsaccadic locations. Predictive remapping of attention provides a sparse, efficient mechanism for keeping track of relevant parts of the scene when frequent rapid eye movements provoke retinal smear and temporal masking.

In a series of experiments, we examined the increase in saccade latency that is observed consistently when distractor stimuli are presented simultaneously with the saccade target at various nontarget locations. In the first experiment, targets and distractors were presented on the horizontal axis. We found that saccade latency was increased when distractors appeared at fixation and in the contralateral nontarget hemifield (at eccentricities < or = 10 degrees). In contrast, latency was unaffected by distractors presented along the ipsilateral target axis, but amplitude was increased as saccades tended to land at intermediate locations between the two stimuli (global effect). The effect of presenting distractors at various two-dimensional locations in both the target and nontarget hemifields then was examined, and the maximum latency increase again was observed when distractors appeared at fixation. Distractors presented on any of the eight principal axes in either hemifield, other than on the horizontal target axis, also increased latency. The relationship between the effects of distractors on latency and amplitude was reciprocal. Within approximately 20 degrees of the target axis itself, distractors affected saccade amplitude but not latency. In contrast, distractors presented outside this "window" increased saccade latency without affecting amplitude. A systematic quantitative relationship was revealed between the increase in latency and the ratio between target and distractor eccentricities. The latency increase was largest with small values of the ratio and reached a peak with distractors at the fixation location. The finding that the increase observed for more eccentric distractor locations fitted the same function as that at fixation shows that inhibitory effects operate over large areas of the visual field. The increase in latency under distractor conditions is interpreted in light of recent neurophysiological findings of inhibitory processes operating in the rostral region of the superior colliculus. Our results suggest that these inhibitory processes are not restricted to the central foveal region alone but operate over wider regions of the visual field.

Displacement of a visual target during a saccadic eye movement is normally detected only at a high threshold, implying that high-quality information about target position is not stored in the nervous system across the saccade. We show that blanking the target for 50-300 msec after a saccade restores sensitivity to the displacement. With blanking, subjects reliably detect displacements as small as 0.33 deg across 6 deg eye movements, with correspondingly steep psychophysical functions. Performance with blanking in a fixation control is inferior, evidence for a saccadic enhancement of sensitivity to image displacement. If blanking is delayed so that the target is visible immediately after the saccade in its displaced position, performance declines to non-blanking levels. Blanking the target before the saccade, and restoring it during the saccade, yields a similar but weaker effect. We interpret these results with a model in which the visual system searches for the postsaccadic goal target within a restricted spatiotemporal window. If it is not found, the assumption of stationarity of the world is broken and the system makes use of other information such as extraretinal signals for calibrating location.