Spatial attention and eye movements.

We previously showed that when attention is allocated to the right or left of the fixation point, saccades directed to targets located above or below the fixation point deviate contralateral to the attention locus. In the present study, we examined how general this phenomenon is and whether the amount of saccade deviation depends on the location of attention with respect to that of the saccade target. Three experiments were carried out. In experiment 1 the location of the imperative stimulus was uncued. Its presentation exogenously directed attention to its location. In experiment 2 the location of the imperative stimulus was cued by a central cognitive cue. In this experiment attention was endogenously directed to the imperative stimulus location before its presentation (expectancy paradigm). In experiment 3 all stimulus boxes contained a possible imperative stimulus at the display presentation. A central cue, presented subsequently, indicated which of them had to be used for the saccade. In this experiment attention was endogenously directed to the imperative stimulus, but after its presentation (no-expectancy paradigm). The results showed that, regardless of how attention was directed to the imperative stimulus, the vertical saccades deviated contralateral to the attention location. The deviation was larger when attention was in the upper field and the saccade was directed upward ("same hemifield" condition) than when attention was in the upper field and the saccade was directed downward ("opposite hemifield" condition). The same relationship between the "same hemifield" condition and "opposite hemifield" condition was found when attention was in the lower field. Saccadic reaction times (SRTs) were shortest in experiment 2 and longest in experiment 3. In experiment 2, SRTs of the "same hemifield" condition were significantly longer than those of the "opposite hemifield" condition. Taken altogether, these results strongly support the notion that attention allocation in space leads to an activation of oculomotor circuits, in spite of eye immobility. The possible mechanisms responsible for saccade deviations and for greater saccade deviations when attention is in the same hemifield as the programmed ocular saccade are discussed.