EFFECTS OF SPATIAL ATTENTION ON DIRECTIONAL MANUAL AND OCULAR RESPONSES

The aim of the present study was to investigate how spatial attention influences directional manual and saccadic reaction times. Two experim ents were carried out. In experiment 1 subjects were instructed to per form pointing responses toward targets that were located either in the same or the opposite hemifield with respect to the hemifield in which an imperative stimulus was presented. In experiment 2, they were inst ructed to make saccadic or pointing responses. The direction of the re sponses was indicated by the shape of the imperative stimulus. Reactio n time (RT), movement time, and, in experiment 2, saccadic trajectory were measured. The imperative stimulus location was either cued (endog enous attention) or uncued. In the latter case the imperative stimulus presentation attracted attention (exogenous attention). The main resu lts of the experiments were the following: First, exogenous attention markedly decreased the RTs when the required movement was directed tow ard the imperative stimulus location. This directional effect was much stronger for pointing than for ocular responses. Second, endogenously allocated attention did not influence differentially RTs of pointing responses directed toward or away the attended hemifield. In contrast, endogenous attention markedly favored the saccadic responses when mad e away from the cued hemifield. Third, regardless of cueing, the direc tion of movement affected both pointing and saccadic reaction times. S accadic reaction times were faster when the required movement was dire cted upward, while manual reaction times were faster when the movement was directed downward. Fourth, lateralized spatial attention deviated the trajectory of the saccades contralateral to the attention locatio n. This pattern of results supports the notion that spatial attention depends on the activation of the same sensorimotor circuits that progr am actions in space.