Effects of exogenous and endogenous attention on visually guided hand movements.

Attention can be directed to a peripheral location by either a peripheral visual stimulus or a central cue indicating the likely location of an upcoming target. The present study examined the effects of peripheral and central cuing on reaching. When the target was presented in a location different from that indicated by either type of attentional cue, movements with short latencies (<200 ms) were mostly initiated toward the cued location. When the target was presented 90 degrees away from the direction indicated by the attentional cue, movements with intermediate latencies (200-300 ms) were often initiated in directions intermediate between the cue and the target, and the latencies of movements initiated toward the target were prolonged. This suggests that the location of an attentional cue was utilized as an initial value in the process specifying movement direction, and this was gradually modified by signals related to target location. When peripheral and central cues were combined in the same trials, effects of peripheral cues were substantially diminished, compared to when they were examined separately. Furthermore, movements were seldom initiated in directions intermediate between the two cues, suggesting that effects of peripheral and central cues are combined independently from the process that specifies movement direction. Copyright 1999 Elsevier Science B.V.