Integration of visual and somatosensory target information in goal-directed eye and arm movements

In this study, we compared separate and coordinated eye and hand movements towards visual or somatosensory target stimuli in a dark room, where no vis ual position information about the hand could be obtained. Experiment 1 sho wed that saccadic reaction times (RTs) were longer when directed to somatos ensory targets than when directed to visual targets in both single- and dua l-task conditions. However, for hand movements, this pattern was only found in the dual-task condition and not in the single-task condition. Experimen t 1 also showed that correlations between saccadic and hand RTs were signif icantly higher when directed towards somatosensory targets than when direct ed towards visual targets. Importantly, experiment 2 indicated that this wa s not caused by differences in processing times at a perceptual level. Furt hermore, hand-pointing accuracy was found to be higher when subjects had to move their eyes as well (dual task) compared to a single-task hand movemen t. However, this effect was more pronounced for movements to visual targets than to somatosensory targets. A schematic model of sensorimotor transform ations for saccadic eye and goal-directed hand movements is proposed and po ssible shared mechanisms of the two motor systems are discussed.