Perceptual, premotor and motor factors in the performance of a delayed-reaching task by subjects with unilateral spatial neglect.

We used a computerized delayed-reaching task with a simple reaction time (RT) to investigate the visuo-motor and spatio-temporal performance of right brain-damaged (RBD) patients with unilateral spatial neglect (USN). Fifty-three RBD patients (22 with and 31 without USN) and 25 controls performed the tasks. We recorded the following data: the first RT (RT-1), which is thought to reflect the detection of the target position (the perceptual factor); the second RT (RT-2), which represents the initiation of reaching (the motor initiation aspect of premotor factors); the movement time (MT), which is hypothesized to reflect the "pure" motor component of the task. RBD patients with both USN and hemianopia demonstrated significantly longer RTs towards the left than towards the right for both the RT-1 and the RT-2. Among the RBD patients without hemianopia, the laterality index (left side/right side) of the RT-1 in those with USN was significantly greater than in those without USN or the controls. Among the three groups, there were no significant differences between the laterality indices of either the RT-2s or the MTs. These results suggest that the impairment of leftward movement in RBD patients with USN might be caused primarily by a perceptual impairment rather than an impairment in motor initiation, and is certainly not a "pure" motor impairment.