Mechanisms of visual spatial neglect. Absence of directional hypokinesia in spatial exploration.

This study examines whether visuospatial neglect derives from failure in directing hand movements to the left (directional hypokinesia), or from loss of mental representation of the left side of space. Forty right brain-lesioned patients, 28 of whom revealed mild, moderate, or severe neglect in clock drawing and cancellation tasks, were asked to search for concealed targets on a stimulus display board, by either (1) moving a covering panel with a small window until the target appeared, or (2) moving the stimulus display board beneath a stationary covering panel until the target became visible through the window. In the second procedure, the direction of physical space exploration and hand movement is reversed, so that in order to bring a target from the right side of the stimulus into view (under the window) the entire display board had to be moved to the left. This pair of procedures was supplemented by an analogous pair of visual tasks in which the entire display board was visible during the search. As expected, response times were generally longer for targets located on the left side of the display board; however, the direction of required hand movement (left vs right) did not have a significant effect on response times, irrespective of the degree of clinically assessed neglect.