Inhibitory processes and spatial bias after right hemisphere damage

Patients with lesions in the right hemisphere often show signs of unilateral neglect for the left side of space. Even in the absence of these signs, however, when exploring a visual scene these patients show an initial orientation of their attention towards the right side (Gainotti, D'Erme, & Bartolomeo, 1991). Some patients might be able to compensate for this spatial bias by actively inhibiting the rightward orientation after its occurrence; as a result, they would be capable of extending their exploration to the left part of space. However, due to conflicting demands on the same resource pool, a rightward bias in these patients is expected to reappear or be enhanced when inhibitory mechanisms are used to avoid producing prepotent but inappropriate responses. Eighteen normal controls and 40 right brain-damaged (RBD) patients (17 showing signs of left neglect, 23 without neglect) performed two reaction time tasks requiring manual motor responses to lateralised visual stimuli. In one task, trials in which a motor response was to be withheld (catch trials) were also presented. Regardless of whether they had neglect, patients responded more slowly to left-sided than to right-sided events in both tasks. The presence of catch trials further increased this rightward bias in patients without signs of neglect, but not in neglect patients, consistent with the hypothesis that RBD patients may use inhibitory processes to compensate for spatial bias.