The influence of contralesional targets on the cancellation of ipsilesional targets in unilateral neglect.

Neglect of contralesional stimuli and perseverative behavior on ipsilesional stimuli may co-occur on a target cancellation task. Our aim was to investigate whether the presence vs. absence of contralesional targets can modify perseveration on ipsilesional targets. We studied four right brain-damaged patients with left neglect and perseverative behavior on screening cancellation tasks. We compared their cancellation performance in two conditions: (i) targets equally distributed on both sides of space and (ii) targets confined to the right side. One patient showed no significant difference in perseveration between these two conditions; in contrast, three patients perseverated significantly more in condition (i) than in condition (ii). These results suggest that, at least in some patients, information from the 'neglected' targets is not completely lost, but rather it affects behavior in the ipsilesional side. The traditional dichotomy 'bad space-good space' would not apply here.