A deficit in contralesional object representation associated with attentional limitations after parietal damage

Stankiewicz, Hummel, and Cooper (1998) proposed that detailed coding of part-whole relations for objects is contingent on objects being attended. We report a neuropsychological test of this assertion. We examined the effects of left-right reflection on object matching in a group of patients with parietal damage and impaired attention to the contralesional side of space (Experiment 1). The patients were poor at matching objects subject to left-right reflection, relative to identical stimuli (Experiment 2). This was not due to a lack of sensitivity to information on the contralesional side. In a subsequent study, the patients were better at matching identical whole objects at fixation than when they just received half the object in their ipsilesional field (Experiment 3). However, unlike both nonlesioned controls and control patients with frontal lesions, the parietal patients were unaffected by altering the relative spatial locations of object features in their contralesional field (Experiment 4). The basic result, of poor performance with left-right-reflected items, was also replicated using a priming rather than an explicit matching procedure (Experiment 5). These results provide confirmation that visual attention, mediated by the posterior parietal cortex, is important for generating part-whole codes that facilitate the matching of mirror-reflected objects.