Unilateral posterior parietal lobe lesions affect representation of visual space

This study assessed accuracy of visually perceived vertical and trunk median plane orientation in 41 subjects: 17 had unilateral brain lesions including the posterior parietal lobe (PPL), 8 had lesions outside PPL, and 16 were neurologically normal. Vertical perception errors clearly increased with size of unilateral lesions to PPL and posterior superior temporal gyrus (PSTG). Median plane perception errors increased only slightly with size of unilateral lesions to frontal lobe premotor areas and supramarginal gyrus. These results are compatible with the hypothesis that accurate visual vertical perception depends critically on intact PPL and PSTG in both cerebral hemispheres while accurate median plane perception likely involves a bihemispheric network that can compensate for lesions to one hemisphere.