Ipsilesional biases in saccades but not perception after lesions of the human inferior parietal lobule

We examined the effects of chronic unilateral lesions to either the inferio r parietal lobe, or to the dorsolateral prefrontal cortex including the fro ntal eye fields (FEFs), upon human visual perception and saccades in tempor al-order-judgment (TOJ) tasks. Two visual events were presented on each tri al, one in each hemifield at various stimulus onset asynchronies (SOAs). In the saccade task, patients moved their eyes to whichever stimulus attracte d gaze first. In the perceptual-manual task, they pressed a button to indic ate which stimulus was perceived first. Frontal patients showed appropriate TOJs for visual targets in both tasks. Parietal patients showed appropriat e TOJs in the perceptual-manual but not the saccade task; their saccades te nded to be ipsilesional unless the contralesional target led substantially. This reveals a bias in saccade choice after parietal damage that cannot be attributed to deficient visual perception. These results challenge previou s claims that only anterior lesions produce motoric spatial biases in human s. However, they are in accord with recent neurophysiological evidence for parietal involvement in saccade generation, and also with suggestions that visuomotor transformations in the parietal lobe serving direct spatial moto r responses can dissociate from conscious perception as indicated by indire ct arbitrary responses.