Egocentric body -centered coordinates modulate visuomotor performance.

Abstract

Studies of neglect patients have suggested that egocentric coordinates may play an important role in spatially-oriented behavior. Specifically, it has been proposed that damage to the parietal lobe, an area of the brain associated with neglect, causes a disturbance in the central representation of body-centered coordinates, which in turn causes a bias in visuomotor processes away from the contralateral side and toward the ipsilesional side. This dissertation investigated this assertion by testing neurologically-intact adults in a series of 5 experiments requiring visual detection of lateralized light flashes. The findings indicate that: (1) a rightward displacement of the body midline causes a rightward bias in visuomotor processes in neurologically-intact as, measured by response latencies to lateralized targets; (2) rightward rotation also evokes an increase in visual sensitivity to the right-sided target and a decrease in sensitivity to the left-sided target; and (3) the effects of leftward rotation on response latency and sensitivity are weak to nonexistent; however, response bias may be affected by left but not right rotation. The finding of a rightward bias in visuomotor processes during rightward rotation supports theories of a disturbed central representation of body-centered coordinates in neglect. It also illustrates that alterations in the body-centered egocentric coordinate frame in neurologically-intact individuals can lead to a bias in perceptual-motor behavior. This finding appears to be the first illustration of an effect of body-centered coordinates on performance in a visuomotor task in neurologically-intact subjects.