Space and attention in parietal cortex

The space around us is represented not once but many times in parietal cort ex. These multiple representations encode locations and objects of interest in several egocentric reference frames. Stimulus representations are trans formed from the coordinates of receptor surfaces, such as the retina or the cochlea, into the coordinates of effecters, such as the eye, head, or hand . The transformation is accomplished by dynamic updating of spatial represe ntations in conjunction with voluntary movements. This direct sensory-to-mo tor coordinate transformation obviates the need for a single representation of space in environmental coordinates. In addition to representing object locations in motoric coordinates, parietal neurons exhibit strong modulatio n by attention. Both top-down and bottom-up mechanisms of attention contrib ute to the enhancement of visual responses. The saliance of a stimulus is t he primary factor in determining the neural response to it. Although pariet al neurons represent objects in motor coordinates, visual responses are ind ependent of the intention to perform specific motor acts.