FRONTAL-LOBE MECHANISMS SUBSERVING VISION-FOR-ACTION VERSUS VISION-FOR-PERCEPTION

In the typical course of daily events, we often gaze at an object, att end to its features and its place, reach toward it and grasp it, all w ith an awareness of what we are doing at the time. But behavior is not always thus. Gaze, attention, limb movement direction and awareness c an be behaviorally dissociated from each other, and this review focuse s on one such dissociation: that between the perception of an object a nd the use of that object's inherent spatial and nonspatial informatio n for mediating visuomotor control. We review evidence that partially different neuronal systems underlie these two aspects of visual inform ation processing. In neurophysiological studies of the primate frontal lobe, it has been possible to demonstrate that neural signals appeari ng to be visual responses reflect, at least in part, the motor signifi cance of a stimulus. This finding has been confirmed, in separate stud ies, for both spatial and nonspatial visual information and supports t he hypothesis that some frontal cortex activity reflects the selection and guidance of action rather than the properties of visual stimuli, per se. These findings are discussed in the context of neuropsychologi cal studies indicating that accurate and appropriate movements are pos sible without perceptual awareness of the information guiding those mo vements.