FMRI confirmation of a neurological dissociation between perceiving objects and grasping them

Abstract

Some of the most compelling evidence for the distinction between vision-for-perception and vision-for-action has come from studies of patient DF who developed visual form agnosia following an anoxic episode. DF is able to use visual information about the size, shape, and orientation of objects to control her grasping movements despite the fact that she is unable to perceive those same object attributes. On the basis of these results and some early structural MR data, we proposed that the anoxia had interrupted the normal flow of object form information into her ventral stream without affecting the processing of object form information by her dorsal stream. Recently we confirmed this idea in an fMRI experiment. New anatomical MR images showed that the lateral occipital cortex (LOC), a ventral-stream area implicated in object recognition, is severely damaged in DF. A comparison of activation with line drawings of objects and scrambled versions of the same drawings revealed no differential activation in this or the surrounding cortex. Objects with color and visual texture did result in significant but atypical activation in areas outside of LOC. In contrast, when DF grasped objects that varied in size and orientation, she showed relatively normal activation in the anterior intraparietal sulcus (AIP), a dorsal-stream area implicated in the visual control of grasping. These findings provide additional support for the idea that visual perception and the visual control of action depend on separate visual pathways in the cerebral cortex, and confirm the respective roles of the ventral and dorsal visual streams in these functions.