The goal of this research is to characterize the nature of the internal representations that underlie the experience of visual mental imagery. By characterizing the brain areas that underlie imagery, the proposed research will provide insights into the possible consequences of stroke on a large variety of mental functions. The research is specifically designed to resolve contradictory results that have been reported by the Orsay positron emission tomography (PET) group and the Harvard/ Massachusetts General Hospital group. The Harvard group (as well as five others) has found that low-level visual areas 17 and/or 18 are activated during visual imagery, whereas the Orsay PET group (as well as one other) has not found such activation. In the proposed research, they will conduct two fMRI experiments to test three hypotheses regarding the disparity in findings. They will investigate whether the disparity is due to a difference in the resolution of the stimuli that are visualized, the difference between performing spatial task and visualizing the surface properties of objects, or simply individual difference.