INTACT VISUAL-IMAGERY AND IMPAIRED VISUAL-PERCEPTION IN A PATIENT WITH VISUAL AGNOSIA

Although it is now well accepted that visual mental imagery and visual perception share common underlying mechanisms, there are several repo rts in which they are dissociated. Evidence for the separability of th ese processes is provided by a patient, C.K., who has a profound visua l object recognition deficit attributable to an impairment in grouping or segmenting visual images. Despite this perceptual deficit, C.K. wa s able to draw objects in considerable detail from memory, and his kno wledge of the visual appearance of objects was preserved on a variety of mental imagery tasks. Together with previous cases, these findings confirm the double dissociation between object recognition and percept ion. Interestingly, C.K. could also recognize newly constructed object s in his internal imagery. To accommodate these results, we propose a model in which imagery and perception are strongly associated but are also functionally specialized.