Research report Brain areas underlying visual mental imagery and visual perception: an fMRI study Giorgio Ganis a,b,c, * , William L. Thompson a , Stephen M. Kosslyn a,d a Department of Psychology, Harvard University, Cambridge, MA 02138, USA b Department of Radiology, Massachusetts General Hospital Martinos Center, Boston, MA 02114, USA c Harvard Medical School, Boston, MA 02115, USA d Department of Neurology, Massachusetts General Hospital, Boston, MA 02114, USA Accepted 15 February 2004 Available online 30 April 2004 Abstract We used functional magnetic resonance imaging (fMRI) to assess the maximal degree of shared neural processing in visual mental imagery and visual perception. Participants either visualized or saw faint drawings of simple objects, and then judged specific aspects of the drawings (which could only be evaluated properly if they used the correct stimulus). The results document that visual imagery and visual perception draw on most of the same neural machinery. However, although the vast majority of activated voxels were activated during both conditions, the spatial overlap was neither complete nor uniform; the overlap was much more pronounced in frontal and parietal regions than in temporal and occipital regions. This finding may indicate that cognitive control processes function comparably in both imagery and perception, whereas at least some sensory processes may be engaged differently by visual imagery and perception. D 2004 Elsevier B.V. All rights reserved. Theme: Neural Basis of Behavior Topic: Cognition Keywords: Visual cognition; Visual imagery; Cognitive neuroscience; fMRI; Cognitive control processes 1. Introduction During visual mental imagery, perceptual information is retrieved from long-term memory, resulting in the subjective impression of ‘‘seeing with the mind’s eye’’. The phenom- enological similarity between visual imagery and visual perception has been noted at least since the time of the Greek philosophers. Plato, for instance, describes mental imagery by using the metaphor of a mental artist painting pictures in the soul (Philebus 39c). At least since the 1960s, after the cognitive revolution that followed the behaviorist years, ‘analog’ theories posited that visual mental imagery and visual perception share numerous common representa- tions and processes. This hypothesis led to many behavioral predictions, which typically bore fruit. For example, visual imagery selectively interferes with visual perception more than auditory perception (and vice versa [8,54]), more time is required to scan greater distances across visualized objects [9,34], and eye movements during imagery are similar to those made during perception [42]. If we assume that cognitive processes arise from specific patterns of brain activation, then the hypothesis that like- modality imagery and perception share many common representations and processes can also be tested using neuroimaging. Specifically, this view leads us to predict substantial overlap in neural activation during visual mental imagery and visual perception. To date, only one study [39] has been designed specif- ically to (1) compare directly the pattern of brain activation during visual mental imagery and visual perception across most of the brain, and (2) quantify the degree of overlap. This study was designed to compare stimuli and tasks that differed on the surface but were hypothesized to share 0926-6410/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cogbrainres.2004.02.012 * Corresponding author. Department of Psychology, Harvard Univer- sity, 33 Kirkland Street, Cambridge, MA 02138, USA. Tel.: +1-617-495- 3569; fax: +1-617-496-3112. E-mail address: ganis@wjh.harvard.edu (G. Ganis). www.elsevier.com/locate/cogbrainres Cognitive Brain Research 20 (2004) 226 – 241