Acta Psychologica 107 (2001) 43±68
De®ning the cortical visual systems:
``What'', ``Where'', and ``How''
Sarah H. Creem a,*, Dennis R. Prott b
a Department of Psychology, University of Utah, 380 S. 1530 E., Rm 502, Salt Lake City, UT 84112-0251,
b University of Virginia, VA, USA
Received 5 April 2000; received in revised form 19 October 2000; accepted 25 October 2000
The visual system historically has been de®ned as consisting of at least two broad sub-
systems subserving object and spatial vision. These visual processing streams have been or-
ganized both structurally as two distinct pathways in the brain, and functionally for the types
of tasks that they mediate. The classic de®nition by Ungerleider and Mishkin labeled a ventral
``what'' stream to process object information and a dorsal ``where'' stream to process spatial
information. More recently, Goodale and Milner rede®ned the two visual systems with a focus
on the dierent ways in which visual information is transformed for dierent goals. They
relabeled the dorsal stream as a ``how'' system for transforming visual information using an
egocentric frame of reference in preparation for direct action. This paper reviews recent re-
search from psychophysics, neurophysiology, neuropsychology and neuroimaging to de®ne
the roles of the ventral and dorsal visual processing streams. We discuss a possible solution
that allows for both ``where'' and ``how'' systems that are functionally and structurally or-
ganized within the posterior parietal lobe. Ó 2001 Elsevier Science B.V. All rights reserved.
PsycINFO classi®cation: 2323; 2340; 2520; 3297
Keywords: Cognitive neuroscience; Parietal lobe; Perception and action; Spatial processing;
Visual processing; Visuomotor system
*Corresponding author. Tel.: +1-801-581-5045; fax: +1-801-581-5841.
E-mail address: firstname.lastname@example.org (S.H. Creem).
0001-6918/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved.
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