fined form without deficits in the detection of motion or
the perception of the direction of motion [64˙].An even more difficult set of problems concerns the role
of attention and consciousness in the two streams of processing (for a discussion of these issues, see [14,15˙˙]).
Are the attentional mechanisms that operate during perception different from those that operate during the performance of skilled visuomotor acts? What is the nature
of the distinction between 'conscious' perceptual experience and the apparently 'automatic' control of action?
What are the neural substrates for these differences?
While the answers to these and related questions will
not come easily, the re-casting of the division of labor
between the ventral and dorsal streams into a distinction
between perception and action may provide a useful theoretical framework for exploring the role of attention and
consciousness in visual processing.
ConclusionsIn summary, there is a good deal of electrophysiological and behavioral evidence supporting the idea that
two very different sets of transformations are carried
out in the primate cerebral cortex and the characteristics of these transformations reflect the requirements
of the different output systems that they serve. The two
streams of visual processing that emanate from primary
visual cortex appear to reflect this distinction: the ventral stream delivers the visual representations underlying
long-term knowledge of objects and events in the world,
and the dorsal stream, which utilizes the instantaneous
and egocentric features of objects, mediates the on-line
visual control of goal-directed actions.
AcknowledgementsResearch in the author's laboratory is supported by a grant from the Medical Research Council of Canada.
References and recommended readingPapers of particular interest, published within the annual period of
review, have been highlighted as:
|• ||• of special interest|
|• ||•• of outstanding interest|
This study describes experiments showing that selective inactivation of
either the M or P pathway at the level of the LGNd can affect the responsivity of cells in V4. These results indicate that the both the M and
the P pathways make significant contributions to the ventral stream.
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Both this paper and the earlier version by Goodale and Milner 
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Questia, a part of Gale, Cengage Learning. www.questia.com
Book title: Origins:Brain and Self Organization.
Contributors: Karl Pribram - Editor.
Publisher: Lawrence Erlbaum Associates.
Place of publication: Hillsdale, NJ.
Publication year: 1994.
Page number: 590.
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