Gregory R, Kroliczak G, Heard P, Goodale M, 2004, "Unmasking the two streams" Perception 33 ECVP Abstract Supplement
Unmasking the two streams
R Gregory, G Kroliczak, P Heard, M Goodale
We tested the suggestion that there are two separate visual streams in the human cerebral cortex: a ventral stream providing conscious perceptual information for cognitive operations including planning actions, and an evolutionarily older dorsal stream for rapid simple motor acts, not necessarily conscious. We depth-reversed cognitive visual space, with the hollow-face illusion, which is a large and stable cognitive (knowledge-based) effect. Participants 'flicked' targets on the hollow mask seen in reversed depth (recorded with 'Optotrack'). We found that for fast flicks -- initiating the ancient ventral system -- the fingers directed at the real locations; for slow pointing or tracing, they followed the illusory apparently convex face. So the same visual stimulus can result in opposite effects for conscious perception and rapid action; as expected for the 'two streams' concept, but otherwise surprising.
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