On 3 Mar 2005, [EMAIL PROTECTED] wrote: > I had a student ask me a question in class the other night regarding > split-brain patients. Does visual information go to both hemispheres?
I know it's late to be contributing to this thread, but I'm just now catching up on my e-mail backlog, and it seems to me that there's one point that wasn't mentioned in this interesting discussion. True, targets presented in the right visual field project to the left visual cortex, and vice versa. However, Sperry and probably all later researchers believed that input from the fovea had special representation with the visual cortex of both hemispheres. This caused a problem for presenting visual information restricted to one hemisphere, because a subject would automatically turn his/her eyes and head, causing the object to fall on the fovea. So special, sometimes elaborate techniques were used to prevent this. The most common was to flash the visual information tachistoscopically from one of the visual fields. Eye movements would be too slow to react, and so foveal input would be avoided. So the complete answer to the question would be that yes, visual information normally (in a non-testing situation) would go to both hemispheres of a split-brain patient. However, reseachers testing split-brain subjects routinely used tachistoscopic presentation to prevent this. But restricting visual information to targets flashed outside the fovea severely limited what they could present visually. Of course, if the researcher cited by Christopher Lovelace in his post is right, and the fovea actually does not have bilateral representation, then all of that fussing would have been unnecessary. That would certainly be ironic.It would be interesting to go back to the original studies of Sperry to see whether he provided empirical evidence that tachistoscopic presentation was essential for localisation of visual input to one hemisphere. Stephen ___________________________________________________ Stephen L. Black, Ph.D. tel: (819) 822-9600 ext 2470 Department of Psychology fax: (819) 822-9661 Bishop's University e-mail: [EMAIL PROTECTED] Lennoxville, QC J1M 1Z7 Canada Dept web page at http://www.ubishops.ca/ccc/div/soc/psy TIPS discussion list for psychology teachers at http://faculty.frostburg.edu/psyc/southerly/tips/index.htm _______________________________________________ --- You are currently subscribed to tips as: [email protected] To unsubscribe send a blank email to [EMAIL PROTECTED]
