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Schizophrenia Bulletin Advance Access originally published online on September 8, 2009
Schizophrenia Bulletin 2009 35(6):1108-1116; doi:10.1093/schbul/sbp090
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© The Author 2009. Published by Oxford University Press on behalf of the Maryland Psychiatric Research Center. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org.

Schizophrenia Patients Show Deficits in Shifts of Attention to Different Levels of Global-Local Stimuli: Evidence for Magnocellular Dysfunction

Michael J. Coleman2, Laurie Cestnick3, Olga Krastoshevsky2, Verena Krause2, Zhuying Huang4, Nancy R. Mendell5 and Deborah L. Levy1,2
2 Psychology Research Laboratory, McLean Hospital, 115 Mill Street, Belmont, MA 02478
3 Department of Psychiatry, Harvard Medical School, Boston, MA 02215
4 Department of Epidemiology, UT M.D. Anderson Cancer Center, Houston, TX 77030
5 Department of Applied Math and Statistics, Stony Brook University, Stony Brook, NY 11794

1 To whom correspondence should be addressed; tel: 617-855-2854; fax: 617-855-2778; e-mail: dlevy{at}mclean.harvard.edu

Abnormalities of attention and visual perception are well documented in schizophrenia. The global-local task is a measure of attention and perceptual organization that utilizes visual stimuli comprised of large letters (global level) made up of smaller letters (local level). Subjects identify target letters appearing at either the global or local level of the stimulus. In this study, we used a version of the global-local task specifically designed to examine lateralized hemispheric processing and attention shifting in 30 schizophrenia patients and 24 normal controls. Global-local stimuli were presented in couplets (consecutive pairs). Reaction time for the second target in a couplet was compared under conditions in which the target remained at the same level (global-global, local-local) and when the target changed levels (global-local, local-global). Level-specific priming (ie, global to global and local to local) and the local-to-global level shift were similar in both groups. Schizophrenia patients were significantly slower, however, shifting attention from the global to the local level. These results implicate an impairment in shifting attentional resources from predominantly right lateralized magnocellular/dorsal stream processing of global targets to predominantly left lateralized parvocellular/ventral stream processing of local targets. Local interference effects in global processing provide further support for impaired magnocellular processing in schizophrenia patients.

Keywords: magnocellular / parvocellular / global-local / schizophrenia / dorsal visual stream / ventral visual stream


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