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* Corresponding author 1 Equipe de Psychologie Cognitive 2 NFP - Neurosciences fonctionnelles et pathologies 3 Section of Neurobiology, Physiology and Behavior, Department of Ophthalmology 4 Cerveau et vision

Abstract : Recently developed psychophysical techniques permit the biasing of the processing of the stimulus by early visual channels so that responses reflect characteristics of either magno- or parvocellular pathways Pokorny & Smith, 1997. We used such techniques to test psychophysically whether the global magnocellular dysfunction reported in schizophrenia also affects early processes. Seven schizophrenic patients and 19 normal controls participated. The task was a four-alternative forced-choice luminance discrimination, using a 2 x 2 configuration of four 1-deg squares. Target luminance threshold was determined in three conditions: the stimulus, including the target, was pulsed for 17 ms pulse paradigm; the target was presented on a steady background of four squares steady paradigm, or the target was presented alone no background paradigm. We replicated previous results demonstrating magnocellular and parvocellular signatures in control participants. No evidence for an early magnocellular deficit could be detected as the thresholds of all schizophrenic observers were higher both in the steady paradigm presumed magnocellular mediation and in the pulse paradigm presumed parvocellular mediation. Magnocellular dysfunction, if present in schizophrenia, must concern more integrated processes, possibly at levels at which parvocellular and magnocellular paths interact.

Keywords : Psychophysics Magnocellular Parvocellular Schizophrenia

Autor: Sandrine Delord - Maria Giovanna Ducato - Delphine Pins - Frédéric Devinck - Pierre Thomas - Muriel Boucart - Kenneth Knoblauch



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