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Caitlin Mullin, Jean-François Démonet, Jennifer K. E. Steeves; No McCollough effect in a patient with cerebral achromatopsia but spared V1. Journal of Vision 2008;8(6):489. doi: 10.1167/8.6.489.
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The McCollough effect is a colour aftereffect contingent on pattern orientation. It has been extensively studied and, historically it has been thought to be mediated by the primary visual cortex (V1). However, more recent neuroimaging data has shown left V4 is involved in the induction of theMcCollough effect (Morita et al, 2004). To determine whether the primary visual cortex is sufficient to drive the McCollough effect or whether connections to higher cortical colour areas are necessary, we tested a patient with acquired brain damage to ventrotemporal cortex but spared V1 in one hemisphere (SB) and controls. Patient SB lacks orientation discrimination and has cerebral achromatopsia but has been shown to have some subconscious colour discrimination ability forhighly saturated colours (Lê et al., 2002). A similar experiment was conducted with Patient DF who has similar deficits but shows conscious colour discrimination (Humphrey et al., 1991). Here we asked whether this effect could be induced in a patient without conscious colour abilities. Participants performed a 2AFC same/different orientation discrimination task for oblique pairs or vertical/horizontal pairs of square wave gratings. Participants then adapted to highly saturated red and green oblique gratings for 20 minutes before re-testing on the orientation discrimination task. Control participants were better at discrimination of horizontal and vertical gratings compared to obliquely oriented gratings in the pre-adaptation period—this is the well-known Oblique effect. Following adaptation, control participants showed the greatest improvement for oblique compared to horizontal/vertical grating discrimination. Post-adaptation, the more difficult oblique orientation discrimination judgments were a simpler colour discrimination judgement as a result of McCollough adaptation. SB, however, did not show improvement specifically for oblique gratings. This suggests that V1 must be connected to higher cortical colour areas to drive McCollough adaptation.
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