| Abstract No.: | C-D3134 |
| Country: | Canada |
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| Title: | NO MCCOLLOUGH EFFECT IN A PATIENT WITH CEREBRAL ACHROMATOPSIA BUT SPARED V1 |
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| Authors/Affiliations: | 2 Caitlin Mullin*; 1 Jean-François Démonet ; 2 Jennifer Steeves;
1 INSERM U455 Hôpital Purpan, Toulouse, France; 2 York University - Center for Vision Research, Toronto, ON, Canada
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| Content: | Background/Objective: The McCollough effect is a colour aftereffect contingent on pattern orientation. It has been extensively studied and historically has been thought to be mediated by primary visual cortex. However, more recent neuroimaging data has shown left V4 is involved in the induction of the McCollough 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 colour discrimination ability for highly saturated colours, albeit likely subconscious (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.
Materials & Methods: 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.
Results: 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. Control participants showed the greatest improvement in oblique grating orientation discrimination post-adaptation because their discrimination judgments became a colour discrimination based on the aftereffect colours for the oblique patterns rather than the more difficult orientation discrimination task. The patient, however, did not show improvement specifically on the oblique orientation discrimination.
Conclusions: This suggests that the original hypothesis of the McCollough effect depending solely on neural mechanism at an early stage of the primary visual pathway is incorrect. V1 must be connected to higher cortical colour areas to drive conscious perception of McCollough adaptation.
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