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J. Brendan Ritchie, Susan Wardle, Anina Rich, Stuart Graham, Mark Williams; Decoding Feedback to the Lesion Projection Zone of V1 in Individuals with Glaucoma. Journal of Vision 2015;15(12):1252. doi: 10.1167/15.12.1252.
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© ARVO (1962-2015); The Authors (2016-present)
Feedback is a fundamental organising principle of the visual system. Using fMRI decoding methods, Jehee, Brady and Tong (2011) demonstrated that orientation information about an attended stimulus could be decoded in regions of V1 that were not directly activated by that stimulus. Their results have been interpreted as evidence for attention-driven feedback to V1. In normally sighted individuals, however, we cannot completely isolate feedback signals from activity due to feedforward processing. Individuals with monocular glaucoma present an opportunity to investigate feedback signals in the absence of direct visual input to the cortical region. We tested whether information about the orientation of a visible stimulus was present in the portion of visual cortex reflecting the scotoma location (lesion projection zone; LPZ) in individuals with glaucoma. We reasoned that if there is feedback to other regions of V1 when a stimulus is attended, then the same feedback could be observed in the LPZ of V1. We recruited subjects with monocular glaucoma of the right eye, and identified a scotopic quadrant and a relatively unimpaired quadrant of the visual field for each subject. Subject specific localization of the four quadrants of V1 was carried out using functional retinotopy (binocular viewing) and anatomical markers. Oriented gratings (3.5° radius, centered 5° from fixation) were presented (monocular viewing) in the visible quadrant. Subjects performed an orientation discrimination task while maintaining central fixation and covertly attending to the stimuli. Linear classifiers were then trained to predict stimulus orientation using neural data from each of the four quadrant regions. Although the decoding results were variable between subjects, for a subset of participants, stimulus orientation was indeed decodable from the LPZ quadrant. Our results provide proof of concept that feedback signals can be preserved in the absence of activity from direct visual input.
Meeting abstract presented at VSS 2015
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