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Scott A. Beardsley, Lucia M. Vaina; Improved complex motion discrimination in a patient with a bilateral occipital lobe lesion. Journal of Vision 2004;4(8):855. doi: 10.1167/4.8.855.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. We use spatial summation in two complex motions tasks to quantify functional improvement in patient WB, with a bilateral posterior cerebral artery infarct involving the medial occipital lobes. WB exhibited a large scotoma with central 10 deg sparing around the fovea and extending into the lower right quadrant of the visual field. Methods. Discrimination thresholds for speed and coherence were obtained to quantify improvements in spatial summation over time. In a 2TAFC central fixation task radial or circular RDKs were presented within a 24 deg aperture (central 4 deg removed). In speed discrimination, spatial summation was examined as a function of the number and width of signal sectors for three levels of motion noise (50, 75, and 100% coherence). In the motion pattern coherence task, observers discriminated opposing radial motions as a function of a masking motion noise. Spatial summation was quantified as a function of width for a single signal sector centered within WB's spared lower right visual field. Results. WB remained impaired on speed discrimination in his spared visual field, but thresholds for specific motion patterns improved significantly for multi-sector stimuli containing as little as 25% signal area (p<0.05). For expanding motions in particular, full-field thresholds (∼7±2%) approached those of normal observers (5±1%). In contrast WB's ability to discriminate radial direction in the motion coherence task was normal across his spared visual field. Contrast sensitivity was also normal. Conclusion. Motion pattern specific improvement in WB's speed discrimination suggests functional recovery in the motion pattern mechanisms previously shown to mediate these psychophysical tasks. Together with the differential impairment in WB's ability to discriminate speed vs. coherence, we suggest that improved motion pattern discrimination results from the recovery of local speed mechanisms, distinct from local direction mechanisms, that feed into them.
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