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Sean R O’Bryan, Anto Jude Mohan, Hao Nguyen, Tyler Davis, Miranda Scolari; Category learning enhances visual perception at the boundary. Journal of Vision 2019;19(10):28c. doi: https://doi.org/10.1167/19.10.28c.
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Research suggests that category learning can warp visual perception, such that learned category boundaries stretch the psychological distance along relevant stimulus dimensions to facilitate successful categorization. We hypothesized that this perceptual warping may result from a representational sharpening of underlying sensory populations tuned to the category boundary. Furthermore, we expected such sharpening to occur largely during active learning of new categories. To test this hypothesis, we intermittently presented subjects with an orientation discrimination task where they reported the directional offset between two sequentially-presented gratings, while they were primarily engaged in an orthogonal categorization learning task. Subjects were pseudo-randomly assigned to one of eight boundary pairs within orientation space (n = 72) or a midpoint boundary within spatial frequency space (n = 69) for the categorization task. All subjects encountered randomly interleaved categorization (category A or B?) and orientation discrimination (rotated left or right?) trials; critically, all visual stimuli were physically matched between conditions. Perceptual discrimination performance was assessed for each of 36 possible reference orientations (0-175 degrees). Subjects were well-matched on categorization performance between orientation and spatial frequency conditions. To compare perceptual discrimination results between groups according to distance from the category boundary, we assigned arbitrary orientation boundaries to spatial frequency learners to match the distribution of the orientation group. Moreover, we contrasted subjects who successfully learned the orientation rule with those who failed to learn the rule. Our results revealed significantly greater performance among successful learners in the orientation group only for stimuli near the category boundary (0° and 5°) when compared to both spatial frequency learners and orientation non-learners. These results suggest that category learning temporarily enhances visual perception along dimensions relevant to categorization decisions, with the most prominent effects occurring at or near the category boundaries.
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