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Luis D Ramirez, Julia Schwartz, Ilona Bloem, Sam Ling, Melissa M Kibbe; Spatial location does not elicit normalization in visual memory. Journal of Vision 2019;19(10):245. doi: https://doi.org/10.1167/19.10.245.
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Perception and visual memory are fundamental to cognition, and yet the neural correlates that make them unique have yet to be fully understood. Recent work has found that visual memories bypass normalization, a canonical computation that commonly occurs in perception (Bloem et al., 2018). Here, we examined whether having an item tied to a contrast and spatial location elicits normalization in visual memory. Given that spatial location is a fundamental representation in retinotopic space, we reasoned that this task would encourage a high-fidelity representation of the remembered stimulus that would be potentially more prone to normalization. Building off of Bloem et al., 2018, our surround suppression paradigm consisted of a method-of-adjustment task in which participants (n=10) replicated the location and contrast of a central stimulus, which was enveloped by a full contrast surround stimulus presented simultaneously with (perception condition), or sequentially from (visual memory condition), the central stimulus. To quantify normalization strength, these two conditions were compared to an absent surround condition. Participants reported both the location and perceived contrast for stimuli across five contrast levels (10%–75%), at various locations (0–359°) near the boundary of foveal vision (eccentricity=5°). After a delay-period, participants used a dial to replicate the location and contrast held in memory. While the precision of reports for both location and contrast were highly comparable between conditions, results show that normalization-driven suppression only emerged during perception, with only signs of minor facilitation in visual memory. In sum, this experiment further substantiates that visual memory and visual perception are distinct from each other: while visual memory may engage the same cortical areas as visual perception, its representations appear qualitatively distinct from true visual representations.
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