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Brian Barton, Alyssa Brewer; Visual Working Memory Capacity in Retinotopic Cortex: Number, Resolution, and Population Receptive Fields. Journal of Vision 2010;10(7):729. doi: 10.1167/10.7.729.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: Visual working memory (VWM) capacity has been shown to be limited by the number of items one can hold in memory and the resolution at which those items are represented. The number limit appears to be subserved by cortex in inferior interparietal sulcus (IPS), while the resolution limit seems to be subserved by superior IPS and part of the lateral occipital complex (LOC). Visual field maps have recently been discovered in IPS and LOC, and some or all of the regions involved in VWM capacity limits may lie in these visual field maps, which may have functional consequences for VWM capacity limits. Methods: We measured angular and eccentric retinotopic organization and population receptive fields across visual cortex using fMRI. Retinotopic stimuli consisted of black and white, drifting checkerboards 11° in radius comprising wedges, rings, and/or bars. A change detection task with set sizes 1, 2, 4 or 8 was performed using fMRI, with locations of stimuli controlled such that they were in the shape of a ring or wedge, to directly measure angular and eccentric VWM organization. The stimuli consist of colored squares (6 possible colors) or shaded cubes (controlled for spatial frequency, in 6 colors with 6 shading patterns, with low-similarity changes between colors and high-similarity changes between shading patterns) that subtend roughly 1° of visual angle. Results/Discussion: We present the location of functionally defined regions underlying VWM capacity limits and whether some or all fall into visual field maps. The change detection tasks replicate previous studies showing that we maintain just as many complex objects as simple objects, but at limited resolution. We present the first measurements of population receptive fields in IPS visual field maps, and analyze the number limit and mnemonic resolution for simple and complex objects as a function of population receptive fields.
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