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Dissociable Neural Mechanisms for Capacity & Resolution in Visual Working Memory

23.553, Saturday, 17-May, 8:30 am - 12:30 pm, Pavilion
Session: Visual memory: Mechanisms and models

Marcus Cappiello1, Weizhen Xie1, Weiwei Zhang1; 1Psychology, University of California, Riverside

The capacity and resolution of visual working memory (VWM) representation reflect two independent sources of limits on working memory storage. The relationships between the two factors have been the subject of considerable controversy. According to the discrete slot model, VWM stores a limited set of discrete, fixed-resolution representations. A key prediction of this model is the dissociations of VWM capacity and resolution. In sharp contrast, the flexible resource model predicts a tradeoff between VWM capacity and resolution. That is, the amount of resources each representation gets can be flexibly varied so that either a larger number of coarse-grained representations or a smaller number of fine-grained representations can be retained in VWM. Previous research with behavioral approaches has demonstrated VWM capacity and resolution can be operationally defined and experimentally manipulated in independent manners, providing some support for the slot model. However, it becomes difficult to distinguish the two competing models with behavioral methods alone when multiple slots are averaged to represent a single memory item in order to boost resolution at the cost of capacity. The present study used non-invasive brain stimulation techniques to test whether there are dissociable and independent neural mechanisms for VWM capacity and resolution. In two experiments, VWM was tested in a color recall task in which observers attempted to retain several colors in VWM over a 1-s retention interval and then recalled one of them by clicking on a color wheel. In Experiment 1, bilateral transcranial Direct Current Stimulation (tDCS) over the anterior temporal lobes induced a virtual lesion in resolution with intact capacity. In Experiment 2, alpha-band transcranial Alternating Current Stimulation (tACS) over the posterior parietal cortex selectively enhanced capacity with intact resolution for ipsilateral stimuli compared to contralateral stimuli. Taken together, these results have demonstrated dissociable neural mechanisms for VWM capacity & resolution.

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