Low priority items are held in visual working memory: Evidence from flexible allocation in a two-alternative forced choice (2AFC) paradigm

Visual working memory (VWM) is characterized as extremely capacity limited. This finding is supported by the dramatic decline in change detection performance beyond a small number of items, as well as the observation of flat distributions of error in delayed-estimation tasks. However, continuous resource models predict that small amounts of memory resources can be distributed to items at the expense of memory resolution (and thus low response precision). These low-resolution representations should have nearly flat error distributions that could be indistinguishable from uniform guessing distributions. The current study intermixed continuous response and two-alternative forced choice (2AFC) trials to examine whether these low-precision items could produce above-chance performance, consistent with them being held in memory. Memory resource allocation was manipulated by varying the probability of an item being probed at recall, and memory sensitivity was manipulated by the size of the discrimination of the two alternative colors. Accuracy on the 2AFC trials was sensitive to both discrimination difficulty and probe probability manipulations. As well, response time was longer as probe probability decreased, and task difficulty increased, consistent with predictions of noisy memory representations. Critically, above chance performance was found in the lowest probe probability condition (10% probe probability, equivalent to an item load of 10) suggesting that this condition had low-resolution memory representations rather than no memory representations. These findings are consistent with the predictions of continuous resource models and applications of signal detection models of VWM.