Studies of change detection have shown that changing the task-irrelevant features of remembered objects impairs change detection for task-relevant features, a phenomenon known as the irrelevant change effect. Although this effect is pronounced at short study-test intervals, it is eliminated at longer delays. This has prompted the proposal that although all features of attended objects are initially stored together in visual working memory (VWM), top-down control can be used to suppress task-irrelevant features over time. The present study reports the results of three experiments aimed at testing the top-down suppression hypothesis. Experiments 1 and 2 tested whether the magnitude or time course of the irrelevant change effect was affected by the concurrent performance of a demanding executive load task (counting backwards by threes). Contrary to the top-down suppression view, the decreased availability of executive resources did not prolong the duration of the irrelevant change effect in either experiment, as would be expected if these resources were necessary to actively suppress task-irrelevant features. Experiment 3 showed that a visual pattern mask eliminates the irrelevant change effect and suggests that the source of the effect may lie in the use a high-resolution, sensory memory representation to match the memory and test displays when no task-irrelevant feature changes are present. These results suggest that the dissipation of the irrelevant change effect over time likely does not depend on the use of top-down control and raises questions about what can be inferred about the nature of storage in VWM from studies of this effect.

Maintaining visual working memory (VWM) representations recruits a network of brain regions, including the frontal, posterior parietal, and occipital cortices; however, it is unclear to what extent the occipital cortex is engaged in VWM after sensory encoding is completed. Noninvasive brain stimulation data show that stimulation of this region can affect working memory (WM) during the early consolidation time period, but it remains unclear whether it does so by influencing the number of items that are stored or their precision. In this study, we investigated whether single-pulse transcranial magnetic stimulation (spTMS) to the occipital cortex during VWM consolidation affects the quantity or quality of VWM representations. In three experiments, we disrupted VWM consolidation with either a visual mask or spTMS to retinotopic early visual cortex. We found robust masking effects on the quantity of VWM representations up to 200 msec poststimulus offset and smaller, more variable effects on WM quality. Similarly, spTMS decreased the quantity of VWM representations, but only when it was applied immediately following stimulus offset. Like visual masks, spTMS also produced small and variable effects on WM precision. The disruptive effects of both masks and TMS were greatly reduced or entirely absent within 200 msec of stimulus offset. However, there was a reduction in swap rate across all time intervals, which may indicate a sustained role of the early visual cortex in maintaining spatial information.

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The ability to remember feature bindings is an important measure of the ability to maintain objects in working memory (WM). In this study, we investigated whether both object- and feature-based representations are maintained in WM. Specifically, we tested the hypotheses that retaining a greater number of feature representations (i.e., both as individual features and bound representations) results in a more robust representation of individual features than of feature bindings, and that retrieving information from long-term memory (LTM) into WM would cause a greater disruption to feature bindings. In four experiments, we examined the effects of retrieving a word from LTM on shape and color-shape binding change detection performance. We found that binding changes were more difficult to detect than individual-feature changes overall, but that the cost of retrieving a word from LTM was the same for both individual-feature and binding changes.