Abstract
It is well-established that visual working memory (VWM) and perception interact to influence behavior. For example, studies have shown that novel visual input can retroactively distort VWM representations by inducing systematic attraction biases. The size of these biases may be determined automatically by the extent to which features shared between visual input and VWM content overlap with one another. However, it may also be the case that explicitly comparing VWM content to visual input plays a causal role in modulating these observed biases. Here, we tested the hypothesis that explicitly comparing a VWM representation to a visual input causally amplifies memory biases that occur naturally as a result of overlapping visual features. In each trial of two separate experiments, participants first encoded a target visual item (i.e., color or shape) into VWM in anticipation of a continuous report that followed a blank delay interval. On a subset of trials, participants were presented a novel probe item during the blank delay and were instructed to compare it to the target held in VWM. The memory biases observed in this task were then compared to those observed in a separate task where the same participants ignored the probe (Experiment 1) or encoded the probe into VWM alongside the target (Experiment 2). We found that individuals reported larger attraction biases in the target item following explicit comparisons than when they ignored or remembered the probe. A follow-up analysis revealed that memory biases were amplified when participants judged the probe to be similar—but not dissimilar—to the target item. This pattern persisted even after the distance between the target and probe items in the stimulus space was matched across trials. Taken together, these findings demonstrate that explicit perceptual comparisons causally modulate VWM biases above and beyond the effects determined by shared featural overlap.