Irrelevant features of distractors in intervening visual search tasks cause active visual working memory interference - the more difficult the search task, the more interference it causes.

Visual working memory (VWM) content disrupts visual search performance when there is a singleton in the search array that is similar to the content in VWM, even when this singleton is task irrelevant. Typically, the memory-similar singleton captures attention, which results in slower search performance for memory-similar conditions compared to conditions where memory-similar content is absent. Recently, it has also been shown that VWM content may be affected when memory-similar stimuli are processed. Specifically, it appears that VWM representations bias toward memory-similar information that is processed but not memory-dissimilar information. Here, we test whether the bias caused by processing memory-similar information is an active interference process (growing with engagement with the memory-similar stimuli) or a passive interference process (indifferent to the engagement with memory-similar stimuli). To test this, observers were tasked with memorizing a single color followed by a search task. The search task was either easy or difficult, and the search items could either be memory-similar or memory-dissimilar. Critically, the target in the search task was defined by its shape, so the color of the search items was irrelevant to the search task. At the end of each trial, participants reported the color in memory using a continuous report color wheel. The results showed that VWM representations drifted towards the irrelevant color of the search items in the memory-similar conditions, and this effect was larger in the difficult search condition. The results provide evidence that VWM representations receive active interference from processing memory-similar stimuli.