Task-irrelevant motion information modulates working memory representations

Previous studies have shown that working memory (WM) influences perception at both behavioral and neural levels (Kang et al., 2011, D’Esposito & Postle, 2015). For example, holding orientation information from a random dot kinematogram (RDK) in working memory influences subsequent perceptual judgments. However, most studies only require memorizing a single feature; whether multi-feature information held in WM influences perceptual decision-making, and vice-versa, is not fully understood. In this study, we explored both questions by exploiting the “motion repulsion” effect (Marshak & Sekuler, 1979). Thirty-one participants were presented with sequences of three RDKs, where the first (RDK1) and third (RDK3) shared two out of three properties (orientation, speed, or dot density). The task required subjects to report the orientation of the second RDK (RDK2), and also report (and rate confidence for) the property that differed between RDK1 and RDK3. Importantly, an irrelevant feature for the task—RDK2’s speed—was systematically altered across three experiments (exp1: similar speed to RDK1, exp2: faster, exp3: slower). Here, we asked the following question: does manipulation of a task-irrelevant feature (RDK2’s speed) influence the working memory judgment about RDK1 and RDK3? Our findings revealed that the motion repulsion effect, a perceptual phenomenon, was consistently observed at previously-reported angles (30° and 60°), despite the increased cognitive load of our task, which required maintaining multiple features in WM. Notably, in the experiment with the slowest irrelevant speed (exp3), task performance was adversely affected compared to the other conditions. Additionally, a unique pattern of metacognitive sensitivity emerged in the experiment with increased irrelevant speed (exp2): participants exhibited a higher proportion of “low confidence” responses for both correct and incorrect trials. Overall, these results demonstrate that motion repulsion occurs even when multiple features are held in working memory, and reveal an influence of task-irrelevant perceptual information on WM judgments.