Memory load modulates the role of perception in category effects in visual working memory

The origin of category effects in visual working memory (VWM) - whether they stem from perceptual factors - remains debated. The present study adopted an individual-differences approach to investigate how the magnitude of category effects relates to perceptual versus memory factors, as indexed by discrimination thresholds. Eighty participants completed two threshold tasks: one perceptual color discrimination task where two color patches were presented simultaneously, and one memory color discrimination task where patches were presented sequentially. They also performed a delayed estimation task, the performance of which was decomposed into categorical and continuous memory components. Results revealed that the strength of category effects was significantly larger under set size 3 compared to set size 1. Hierarchical regression analyses showed that both perception discrimination thresholds and memory discrimination thresholds uniquely predicted the strength of category effects when memory set size was 1, with higher thresholds associated with stronger category effects. However, when memory set size increased to 3, only memory discrimination thresholds uniquely predicted the strength of category effects, while its relationship with perceptual discrimination thresholds disappeared. These findings suggest that, when memory load was only one item, category effects may be partly contributed by perceptual factors. However, under higher memory loads, no reliable association was observed between perceptual factors and category effects. These findings suggest that memory load could modulate the relative contribution of perceptual and memory factors to category effects in visual working memory. OPEN PRACTICES STATEMENT: The trial-level data and experiment code for this study are publicly available at: https://osf.io/j5n7v/?view_only=8ffc5785136d4775be177929d18b01e1 . The experiment was not preregistered.