A Discrete Component in Visual Working Memory Encoding

Working memory (WM) is a central cognitive bottleneck, which has primarily been attributed to its well-known storage limit. However, relatively little is known about the processing limit during the initial memory encoding stage, which may also constrain various cognitive processes. The present study introduces a novel method using dynamic stimulus presentation and hierarchical Bayesian modeling to quantitatively estimate visual WM encoding speed. Participants performed a delayed-estimation task with two memory items continuously changing color hues in perceptually unnoticeable steps. Across three experiments, the recall errors systematically shifted toward the direction of color change, providing a proxy measure of encoding speed. Importantly, the observed shifts were best characterized by a temporal lag during the encoding of different items, supported by a mixture of two distributions with credibly distinct encoding times. A supplementary model-free analysis further confirmed the discrete encoding component in visual WM for multiple items. These findings shed light on the temporal dynamics of WM encoding processes. Public Significance Statement Working memory (WM) can shape our coherent perception of the world by updating information over time. Despite this ability, the rate at which sensory experiences are encoded into memory is limited. The present study explored how two dynamically changing, but unnoticeable to the observers, colors are encoded into WM. We found that memories for these colors are lagging in time within the spectrum of color changes, providing a temporal metric for assessing the temporal dynamics of memory encoding. Notably, a temporal gap emerged between the two remembered colors, with one being reliably encoded earlier than the other. Our study highlights that multiple objects in the continuous physical world are not captured simultaneously in mind all together but with a temporally discrete gap in between.