Reactivation of prior responses drives serial dependence and stabilizes working memory representations

Serial dependence has shown seemingly contradictory effects on visual perception and working memory. While serial dependence promotes perpetual and mnemonic stability, it biases behavioral reports towards prior information. The neural mechanisms that drive both biasing and adaptive stabilizing effects are not well understood. We proposed and tested a reactivation and integration mechanism that can account for these contradictory effects. We used multivariate pattern analyses of EEG data (26 human participants, 17 females, 9 males) to examine the reactivation of prior reported orientation during the delay period of a visual working memory task. The reactivation strength of prior reports, but not prior sensory items, was predictive of the magnitude of serial-dependency biases. These reactivated representations integrated with the representation of the current memory item and improved the ability to decode the current contents of memory. Overall, our data provide convergent evidence suggesting that prior reports in a visual working memory task are reactivated on the subsequent trial and become integrated with current memory representations. This similarity-dependent reactivation mechanism drives both report biasing and stabilization effects attributed to serial-dependence in working memory. Significance Statement A primary objective of working memory is to differentiate the present from the past. However, in a continuous visual experience, recent past information often remains relevant for processing subsequent information. How can working memory leverage relevant past information to aid perception and memory while avoiding unwanted influence from irrelevant past information? Here, we show that maintaining new information in working memory can selectively reactivate and assimilate similar information from the recent past. This reactivation biases memory for present items towards the past, which may not always be desirable, but it also enhances the fidelity and precision of these memories, which is certainly an adaptive feature.