Serial dependence is absent at the time of perception but increases in visual working memory

Recent experiments have shown that visual cognition blends current visual input with that from the recent past to guide ongoing decision making. This serial dependence is tuned to the similarity between consecutive stimuli and appears to exploit the temporal autocorrelation normally present in visual scenes to promote perceptual stability. While these benefits have been assumed, evidence that serial dependence directly alters stimulus perception has been limited. In the present study, we parametrically vary the delay between stimulus and response in a spatial delayed response task to explore the trajectory of serial dependence from the moment of perception into post-perceptual visual working memory. We find that behavioral responses made immediately after viewing a stimulus show evidence of adaptation, but not attractive serial dependence. Only as the memory period lengthens is a blending of past and present information apparent in behavior, reaching its maximum with a memory delay of six seconds. These results dovetail with other recent findings to bolster the interpretation that serial dependence is a phenomenon of mnemonic rather than perceptual processes. We also demonstrate that when leading mathematical models of visual working memory are adjusted to account for this trial-history effect, their fit to behavioral data is substantially improved.