Probing bidirectional serial dependence in an N-back orientation estimation task

Vision is continuously shaped by a phenomenon known as serial dependence, wherein the estimation of stimulus features, such as orientation, is systematically biased by past visual input. This bias is believed to leverage the temporal autocorrelation in visual scenes, enhancing perceptual stability and sensitivity to change. To harness the full potential of temporal continuity, observers should consider not only the preceding stimulus but also the following one, when estimating a remembered stimulus feature embedded in a sequence of stimuli. Here, we used an N-back orientation estimation task to investigate whether serial dependence extends to memorized stimuli, with the preceding and/or following stimuli inducing the effect. Subjects were presented with a sequence of randomly oriented Gabor stimuli. The sequence terminated with a constant hazard rate, prompting subjects to recall the orientation of the 1-back stimulus (i.e., the target). Therefore, subjects had to keep in mind both the target and the following stimuli when prompted to recall the target. A probabilistic mixture model was employed to quantify contributions of different sources of error, excluding trials where subjects mistakenly reported the preceding or following stimulus instead of the target. Results revealed a highly consistent pattern of repulsive bias in the forward direction (preceding stimulus biases target estimation) and a weak trend of repulsive bias in the backward direction (following stimulus biases target estimation). Intriguingly, the strength of the repulsive bias was more pronounced for the preceding stimulus, despite the more recent presentation of the following stimulus, which would intuitively be expected to have a stronger working memory trace. These results underscore that our memory of visual scenes is influenced by both preceding and following stimuli, with the bias in forward direction prevailing in bidirectional serial dependence. Overall, our findings contribute to a deeper understanding of mechanisms underlying serial dependence in visual working memory.