The time course of serial dependence: an interplay between perceptual decisions and task relevant representations

In serial dependence (SD), features of a present stimulus are judged as similar to previously presented ones. This bias is often explained by a continuity field (CF) in perception, combining similar stimuli in an extended region of space (∼ 15°) and time (∼15 seconds) to support non-retinotopic stabilisation across eye movements. We here question the existence of a CF in vision by focusing on its temporal properties. We investigated: 1) whether combining stimuli within the CF is mandatory and 2) whether SD is defined by the CF or by the number of previous stimuli. We presented sequences of low contrast Gabors in each trial and observers performed an orientation adjustment task. A sequence contained either 2, 3 or 4 Gabors separated by 12, 6 or 4 seconds, respectively. Participants were asked to reproduce the orientation of the last Gabor. Despite all the non-reported stimuli fell within the temporal window of the CF, we found only repulsive biases, i.e., the opposite of SD. Hence, the combination of visual features within the CF is not mandatory. Interestingly, we observed positive SD for the orientations reported one trial in the past, despite the interval could extend to the hypothetical limits of the CF (>15 seconds). Rather than supporting the existence of a CF, our results suggest that SD depends on the interplay between decisions and task-relevant representations. [This research was supported by funding from the Swiss National Science Foundation (grant no. 415 PZ00P1_179988 to DP). The funders had no role in the study design, data collection and analysis.]