Serial dependence to prior stimuli and past responses

Previous work on serial dependence has centered on whether attractive biases emerge during early sensory processing (Fisher & Whitney 2014, Cicchini et al., 2017) or are driven by decionsional or response production processes (Pascucci et al. 2019, Sadil et al. 2021, Sheehan & Serences, 2021). In Experiment 1 (n=13) we sought to isolate the effects of the stimulus on serial bias in a spatial delayed report task where the stimulus was visible on some trials and imagined on others. We found systematic attraction to the previous stimulus irrespective of stimulus visibility (p<.0005) suggesting that sensory processing is not necessary to induce attractive biases. However, on 1/3rd of trials the previous stimulus did not require a response (“drop trial”) but still induced an attractive bias (p<.05) suggesting that overt report is also not essential. Thus Experiment 1 suggests that neither sensory processing nor an explicit response is required to induce serial dependence. In Experiment 2 (n=20), we further disentangled contributions of stimulus and response by adding trials where subjects responded 180 degrees from the actual stimulus location (“flip-response”) or they responded to a new random location (“random response”). In this paradigm, we again found attractive serial biases regardless of whether the current or previous stimulus was visible (p’s <.001). However, attraction was stronger when the current stimulus was visible (p<.05), suggesting that both sensory and non-sensory components contribute. Critically, we found that responses were attracted to the previously responded-to location following both “flip-response” and “random-response” trials (p<.0001) but showed no residual attraction to the previously remembered location. Together these studies suggest that serial dependence simultaneously reflects contributions from stimulus processing, memory maintenance, and response production and argue against a unitary account.