The effect of abstract representation and response feedback on serial dependence in numerosity perception.

Serial dependence entails an attractive bias based on the recent history of stimulation, making the current stimulus appear more similar to the preceding one. Although serial dependence is ubiquitous in perception, its nature and mechanisms remain unclear. Here, in two independent experiments, we test the hypothesis that this bias originates from high-level processing stages at the level of abstract information processing (Exp. 1) or at the level of judgment (Exp. 2). In Experiment 1, serial dependence was induced by a task-irrelevant "inducer" stimulus in a numerosity discrimination task, similarly to previous studies. Importantly, in this experiment, the inducers were either arrays of dots similar to the task-relevant stimuli (e.g., 12 dots), or symbolic numbers (e.g., the numeral "12"). Both dots and symbol inducers successfully yielded attractive serial dependence biases, suggesting that abstract information about an image is sufficient to bias the perception of the current stimulus. In Experiment 2, participants received feedback about their responses in each trial of a numerosity estimation task, which was designed to assess whether providing external information about the accuracy of judgments would modulate serial dependence. Providing feedback significantly increased the attractive serial dependence effect, suggesting that external information at the level of judgment may modulate the weight of past perceptual information during the processing of the current image. Overall, our results support the idea that, although serial dependence may operate at a perceptual level, it originates from high-level processing stages at the level of abstract information processing and at the level of judgment.