Serial dependence in the perception of proportion

The influence of previously encountered stimuli on subsequent perceptual judgments is termed serial dependence. Serial dependence has been robustly demonstrated across a broad spectrum of visual features, ranging from low-level attributes, such as orientation and color, to high-level representations, including facial identity. To further understand this dependency, the present study investigated the presence of serial dependence in judgments of relative proportions within visual stimuli. Participants completed a two-alternative forced-choice (2AFC) task involving stimuli composed of two symbols. These symbols differed only in brightness in Experiment 1 and only in shape in Experiment 2. Participants were required to judge which symbol occupied the larger proportion. The results revealed a systematic bias in the participants responses. Specifically, Experiment 1 yielded a repulsive bias (negative serial dependence), where current judgments shifted away from the proportion observed in the preceding trial. Conversely, Experiment 2 exhibited an attractive bias (positive serial dependence), pulling current judgments toward the preceding proportion. Furthermore, the magnitude and direction of this serial dependence appeared to be modulated by both the participants confidence in their judgments and the feature similarity between successive stimuli. These findings suggest that the perception of proportion has serial dependence and extend the generality of this phenomenon to higher-level visual summary statistics.