Serial dependence generalizes across different stimulus formats, but not different sensory modalities.

Visual perception is thought to be supported by a stabilization mechanism integrating information over time, resulting in a systematic attractive bias in experimental contexts. Previous studies show that this effect, whereby a current stimulus appears more similar to the one previous to it, depends on attention, suggesting an active high-level mechanism that modulates perception. Here, we test the hypothesis that such a mechanism generalizes across different stimulus formats or sensory modalities, effectively abstracting from the low-level properties of the stimuli. Participants performed a numerosity discrimination task, with task-relevant dot-array stimuli preceded by a sequence of visual (flashes) or auditory (tones) stimuli encompassing different numerosities. Our results show a clear attractive bias induced by visual sequential numerosity affecting an array of simultaneously presented dots, thus operating across different stimulus formats. Conversely, auditory sequences did not affect the judgment on visual numerosities. Overall, our results demonstrate that serial dependence in numerosity perception operates according to the abstract representation of numerical magnitude of visual stimuli irrespective of their format. These results thus support the idea that a high-level mechanism mediates visual stability and continuity, which integrates relevant information over time irrespective of the low-level sensory properties of the stimuli.