Visual serial dependence in an audiovisual stimulus

Serial dependence is a phenomenon that biases the perception of features or objects systematically toward sensory input from the recent past (Fischer & Whitney, 2014). There is an active debate whether this effect is rooted directly in perception or reflects biases in decision making. We investigated serial dependence across three experiments by manipulating the decision made on each trial. A multimodal audiovisual stimulus comprising a Gabor and a vowel sound was presented repeatedly. On each trial, participants reported either the Gabor orientation or the vowel sound. Participants either ignored one modality (Experiment 1) or attended to both modalities (Experiments 2 and 3). In Experiments 2 and 3, the response task was randomized to prevent anticipating which modality to respond to until the response phase. In Experiment 3, no-response trials were additionally interleaved. Results across the three experiments demonstrated serial dependence only when participants reported the visual modality. Serial dependence was also present in visual reports when participants completed auditory reports or made no reports on previous trials. The previous stimulus alone was enough to elicit an effect. Serial dependence is unlikely to be an effect of the previous decision on the stimulus, but rather an effect of perceiving the previous stimulus.