Serial Dependence Under Transparent Distraction: Encoding vs. Decoding Influences

Abstract

The perceptual system must reliably interpret incomplete sensory input that inherently contains both internal and external noise. To achieve stable perception, the system exploits the temporal statistics of visual stimuli, which are correlated over time. As a result, the perceptual system incorporates information from previous stimuli and previous responses when processing current inputs, producing biases in current perception, a phenomenon known as serial dependence. Serial dependence has been reported across multiple visual features, including orientation, motion, and face identity. However, prior studies have primarily focused on serial dependence for attended stimuli and have not examined how the presence of distractors alters this effect. In natural environments, targets often appear alongside transparent distractors that must be suppressed, and these distractors may modulate serial dependence. The present study investigates how distractor stimuli presented in the current and previous trials influence the processing of sequential sensory information. Participants performed a direction judgment task in which two different colored moving dots were presented transparently. The results show that serial dependence driven by previous responses does not directly influence the perceived direction of the current target; instead, it acts on the distractor-biased direction that has been shifted by the current distractor. This indicates that the influence of previous responses arises during the decoding stage, after the target signals have been encoded. Additionally, the effects of previous target and distractor stimuli were determined by their motion directions rather than the color feature that distinguished the two stimuli. Importantly, the influence of the previous distractor exhibited a different pattern from that of the previous target, suggesting that distractors alter the encoding stage by contributing direction specific information that differs from the target driven bias. Overall, this study demonstrates that the presence of distractors modulates the processing of sequential sensory input. Furthermore, it provides empirical evidence that previous response effects emerge during the decoding stage, whereas previous stimulus effects originate during the encoding stage. The significance of this work lies in showing how the perceptual system integrates not only target information but also transparent distractor signals when forming perceptual estimates over time.