Bias in Visual Short-Term Memory for Motion Induced by Perceptually Suppressed Distractors

Interference between visual short-term memory (VSTM) and task-irrelevant sensory distractors is a well-documented phenomenon across a wide range of visual features. Although this sensory-memory interference is believed to result from neural interactions between mnemonic and sensory processing, the nature of the interfering signals remains unclear, particularly whether the interference originates from physical stimuli entering the retina or the resulting subjective perception. Here we addressed this question by leveraging perceptual invariance during smooth pursuit eye movements, where retinal motion induced by eye movements is perceptually suppressed. Distractors were presented as either physical object motion in world coordinates or apparent motion of a stationary background induced by eye movements, allowing us to generate identical retinal motion with distinct perception. Human observers (both female and male) were tasked with comparing the speeds of two sequentially presented motion stimuli while ignoring the distractor stimuli presented between them. Our results showed that the retinal motion distractor systematically biased the memorized motion speed. Crucially, the magnitude of the bias was comparable regardless of whether the retinal motion distractor reflected physical or apparent motion. Notably, the distraction effect of the eye movement-induced retinal motion was successfully replicated using a classifier trained on data from the physical motion condition. A further experiment confirmed that this distraction effect by the apparent motion was not due to eye movements themselves. These findings provide behavioral evidence that, at least for the feature of motion speed, perception is not required for the emergence of a bias in VSTM.