The implied motion aftereffect changes decisions, but not confidence

Abstract

Viewing static images depicting movement can result in a motion aftereffect: people tend to categorise direction signals as moving in the opposite direction to the implied motion of still photographs. This finding could indicate that inferred motion direction can penetrate sensory processing and impact perception. Equally possible, however, is that inferred motion impacts decision processes, but not perception. Here we test these two possibilities. Since both categorical decisions and subjective confidence are informed by sensory information, confidence can be informative about whether an aftereffect likely results from changes to perceptual or decision processes. We therefore leveraged subjective confidence as an additional measure of the implied motion aftereffect. In Experiment 1 (implied motion), we find support for decision-level changes only, with no change in subjective confidence. In Experiment 2 (real motion), we find equal changes to decisions and confidence. Our results suggest the implied motion aftereffect produces a bias in decision-making, but leaves perceptual processing unchanged.