The size-distance scaling of real objects and afterimages is equivalent in typical but not reduced visual environments.

Size constancy refers to the human ability to perceive an object as having the same size, despite changes in its retinal image caused by variations in viewing distance. The relationship between perceived size and perceived distance is predicted by Emmert's law. This study investigated whether the principles of size constancy apply in the same way to afterimages and real objects, hypothesising that perceptual equivalency would result in consistent size-distance scaling constancy for both types of stimuli. Twenty participants completed a size judgment task involving real objects and afterimages presented under binocular, monocular, and complete darkness conditions. Results showed that both types of stimuli adhered to Emmert's law under binocular conditions; however, afterimages exhibited greater deviations in monocular and dark environments, indicating a breakdown in size constancy. While real objects maintained perceptual scaling even in reduced environments, afterimages displayed diminished accuracy in size and distance perception, especially in darkness. The findings support the signal ambiguity theory, suggesting that afterimages rely more heavily on contextual information due to the lack of stable external references. This study highlights the utility of afterimages as a tool for exploring the limits of visual perception, offering insights into how the visual system handles ambiguous signals.