Real objects maintain superior size-distance scaling to afterimages under sudden and adapted darkness conditions

Human vision must adapt to varying lighting conditions, particularly in low-light environments where depth perception and size constancy are challenged. This study examined size-distance scaling for real objects and afterimages under sudden and adapted darkness conditions. Real objects exhibited more stable scaling than afterimages, closely aligning with Emmert’s law, while afterimages showed substantial deviations. Although dark adaptation modestly improved size-distance scaling for both stimulus types, it did not fully restore veridical perception. Contrary to expectations, afterimages did not benefit more from adaptation than real objects, suggesting that their reliance on external depth cues exceeds what mesopic adaptation alone can compensate for. Additionally, perceived brightness influenced distance misperceptions, with brighter stimuli associated with greater errors—particularly for real objects. These findings highlight the limitations of internally generated stimuli in maintaining perceptual stability in darkness and emphasise the critical role of environmental and stimulus-based depth cues in supporting size constancy.