Examining the time course of visuoproprioceptive integration using the mirror box illusion
Grant T. Fairchild, Yuqi Liu, Riwa Safa, Jared Medina · Journal of Vision · 2025
The mirror box illusion creates a visuoproprioceptive conflict between the actual position of the hand behind the mirror and the reflection of the participant’s viewed hand. After synchronous movement or even passive viewing of the hand over time, participants will report feeling their hand where they see it. Although the illusion involves evidence accumulation over time, the relationship between evidence accumulation and perceptual qualia is poorly understood. One possible mechanism is an abrupt state transition in which the visual estimate of hand position overrides the proprioceptive estimate as soon as the accumulated evidence favoring vision surpasses a certain threshold. Alternatively, the illusion may reflect a gradual shift in weighting given to the visual vs. proprioceptive estimates as evidence favoring vision accumulates. To investigate the temporal progression of the mirror box illusion, we recorded observers’ perceived hand position every five seconds in a series of experiments manipulating several factors that modulate the congruence between visual, motor, and proprioceptive signals. As expected, we find that the illusion is strengthened by factors increasing the congruence between the hidden and reflection hand, including synchronous movements, decreased scalar or angular distance, and reduced biomechanical constraints. Notably, we find that the illusion can proceed along both abrupt and gradual trajectories: Sometimes, participants perceive an abrupt transition in the perceived position of their hand, as though their hand suddenly snapped into the position of the reflection, while other times, participants perceive a gradual shift in hand position, as though their hand slowly drifted towards the position of the reflection. Furthermore, there appear to be consistent individual differences in observers’ tendency to experience the illusion abruptly or gradually. We discuss the implications of these findings for the mechanisms of resolution of visual-proprioceptive conflict.