Multiple trajectories of proprioceptive drift in the mirror box illusion

The mirror box illusion creates a visual-proprioceptive conflict in which an observer's hidden hand feels like it occupies the position of their other hand's viewed reflection. We used this illusion to explore the temporal dynamics of multisensory conflict resolution, recording perceived hand position repeatedly while manipulating visual-proprioceptive congruence across four experiments within a neurotypical population (N = 181). Conditions with greater visual-proprioceptive congruence strengthened the illusion. Surprisingly, however, we found that the illusion follows multiple trajectories: abrupt shifts, gradual drifts, immediate onset, or no illusion at all. These trajectories are unevenly distributed across individuals, suggesting differences in observers' experience of this illusion. We advance a possible explanation in which these different trajectories could be produced by three algorithmically distinct causal inference mechanisms. By tracing the perceptual time course of individual trials, we find heterogeneity which may offer insights into the mechanisms underlying this multisensory illusion.