The time course of multisensory integration in the body using the mirror-box illusion
Date
2022
Authors
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Publisher
University of Delaware
Abstract
In the mirror-box illusion, a paradigm used to investigate multisensory integration in the body, individuals tend to perceive their hand to be closer to the hand they see in the mirror (visual) compared to the hand placed behind the mirror (proprioceptive) when the two hands are spatially displaced. Studies using the rubber-hand illusion have found that the proprioceptive shift increased gradually over time (2 minutes) to resolve the discrepancy between the proprioceptive (hidden) and visual (rubber) hands through an accumulation of evidence. In our experiments, we used the mirror box illusion to examine the time course of multisensory integration in the body. However, during initial testing, we found that the illusion can happen in two qualitatively different ways: either abruptly or gradually as shown in the rubber hand illusion. We then aimed to explore the types of shifts observed, how they unfold over time, and whether they could result in different final estimates. Subjects placed their hands on each side of the mirror with the visual and proprioceptive hands spatially displaced and tapped their index finger either synchronously or asynchronously. In Experiment 1, they were instructed to report their perceived hand location every 5 seconds (frequent measurement) or at the end of the trial (infrequent measurement). We did not find an association between the types of shifts and the frequency of measurement or temporal congruency and there was no difference in the abruptness of gradualness of the shifts between the conditions. Moreover, frequency of measurement did not break down the illusion. However, temporal congruency affected the final estimate of the illusion and how it unfolds over time. In Experiment 2, we aimed to control for potential observer’s and expectancy effects due to the prompts and instructed the subjects to report any changes in perception (self-report). These results were consistent with the ones from Experiment 1. Moreover, the types of response appeared to influence how the illusion unfolds over time which could suggest that the system may be more liberal in one condition (self-report) and more conservative in another (frequent measurement) in perceiving changes. In Experiment 3, we increased the spatial disparity between the visual and proprioceptive hands to examine its effects on our dependent variables. We found further evidence that the general rules of multisensory integration do not appear to influence the type of shift observed. We thus proposed that top-down processes occurring before the beginning of the trial, primarily the prior for a common cause, could potentially explain the two types of shifts observed. ☐ Keywords: mirror-box, illusion, time course, causal inference, proprioceptive shift, multisensory integration, Kalman filters
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Keywords
Causal inference, Mirror-box illusion, Multisensory integration, Optimal weighting principle, Proprioceptive shift, Time course