Abstract
In the mirror visual-feedback paradigm, the mirrored hand image directly affects the sense of motion of the hand hidden behind the mirror (mirror kinesthetic illusion). Our previous study found that the kinesthetic illusion was observed even when both hands were not anatomically congruent, suggesting that showing the hand image in the mirror is not a minimal requirement for inducing the kinesthetic illusion. However, what critical factor yields this illusion in such an incongruent situation remains unclear. This paper introduces a new concept of “hand imaginability” relating to what extent we can imagine an “invisible hand” in the mirror when the mirror does not in fact reflect the hand. This experiment asked participants to report the hidden hand’s subjective speed using the original mirror visual-feedback setup and examined the effect of the handle’s visuo-tactile congruency. The result showed that the kinesthetic illusion became active mainly when the same shaped handle was used on both sides, suggesting a significant contribution by the invisible hand’s imaginability.
