Force illusion induced by visual illusion: Illusory curve in cursor path is interpreted as unintended force

Discrepancies between expected and actual visual outcomes of motor action can produce an illusory sensation of unintended force. In the present study, we addressed whether the force illusion could be induced even when the discrepancy was brought about by the illusory appearance of the actual outcome. Specifically, the apparent path of a cursor controlled by the participants was modulated by the direction of noise motion presented inside the cursor. We showed that a greater noise motion inside the cursor caused a greater apparent curve of the cursor path and, also, higher rating scores for an unintended force. We also found that the unintended force was influenced strongly by the visibility of the cursor, suggesting that the apparent curve of the cursor path was a more important factor in generating the unintended force than the noise motion itself inside the cursor. Our results suggest that the illusory force, which is mediated by cross-modal mechanisms susceptible to visual illusion, can be exploited in extended reality systems as a novel technique for giving users a sensation of force.