A surprise induced by a visual-haptic illusion in virtual reality can lead to motor improvement

This study assessed the preliminary results of an experimental protocol evaluating the impact of positive expectations on fingertip-to-floor distance during forward bending. Thirty-six participants were assigned to three groups, each receiving a sham physical manipulation in Immersive Virtual Reality (IVR). The first group received a neutral statement about the manipulation's efficacy, while the second and third groups were told the manipulation would improve forward bending, emphasising its fictious positive effect to increase expectations for a beneficial motor improvement. Additionally, the third group also experienced a visual-haptic illusion, by lifting a tile in front of participants and raising the floor in the virtual scenario, creating the belief of reaching the floor thanks to the received manipulation. Fingertip-to-floor distance was measured at baseline, immediately after the manipulation (after-effect), and five minutes later (follow-up). Differences between baseline and after-effect/follow-up distances represented the gained distances. Only the third group, which experienced the combined effect of positive verbal statement reinforced by the visual-haptic illusion, showed a significant increase in gained distance during the after-effect and follow-up phases compared to the neutral statement group. These findings support the potential of this multifactorial intervention to promote motor improvement by enhancing positive expectations.