Synergistic Illusions: Enhancing Perceptual Effects of Pseudo-Attraction Force by Kinesthetic Illusory Hand Movement.

We investigated the enhancement of the perceived force strength in force feedback devices by combining the pulling illusion with kinesthetic illusions. The pulling illusion (i.e., a sensation of being pulled or pushed) is induced by asymmetric vibrations applied to the fingertips, enabling the implementation of small, lightweight, and ungrounded force feedback devices. However, the perceived force intensity is limited. We focused on the kinesthetic illusion, a phenomenon in which the movement of a limb in the direction of muscle extension is illusively perceived by presenting vibrations to tendons or muscles as an illusion that could enhance the perceived strength of the pulling illusion. Moreover, we investigated the perceptual characteristics of force sensation by combining a kinesthetic illusion induced by wrist tendon vibration stimulation with a pulling illusion. The findings demonstrate that the direction of the pulling illusion was accurately perceived, even with simultaneous wrist tendon vibration stimuli. Importantly, the results suggest that tendon vibration on the wrist, rather than cutaneous vibration on the wrist, enhances the perceived force intensity of the pulling illusion at the fingertips. These findings indicate the potential for expanding the expressive capability of the pulling illusion.