The effects of prediction errors and movement speed on pseudo-haptic sensations.

Pseudo-haptic sensations are illusory haptic experiences induced by manipulating the visual feedback of object movements. Previous studies have suggested that such sensations arise from prediction errors generated by a forward model, defined as the discrepancy between predicted and actual outcomes. In contrast, other studies propose that pseudo-haptic sensations emerge from a simple statistical relationship between weight and movement speed (e.g., heavier objects move more slowly), with prediction errors being only a by-product. In the present study, we further investigated the mechanisms underlying pseudo-haptic sensations by separating spatial prediction errors from movement speed. Participants moved a cursor along a sine-wave-shaped pathway using a mouse. The cursor's movement direction was generated by combining participants' real-time mouse movements with pre-recorded movements from another individual, producing three levels of control. The cursor's movement speed remained proportional to the mouse movement. On the other hand, when the cursor entered a central painted zone on the screen, its speed was reduced by three different ratios while remaining proportional to the mouse movement. Participants rated their sense of resistance in the hand and their sense of agency over the cursor's movement. A linear mixed-effects model analysis, with spatial prediction error and the time required to reach the end of the pathway as fixed effects and participant as a random effect, showed that both spatial prediction error and effective movement speed (indexed by trial completion time) significantly contributed to the sense of resistance. Taken together, these findings suggest that both prediction errors and object movement speed contribute to pseudo-haptic sensations, likely through different processes.