Skin displacement and velocity contribute to perception of force direction: insights from illusory tactile pulling sensations

Humans perceive tangential force at the fingertip through skin deformation characterized by kinematic components, such as displacement, velocity and acceleration. However, their respective contributions to the perception remain unclear because these components typically covary in natural stimuli, making experimental dissociation difficult. Precise understanding of these contributions is essential, not only for elucidating how the human brain interprets mechanical interactions between the body and the environment, but also for designing haptic feedback that is now widely used in modern digital devices. To address the issue, we focused on an illusory pulling sensation induced by asymmetric vibration. The stimuli were systematically varied to maximize asymmetries in the different components under distinct conditions, and participants reported the perceived force direction in a two-alternative forced-choice paradigm, designed to directly compare their relative contributions to our force perception. Our results show that perceived direction is primarily accounted for by directional cues in displacement and velocity. The model analysis further revealed that displacement provides the largest contribution among the considered kinematic components. These findings refine the prevailing emphasis on dynamic phases of the stimulus by showing that displacement plays a major role, alongside velocity, in shaping perceived force direction.