Illusory Motion Reversal in Touch

Abstract

Psychophysical visual experiments have shown illusory motion reversal (IMR), in which the perceived direction of motion is the opposite of its actual direction. The tactile form of this illusion has also been reported. However, it remains unclear which stimulus characteristics affect the magnitude of IMR. We closely examined the effect of stimulus characteristics on IMR by presenting moving sinusoid gratings and random-dot patterns to 10 participants’ fingerpads at different spatial periods, speeds, and indentation depths. All participants perceived a motion direction opposite to the veridical direction some of the time. The illusion was more prevalent at spatial periods of 1 and 2 mm and at extreme speeds of 20 and 320 mm/s. We observed stronger IMR for gratings and much weaker IMR for a random-dot pattern, indicating that edge orientation might be a major contributor to this illusion. These results show that the optimal parameters for IMR are consistent with the characteristics of motion-selective neurons in the somatosensory cortex, as most of these neurons are also orientation-selective. We speculate that these neurons could be the neural substrate that accounts for tactile IMR.

Voluntary modification of rapid tactile-motor responses during reaching differs from its visuomotor counterpart

“…The study of tactile sensation is heavily influenced by our knowledge of the vision. The tactile and visual systems are capable of extracting similar stimulus features (Pack & Bensmaia 2015), and parallels between visual and tactile processing yield interesting results (Pei et al 2008, Pruszynski et al 2018, Hsu et al 2019. Our results caution against general inferences about the properties of the tactile motor system based on the visual motor system.…”

A Novel Tactile Function Assessment Using a Miniature Tactile Stimulator

“…MTS is a robotic tactile stimulator that could be applied for tactile function capability assessments [ 17 , 18 , 23 ]; it is novel because a standard and feasible method has yet to be established. In the present study, we developed an MTS-based program for tactile acuity evaluation.…”

“…MTS consists of three independently controlled micromotors, providing three degrees of freedom, which are the grating ball’s direction of movement, speed of rotation, and depth of vertical indentation on the skin [ 17 ]. We successfully demonstrated the functionality of the MTS for measuring the performance of tactile motion discrimination in healthy participants [ 17 , 18 , 19 ], and the MTS thus offers unique potential as a fully automatic and standardized measurement of tactile acuity.…”