Combining visual and haptic practice significantly reduced deviations in haptic parallelity matching

This is most likely due to the biasing influence of the egocentric reference frame. Even presenting participants with either haptic or visual information about parallelity or direct error feedback did not result in veridical performance.

The present study was set up to assess to what extent haptic performance could be improved by providing combined visual and haptic practice. Thirty-two participants (sixteen females and males) used their dominant hand to make a test bar parallel to a reference bar located at the side of the nondominant hand. Haptic sessions (in which participants were blindfolded and had to perceive parallelity using their hands) were alternated with visual sessions (in which they could physically see both bars and could also use their eyes to perceive parallelity on the test bar without feeling the reference bar) over a series of eleven sessions.