Tactile-Based Pantomime Grasping: Knowledge of Results is Not Enough to Support an Absolute Calibration.

Tactile-based pantomime-grasping requires that a performer use their right hand to 'grasp' a target previously held in the palm of their opposite hand - a task examining how mechanoreceptive (i.e., tactile) feedback informs the motor system about an object property (i.e., size). Here, we contrasted pantomime-grasps performed with (H+) and without (H-) haptic feedback (i.e., thumb and forefinger position information derived from the grasping hand touching the object) with a condition providing visual KR (VKR) related to absolute target object size. Just-noticeable-difference (JND) scores were computed to determine whether responses adhered to - or violated - Weber's law. JNDs for H+ trials violated the law, whereas H- and VKR trials adhered to the law. Accordingly, results demonstrate that haptic feedback - and not KR - supports an absolute tactile-haptic calibration.