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.