Experimental study of the influence of friction and mass on finger pad mechanics during object lifting

On a daily basis, humans perform skillful manipulation tasks by properly adjusting their grip force to the diverse properties of an object. This continuous adaptation of the gripping behavior relies on the integration of an important amount of feedback by the central nervous system. Among these, tactile afferents, resulting from the complex mechanical deformations occurring at the fingertip-object surface, are encoded by mechanoreceptors, and are assumed to provide important information regarding surface properties. In addition, proprioceptive input presumably also contributes to accurate manipulation through muscle afferents. To better characterize how humans adjust to different friction and weight conditions, 15 participants were requested to perform a lift-off task with a device enabling to record both the applied forces as well as images of the fingertip deformations. The friction, as well as the weight of the device were changed throughout trials to gain insight on the mechanisms allowing adaptation of behavior to a new condition. The results show that adaptation to friction solely relies on tactile afferents, whereas adaptation to weight seemingly benefits from multisensory integration, wherein proprioceptive feedback would constitute the main source of information.