Exploring Synergy Between Tactile Perception and Arm Usage.

Stroke causes severe tactile deficiencies which affects motor control when grasping and lifting objects. Understanding the fundamental neural disorders associated with tactile deficits is crucial to developing rehabilitation and treatment plans correspondingly. Earlier studies have studied the dynamics between finger grasping behavior and arm muscle activation in stroke patients. However, the exact neuromuscular synergy of tactile perception and arm usage is left unexplored. Here we designed a comprehensive experiment platform and tested the potential synergy on 12 healthy young adults, serving as a control group to establish a foundation for future studies on stroke patients. The experimental platform consists of a lever arm on which torques can be applied to the subject's arm. The end effector is equipped with a special ultrasonic friction modulation plate that can reduce the apparent friction of the object by up to 63 %, simulating real-world grasping tasks in a controlled setting. The experiments were performed under varying conditions of friction and arm usage. Results indicate significant effects of tactile stimulation on grasping force adaptation ($p<0.05$ in 8 of 12 experimental conditions). In the meantime, arm usage did not show a significant synergy with tactile perception ($p=0.44$ in grasping force adaptation amplitude, and $p=0.73$ in reflex delay). These findings demonstrate that the experimental platform can provide insights into human tactile behaviors, which is critical for studying tactile sensory and motor control synergy. The results will lay the groundwork for future research on underlying pathologies and rehabilitation strategies for stroke patients.