Evoked Tactile Feedback for Fingertip Force Using Transcutaneous Electrical Nerve Stimulation with Concurrent Frequency and Pulse Width Modulations

Fingertips are the most active portions of our fingers during interaction with our surroundings. The incorporation of tactile feedback to the fingertips may enhance perception and interaction with the real environment. Frequency., pulse width., and amplitude modulations of transcutaneous electrical nerve stimulation (TENS) are extensively studied to elicit sensory feedback in hand for sensorimotor function. However., in this study., a new approach to eliciting tactile feedback was investigated using TENS frequency., pulse width., and their novel concurrent modulations in linearly positive and negative correlations for fingertip forces. An instructor regulated the TENS parameters by fingertip force to invoke tactile sensation, and participants administered response fingertip force to a force sensor resistor to express the nature (strength) of the evoked tactile sensation. The ratio of response fingertip force to stimulation fingertip force, abbreviated as the fingertip force elicitation ratio (ER), was examined for each TENS modulation in terms of mean and maximal fingertip forces. The results exhibited that both conventional (frequency and pulse width) and novel concurrent modulations of frequency and pulse width TENS can evoke tactile feedback for fingertip force control. Furthermore, the results demonstrated that the fingertip forces resulting from tactile feedback induced by concurrent frequency and pulse width modulations were stronger., more stable, and more consistent compared to the forces produced by their independent modulations. Future applications of the innovative concurrent TENS modulations may include evoking tactile feedback responses for grasping tasks, touchpad gestures, fingertip force control, and intelligent prostheses.