Sensory Feedback Coding Strategy Based On Evoked Tactile Sensation

Prosthetic hands are the main compensatory tools to help upper limb amputees recover motor functions.However,the lack of sensory feedback influences the use of prosthetic hands.Apply transcutaneous electrical stimulation on the projected-finger maps(PFM)of evoked tactile sensation(ETS)could reconstruct sensory feedback pathway.How to transmit the external multi-modality sensory information contacted by prosthetic hands to amputees needs to be addressed urgently.This article firstly explored the neural mechanism of evoked tactile sensation by establishing an objective analysis method to evaluate the response activity of the cerebral cortex when the PFM are induced by electrical stimulation.The results showed that the response area distribution of the PFM was consistent with that of the contralateral finger,which confirmed that there was a direct neural pathway between the PFM of ETS and the cerebral cortex.In addition,this article establishes a set of experimental protocol to evaluate the coding strategies of different electrical stimulation-induced finger sensations,which are mainly divided into the following three parts:(1)Coding space evaluation of sensations induced by electrical stimulation.By adjusting the parameters of the stimulus pulse output by the stimulator,the coding interval of the electrical stimulus parameters of different sensations was explored.Results showed that subjects could feel touch,buzz,vibration,numb and tingling sensation;Among them,buzz sensation and vibration sensation have the widest pulse width coding interval at 20 Hz and 50 Hz,respectively.(2)Sensitivity assessment of sensations induced by electrical stimulation.The sensitivity of sensations was evaluated by measuring the minimum pulse width changes distinguishable.The results showed that the minimum pulse width of vibration and buzz sensation was about 20μs,suggesting that the subjects were able to distinguish the sensory intensity.(3)Coding and verification of sensations induced by electrical stimulation.Based on the pressure sensory feedback system,finger identification experiment was carried out to verify the feasibility of sensations coding.The pulse width interval corresponding to the buzz sensation is used to linearly encode the external pressure value.The accuracy of single finger recognition in both subjects was more than 70%.This study suggests that it is feasible to encode external information by the sensations induced by electrical stimulation in the projected-finger maps of evoked tactile sensation.This study proved that in the evoked tactile sensory feedback,the stimulus encoding strategy of sensations is effective,and the encoding strategy can provide the finger-to-finger sensory information for amputees.For each upper limb amputee who needs to wear a prosthetic hand,this protocol can be used to customize the electrical stimulation coding interval of different sensations,thus improving the amputee’s ability to perceive the external multi-modality information with finger to finger.