The Impact of Stimulation Intensity on Spatial Discrimination with Multi-Pad Finger Electrode

Abstract

Multi-pad electrotactile stimulation can be used to provide tactile feedback in different applications. The electrotactile interface needs to be calibrated before each use, which entails adjusting the intensity to obtain clear sensations while allowing the subjects to differentiate between active pads. The present study investigated how the stimulation intensity affects the localization of sensations using a multi-pad electrode placed on a fingertip and proximal phalange. First, the sensation, localization, smearing and discomfort thresholds were determined in 11 subjects. Then, the same subjects performed a spatial discrimination test across a range of stimulation intensities. The results have shown that all thresholds were significantly different, while there was no difference in the threshold values between the pads and phalanges. Despite the subjective feeling of spreading of sensations, the success rates in spatial discrimination were not significantly different across the tested stimulation intensities. However, the performance was better for distal compared to proximal phalange. Presented results indicate that spatial discrimination is robust to changes in the stimulation intensity. Considering the lack of significant difference in the thresholds between the pads, these results imply that more coarse adjustment of stimulation amplitude (faster calibration) might be enough for practical applications of a multi-pad electrotactile interface.

Design of multi‐pad electrotactile system envisioned as a feedback channel for supernumerary robotic limbs

“…The estimated probability density functions representing LT and DT as the percentage of ST showed a notable overlap (314% ST) between CIs for two thresholds. The same analysis was performed by Malešević et al 31 using multi‐pad electrodes placed on fingertips. They showed that 95% CI ranged from 123% ST to 176% ST for LT and from 185% ST to 526% ST for DT.…”

“…ST and DT are standard psychometric LT is a subjective measure introduced in Ref. [31] and defined as the current intensity producing clear sensations localized under the active pad.…”

“…Nevertheless, this procedure can be simplified by adapting the initial amplitude values in the calibration algorithm 30 . A recent study showed that the stimulation intensity does not affect the spatial discrimination in fingertips, suggesting that practical applications of multi‐pad interfaces could rely on short and simple calibration 31 …”

“…30 A recent study showed that the stimulation intensity does not affect the spatial discrimination in fingertips, suggesting that practical applications of multi-pad interfaces could rely on short and simple calibration. 31 This article presents the design of an electrotactile system for SRLs. In line with previously noted advantages and drawbacks of the electrotactile approach, the system considers a design of the custom electrode for providing feedback from SRL to the lower limb and the definition of the procedure for calibration of the proposed electrode.…”

Electrotactile Communication via Matrix Electrode Placed on the Torso Using Fast Calibration, and Static vs. Dynamic Encoding

“…Recent technological advances such as flexible memory devices [ 27 ], Bipolar Junction Transistor-based biosensors [ 28 ] and graphene-based humidity sensors [ 29 ] are promising in terms of further device miniaturization and garment integration, as well as the potential design of integrated closed loop systems. However, as explained before, the calibration is a drawback of this technology, and a significant effort was dedicated to simplifying the electrotactile calibration procedures [ 30 , 31 ].…”