Tuning Feedback for Supernumerary Robotic Limbs Using Electrotactile Stimulation

Abstract

Sensory perception and the link of haptic feedback with operating and controlling supernumerary robotic limbs (SRLs) have been an area of interest. This project explored the perception of two adjacent points on the thigh by modulating the amplitude using electrotactile stimulation to enhance and provide the user with a more intuitive and embodied SRL system. It has been a critical challenge of SRLs control and development to create a robotic limb that is seamlessly embodied and integrated, giving the impression that they are an organic extension of the user's body. The employment of sensory electrotactile feedback will achieve the SRLs embodiment. Four participants were involved in this study, and the approach method was implementing a two-alternative forced-choice task. Each participant was subjected to electrotactile stimulation placed on their dominant thigh; the amplitude was modulated based on each participant's sensory perception. During the experiment, the participants were asked to identify the sensation of higher intensity based on two choices. The data was analyzed using a psychometric curve to illustrate the correlation between amplitude increments and the perceived intensity. The findings showed that amplitude modulation occasionally failed to produce the desired effect of creating similar feelings at the two nearby points. Rather, there appears to be a constraint in the modulation strategy because participants frequently felt that the two-pad stimulation was more intense than the reference pad. Regardless, an important observation was noted that when the range of threshold and discomfort levels within a single electrode pad was between 0.30 and 0.90 mA, there appeared to be a greater alignment in the participants' perception, favoring the reference pad. This might show there is a relationship between the parameters that should be explored in future studies. Therefore, these results highlight the difficulties in controlling sensory perception using electrotactile stimulation. They draw attention to the need for more studies into improving amplitude modulation techniques, emphasizing customized calibration according to unique sensory profiles. Research and development in this field are critical to creating more intuitive and user-friendly SRLs, which could greatly increase human capabilities and facilitate better human-robot interaction.