Date Published: January 16, 2019
Publisher: Public Library of Science
Author(s): Andres E. Pena, Liliana Rincon-Gonzalez, James J. Abbas, Ranu Jung, Yih-Kuen Jan.
Current myoelectric prosthetic limbs are limited in their ability to provide direct sensory feedback to users, which increases attentional demands and reliance on visual cues. Vibrotactile sensory substitution (VSS), which can be used to provide sensory feedback in a non-invasive manner has demonstrated some improvement in myoelectric hand control. In this work, we developed and tested two VSS configurations: one with a single burst-rate modulated actuator and another with a spatially distributed array of five coin tactors. We performed a direct comparative assessment of these two VSS configurations with able-bodied subjects to investigate sensory perception, myoelectric control of grasp force and hand aperture with a prosthesis, and the effects of interface compliance. Six subjects completed a sensory perception experiment under a stimulation only paradigm; sixteen subjects completed experiments to compare VSS performance on perception and graded myoelectric control during grasp force and hand aperture tasks; and ten subjects completed experiments to investigate the effect of mechanical compliance of the myoelectric hand on the ability to control grasp force. Results indicated that sensory perception of vibrotactile feedback was not different for the two VSS configurations in the absence of active myoelectric control, but it was better with feedback from the coin tactor array than with the single actuator during myoelectric control of grasp force. Graded myoelectric control of grasp force and hand aperture was better with feedback from the coin tactor array than with the single actuator, and myoelectric control of grasp force was improved with a compliant grasp interface. Further investigations with VSS should focus on the use of coin tactor arrays by subjects with amputation in real-world settings and on improving control of grasp force by increasing the mechanical compliance of the hand.
Current upper-limb prosthetic limbs are limited in their ability to provide direct sensory feedback to users, resulting in increased reliance on visual cues and attentional demands [1,2]. The use of visual feedback for estimating the degree of hand aperture can be unreliable under many conditions, including visual occlusion or limited lighting. Moreover, determining and controlling grasp force outputs from visual feedback alone can prove a more difficult task than aperture control in the absence of visibly noticeable object deformation. This can result in damage to the object being handled (i.e. crushing or dropping the object) even under optimal visual conditions [3,4]. Sensory feedback from prosthetic limbs could enable amputees to better control the prosthesis in a graded manner (i.e. gradually change grasp force and aperture), perform precise tasks while reducing attentional demands , and potentially promote prosthesis embodiment [6,7], thereby improving their quality of life.
In this study, we developed a vibrotactile sensory substitution (VSS) system using a single burst-rate modulated actuator (A1), and a spatially activated array of five coin tactors (T5). We performed a comparative assessment of these two VSS configurations with able-bodied subjects to investigate the VSS performance on perception and myoelectric control of grasp force and hand aperture tasks with a prosthesis. We also investigated the impact of interface compliance on the ability to perceive graded vibrotactile information, and control grasp force outputs with the myoelectric hand.
We investigated the performance of a single burst-rate modulated actuator and a spatially activated array of five coin tactors for providing feedback of grasp force and hand aperture feedback from a prosthesis. Performance on a perceptual task was not different for these two VSS configurations. However, during graded myoelectric control of grasp force and hand aperture, perception of feedback from the tactor array was better than perception from the single actuator. Graded control of grasp force with myoelectric control could be improved by increasing the compliance of the interface between the prosthesis and grasped object. Future studies should investigate the capability of VSS configurations to enhance the functionality of myoelectric prosthetic hands during daily activities in real-world environments.