Toward an artificial sensory feedback system for prosthetic mobility rehabilitation: Examination of sensorimotor responses

Abstract

Abstract-People with lower-limb amputation have reduced mobility due to loss of sensory information, which may be restored by artificial sensory feedback systems built into prostheses. For an effective system, it is important to understand how humans sense, interpret, and respond to the feedback that would be provided. The goal of this study was to examine sensorimotor responses to mobility-relevant stimuli. Three experiments were performed to examine the effects of location of stimuli, frequency of stimuli, and means for providing the response. Stimuli, given as vibrations, were applied to the thigh region, and responses involved leg movements. Sensorimotor reaction time (RT) was measured as the duration between application of the stimulus and initiation of the response. Accuracy of response was also measured. Overall average RTs for one response option were 0.808 +/-0.142 s, and response accuracies were >90%. Higher frequencies (220 vs 140 Hz) of vibration stimulus provided in anterior regions of the thigh produced the fastest RTs. When participants were presented with more than one stimulus and response option, RTs increased. Findings suggest that long sensorimotor responses may be a limiting factor in the development of an artificial feedback system for mobility rehabilitation applications; however, feed-forward techniques could potentially help to address these limitations.

Effects of cognitive load and prosthetic liner on volitional response times to vibrotactile feedback

“…Interactions between the test condition and frequency, as well as the test condition and stimulus location were also examined to further isolate the effects of frequency and location, respectively within condition. The results of Experiment 1 agree with previous research [12] showing that RTs from the 180 Hz stimulation consistently fall between RTs from the 140 Hz and 220 Hz frequencies. Therefore, Experiment 2 included only these latter two frequencies for statistical analysis.…”

“…Building on previous work, which investigated variables relating to the stimulator type and location [12], the focus of this work was to specifically examine the effects of a cognitive load and the presence of a liner on volitional responses to feedback stimuli. Overall, the findings suggest that both conditions do have an effect on increasing RTs.…”

“…The motors (Model 310-101, Precision Microdrives, Inc; London, United Kingdom) employ a rotating offset mass that when attached to the body produce shear forces in plane with the skin surface and proportional to the speed (frequency) of the motor. Each motor was calibrated to operate at the vibratory frequencies required for the study: 140, 180, and 220 Hz [12]. The Arduino Mega 2560 processor from Sparkfun Inc (Niwot, Colorado) was used with an N-type MOSFET (metal-oxide-semiconductor field-effect transistor) to control the vibrotactile motors.…”

“…Testing was performed on the dominant and amputated legs of the nondisabled and amputee participants, respectively. It should be noted that data presented in this study were collected as a part of another study described in a previous article exploring the effects of vibration frequency and location on RTs and were collected using similar experimental protocols [12]. The following experiments were performed.…”

“…The studies have identified important design requirements for such systems and even demonstrated their potential to improve certain aspects of balance in individuals with LLA [4,[9][10]. Specifically, these studies have explored the efficacy of different mechanisms for delivering artificial sensory information, assessing the influence of factors such as stimulus location and stimulus type on both the sensitivity to stimulus and time to voluntary muscle response [11][12]. The time delay between stimulus detection at the mechanoreceptors and voluntary muscle action is especially important for mobility applications, such as gait, where reactions to external stimuli must fall within a small time window to ensure continuous fluid motion.…”