Browsing by Author "Farrell, Todd R."

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    PHANTOM LIMB SENSORY FEEDBACK THROUGH NERVE TRANSFER SURGERY
    (2005) Sensinger, Jonathon W.; Kuiken, Todd; Farrell, Todd R.; Weir, Richard F.
    Commercially used prostheses are essentially open-loop devices and provide little or no feedback to the amputee as to how much force they exerting with the terminal device, despite numerous attempts to provide closed loop control in prosthetics [1]. Providing pressure feedback clearly has great value for function of the prosthesis—the goal is for the amputee to ‘feel’ what they are holding. Indirect pressure feedback has been attempted by methods including vibration [2] and functional electrical stimulation [3, 4]. The information contained in these forms of feedback is not in the same modality as that which they sense. As a result, while providing information to the user, it is likely that it comes at the cost of increased mental load and low level of information transfer [5]. Patterson and Katz [6] have obtained better qualitative feedback with pressure to pressure feedback than with pressure to vibratory or electrical stimulation feedback, offering support for this suggestion. An adaptive process is still involved since the subject must learn to associate pressure in one area with pressure in another area. Ideally, the sensory nerve endings of the amputated area need to be stimulated in direct correlation to the function of the prosthesis. The recent work of Kuiken [7] has made this concept feasible by the use of targeted reinnervation. The potential thus exists for the subject to feel as if touch, pressure and even hot or cold temperatures are being exerted on their hand. This study will examine the potential of intuitive pressure feedback.
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    SURFACE VS. IMPLANTED EMG FOR MULTIFUNCTIONAL PROSTHESIS CONTROL: PILOT RESULTS
    (2005) Farrell, Todd R.; Weir, Richard F.
    It has been hypothesized that, due to the potential to both provide a larger number of independent control sites and selectively record from forearm muscles (in particular the deep muscles), intramuscular EMG should be advantageous for multifunctional prosthesis control [1]. The use of surface electromyograms (EMG) to control a multiple degree-of-freedom prosthesis has been investigated for several decades. A variety of approaches have been employed with groups using different numbers of input channels [2-3], feature extraction methods [3-6] and pattern recognition algorithms [3,7-8]. While much work has been done, all of these efforts have used surface EMG as the control signal. Only a single preliminary study was found that acquired intramuscular EMG for prosthesis control [9]. Admittedly, the technology has not existed for chronic intramuscular recordings to be clinically feasible for prosthetic use. The Implantable Myoelectric Sensor (IMES) that is being developed at the Northwestern University Prosthetic Research Laboratory will make chronic intramuscular recordings clinically feasible [10]. We hypothesize and hope to demonstrate that by utilizing intramuscular EMG it will be possible to substantially increase classification accuracies of multifunctional prosthesis controllers (i.e., increase the percentage of the time that the controller can correctly predict the intended movement of the user). If a substantial increase in classification accuracy is demonstrated, this will justify the invasiveness of using these devices. However, if similar accuracies can be obtained from surface recordings then there will be little justification for pursuing these devices for transradial prosthesis control purposes.
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    THE EFFECT OF CONTROLLER DELAY ON BOX AND BLOCK TEST PERFORMANCE
    (2005) Farrell, Todd R.; Weir, Richard F.; Heckathorne, Craig W.
    Multifunctional prosthesis controllers have shown higher classification accuracies when EMG feature extraction and pattern recognition are performed on time windows of longer duration [1] (see figure 1). However, there is a limit to the time over which EMG data can be collected and analyzed before the delay causes the control of the prosthesis to become cumbersome. While no one has objectively examined the impact of controller delays on performance, the controller delay that can be present before prosthesis control degrades has been debated. Childress and Weir [2] believe that controller delays should be kept below 50 ms to ensure that these delays are imperceptible to the user. However, another group has stated that delays as large as 300 ms are not perceivable by the user [3-4] and, while they have not commented on the effect of these delays on performance, they have stated that a 300 ms delay is acceptable for control of a prosthesis. The desired controller delay may affect the choice of signal processing and pattern recognition algorithms that can be utilized. Thus it would be beneficial to establish this value for future investigations. Experiments were designed to find the longest period of delay that does not significantly degrade prosthesis performance and can thus be dedicated to EMG collection and processing.