Dynamic tracking delays using high resolution electro-tactile feedback

The development of a high resolution electrotactile feedback display with spatial coding, designed to explore the limits of electrotactile feedback for use in prosthetic control systems, is discussed. Specifically, the delays between input and output for the dynamic tracking of randomly appearing targets is measured for the natural arm and for a rate-command-driven (computer modeled) prosthetic arm with visual or tactile feedback. The outputs lag the targets by 0.2-0.3 s, 0.3-0.4 s, and 0.4-0.6 s, respectively. Reducing the feedback resolution does not increase these delays. The electrotactile feedback channel results also show evidence of considerable low-frequency drift of the operator´s zero reference point, and this shows up as low-frequency noise in the output. Some simple hardware modifications to reduce this noise is suggested