Optimization of single electrode tactile codes.

The effects of a frequency modulated electrocutaneous signal's (code's) characteristics on the interpretability of the signal were investigated using an electrocutaneous tracking approach. The characteristics investigated include the functional relationship (exponential and hybrid) between an informational signal and the stimulation frequency, the range of stimulation (2-50 Hz and 2-100 Hz), and the impact of pulse width compensation on a code's efficacy. The interpretability of six different single bipolar electrode codes was examined by 30 subjects using a balanced incomplete block experimental design. Codes with exponentially shaped transfer functions resulted in generally lower electrocutaneous tracking errors than codes utilizing hybrid-shaped transfer functions. Hybrid codes had a transfer function that was linear in the lower frequency range and exponential in the higher frequency range. Codes with a 2-100 Hz frequency range were interpreted better than codes with a 2-50 Hz frequency range. The use of pulse width compensation to maintain a more even level of stimulation intensity had a slightly negative effect on the subjects' abilities to cutaneously track the information signal.