Figure 1.

Experimental design. a, Electrical stimulation was delivered by an external neurostimulator through percutaneous leads to FINEs or C-FINEs implanted on the residual peripheral nerves of four transradial and three transtibial amputees. Stimulation consisted of trains of square, biphasic, charge-balanced pulses. b, Frequency estimation task. Three participants were asked to estimate the perceived frequency of an evoked percept by moving a slider along a horizontal bar. Stimuli varied in both stimulation PF and PW. c, Frequency discrimination task. Four participants judged which of two sequentially presented pulse trains was higher in perceived frequency, while ignoring any differences in perceived intensity. d, Quality description task. Six participants selected sets of words that described the quality of the evoked percept. Participants could select as many words as they wished to describe each stimulus.