Fig. 5

Combined cutaneous location and intensity discrimination. Figure depicts the location of electrodes which evoked different hand sensations, as well as a confusion matrix showing the discrimination performance, and the overall accuracy relative to chance. Full descriptions of the percepts are presented next to the image of the hand and are abbreviated to the bold word in the confusion matrix. Confusion matrices are square, such that the correct answers lie along the diagonal. Asterisks over the bar plot indicates statistical significance with regards to the aggregate data (primary outcome measure). Asterisks overlaid on the confusion matrix indicate statistical significance with regards to an individual condition (secondard outcome measure with limited statistical power). Subject S5 discriminated among combinations of different cutaneous percept locations and intensities. Three median-nerve-USEA electrodes evoked cutaneous “pressure” percepts on D2, D3, and the palm, respectively. Three frequencies (35 Hz, 70 Hz, and 100 Hz) were used to encode three different intensities via each electrode. Sham trials were also included (no stimulation) for a total of ten classification categories. The subject correctly classified the combination in 15/30 trials (p < 0.0001, binomial test). In post-hoc analysis, we found that most of the subject’s success was attributed to accurate location discrimination (26/30 correct trials, p < 0.0001, binomial test for location classification independent of intensity classification, using a corrected critical value of α = 0.005). * = p < 0.05, ** = p < 0.01, *** = p < 0.001, **** = p < 0.0001; binomial test