Figure 3.

Just Noticeable Difference (JND) experiment. We measured subjects' ability to distinguish adjacent vibrotactile stimuli. Reference stimuli were chosen at six locations starting from the wrist (location 0) to the elbow (location 255). (A) Psychometric curves at three separate locations along the arm. The coloured circles correspond to average response data when binned into groups of 10 data points. The psychometric curves are Cumulative Gaussians fit to the raw data. (B)Sensitivity along the forearm can be plotted as a function of the success at distinguishing any two given stimuli. The 75% JND thresholds (black bars) suggest a region of stimulus indistinguishability (red shaded region). From this region we calculate the number of just-distinguishable stimuli, shown by the black blobs. This analysis indicates that approximately 12 distinguishable stimuli can be perceived along the forearm.