Figure 2: Psychophysical probability density functions of pain with and without stimulation.

Shown are all four patients' psychometric probability density functions. These curves represent the probability of pain at specific temperatures, and the circles represent the density of the probability based on experimental data. The pain threshold is the temperature with a 50% probability of the stimulus being painful. Each threshold is associated with a standard deviation, shown as a horizontal error on each curve. Patient 1 and Patient 4 showed no difference in pain thresholds when stimulation was on compared to off (Welch’s t-test). However, Patients 2 and 3 had a higher pain threshold with stimulation.