Figure 4

Measurement of the perception threshold with an example data from a subject. Step 1: The perception threshold was roughly estimated to be 1.1 mA, since 1.0 mA was the intensity last perceived and 1.2 mA was the one first perceived. Step 2: Seven intensities were chosen in the range of 0.8~1.4 mA. Three repetitions produced 21 stimuli. Step 3: The frequency of 'perceived' responses were calculated for each of the seven intensities. Step 4: The perception threshold was determined to be 1.06 mA by predicting the intensity that would be detected in 50% of trials (i.e., 1.5 times).