In order to test whether feigned pain responses would be inconsistent with the addition of sensory interference, electrical stimuli were delivered using a transcutaneous electrical nerve stimulation (TENS) device (Com-Tens; Apex Medical, Medfit, Finland) with two 3 x 3-cm flexible electrodes, set to a pulse width of 250 microseconds and pulse frequency of 100Hz. The intensity was adjusted for each patient so they would feel a nonpainful strong tingling sensation.
For the first experiment, participants were trained in WST and HPT measurement before testing to minimize the chances of learning effects during the testing. After the training session, researchers measured the participants’ WST and HPT with the thermal stimulator on the dorsal surface of the hand. Participants were then told to pretend that they were in a scenario in which they had to prove they were suffering from intense pain in order to receive financial compensation from an insurance company for pain-related disability.
The researchers calculated differences in °C between the first and fourth stimuli for WST and HPT to determine within-test trends of performance for each condition and used coefficient of variability (CV) as an index of consistency. The CV was defined as the ratio for the standard deviation to the mean of the 4 repeated measures of each threshold.
Among the 37 participants in the first experiment, 34 (91.9%) reduced their HPT and 3 increased their HPT when feigning. Neither the HPT variance (feigned: 1.56, CI = .74–2.39; sincere: 1.47, CI = .96–1.99; P = .87) nor CV (feigned: 2.45%, CI = 1.86–3.03; sincere: 2.41%, CI = 1.98–2.83; P = .93) was significantly different between conditions, suggesting that feigning did not affect the ability to perform in a repeatable manner, the researchers found.
For the second experiment, researchers included the electrical stimuli to study how it would affect sincere and feigned performance. They tested the hypothesis that a sensory interference would disrupt the repeatability of only the feigned but not the sincere performance.