Development of a paradigm for measuring somatic disturbance in clinical populations with medically unexplained symptoms.

OBJECTIVE: This study aimed to develop an experimental paradigm, using healthy controls, to measure change in tactile sensitivity and response bias for subsequent testing of patients with medically unexplained symptoms (MUS).
METHODS: Participants judged whether or not they detected a weak tactile pulse (presented in 50% of trials). Performance in two conditions (tactile pulses presented with or without a concomitant light) was compared using signal detection analysis to assess whether a task-irrelevant light can invoke the sensation of touch, even in its absence.
RESULTS: The results showed that the presence of a concurrent light significantly improved participants' detection of the tactile stimulus by 13.7% [t(18)=4.24, P<.001]. Also, more false alarms (perceiving that the touch was present when it was not) were made when the light was present [t(18)=2.10, P=.05]. Although differences in sensitivity between the light conditions were not significant [t(18)=1.14, P=.268], participants were more likely to report a touch, regardless of whether a touch was presented or not, in the light-present condition [t(18)=-3.84, P=.001].
CONCLUSION: When discriminating weak vibration pulses on the finger from no stimulation, a simultaneous light was capable of creating the sensation of touch, even when it was not present. The findings of this research will be of interest to those studying psychosomatic disorders or MUS, where patients experience physical symptoms without an identifiable organic cause. This paradigm provides an experimental measure of such distortions in perception, which may elucidate underlying mechanisms of action.