SDT analysis of experimental thermal pain, with "signal" and "no-signal" being determined psychophysically.

In a signal-detection experiment, the effects of repeated pain stimulation and the induction of fear on pain thresholds and SDT parameters were studied. "Signal" and "no-signal" were not defined physically, but by means of an independent criterion as the primary sensations "pain" and "no-pain." First, the relationship between sensation levels for "phasic" (short stimulus, used in the SDT procedure) and "tonic" (longer stimulus, used in the criterion measurement) heat stimuli was determined in 14 subjects. It was quadratic (polynomial regression) and sufficient to define the distinction between "signal/pain" and "no-signal/no-pain." In the signal-detection experiment, a significant upward trend (adaptation) in threshold parameters, but no systematic change in the SDT parameters (discrimination ability and response bias) was found. Manipulation of anxiety by instructions caused unsystematic changes in discrimination ability. The procedure employed determines both the absolute strength of pain sensation and the ability to discriminate pain from no pain. These variables proved to be independent.