A psychophysical analysis of experimential factors that selectively influence the affective dimension of pain

A psychophysical analysis was made of experiential factors that influence the affective but not the sensory-discriminative dimension of pain. Seven subjects made cross-modality matching responses to several dimensions of their experience. Before each stimulus, they matched line lengths to their experienced desire to avoid pain (significance) and to their perceived likelihood of avoiding it (expectation). After each stimulus, they matched line lengths to perceived sensation intensity (in some sessions) or to felt magnitudes of positive or negative feeling (in other sessions). Non-noxious (35, 42 degrees C) and noxious (45--51 degrees C) skin temperature stimuli were randomly interspersed during each experimental session. Changes in expectation were induced by preceding one-half of the noxious stimuli with a warning signal. The average responses of these subjects indicated that 45--51 degrees C noxious temperatures were felt as less unpleasant when preceded by a warning signal. In contrast, sensation magnitudes evoked by these same skin temperatures were unaffected by the warning signal. Thus, only the magnitudes of unpleasant responses are lowered by decreasing ones' expectation of avoiding pain. Analysis of individual responses revealed two distinct patterns of response changes following presentation of the warning signal. Four subjects retained the same general goal of avoiding pain and reduced their expectation of avoiding it. Their affective responses were less unpleasant during the warning signal. The remaining three subjects primarily altered their goals and not their expectations on signaled trials. Their affective responses were not modified by the signal. Subjects were instructed to arrive at their affective responses in two ways. In one session, they compared the outcome of each stmulation with what they wanted to happen (affect-result responses). In the other session, they simply focused on the pleasantness or unpleasantness of each sensation as it was experienced (affect-process responses). All subjects' affect-result responses were more positive (or less unpleasant) than affect-process responses. All of these results underscore the critical influence of expectations and the manner in which one evaluates sensations on affective responses to noxious stimulation.