Sources of uncertainty and psychophysiological state changes under conditions of noxious stimulus anticipation.

The main aim of the experiment was to compare the effect of the two variables (regarded here as different sources of subjective uncertainty) - probability of stimulus occurrence and ambiguity of the message about this probability - upon changes in heart rate (HR) and skin resistance (SR) during anticipation of a noxious stimulus. Three other independent variables - the type of stimulus (shock vs. sound), repetition of trials (two series of trials), and time-within-trial - were controlled as well. Results indicate that ambiguity as compared to probability has a more pronounced effect upon SR changes. Effects of the two variables upon HR changes are not significant. Moreover, in the shock group, the effect of repetition of trials was found to have a habituation effect for HR changes and a dishabituation effect for SR changes.