Abstract
Subjects waited for 30-sec. countdown periods for shocks of varying probability of occurrence, 0%, 50%, or 100%, while heart rate, eye blink activity, and gross movement were recorded. If shock was anticipated at all, heart rate and blink activity were significantly higher than when it was not, but there was no difference associated with uncertainty, i.e., between 50% and 100%. Gross movement did not covary with the other measures. Heart rate was uniquely elevated on the first trial.