| Abstract: | ![]()
In Experiment I,Ss in each of four groups were given 8 shocks in either 8, 11, 16, or 32 trials, confounding probability with number of trials. Each trial was a countdown period of 30 sec, with an ITI of 30 sec. There were no shock probability effects using either heart rate (HR) or skin conductance (SC), with respect either to average within trial changes or to average pre-shock levels relative to rest. In every group after a large acceleration in Trial 1, HR subsided and stabilized; SC rose steadily throughout the session. In Experiment II, Ss in each of four groups were given either 5, 10, 15, or 20 shocks in 20 trials, confounding probability with number of shocks. In addition to the large HR acceleration in the first trial, there were in this case between-group differences in HR, which were a direct function of number and probability of shocks. Skin conductance did not discriminate the groups, though it rose in all groups both within and across trials. Experiment III, a partial replication of Experiment II, showed that the HR differences in Experiment II failed to repeat when the shock intensity was reduced; and SC no longer increased over trials. |
