Abstract: | Every one of the 8 Ss in this experiment showed lower heart rate in anticipation of a temporally uncertain UCS than he did during anticipation of a temporally certain one. Vigilance for uncertainty removing cues during UCS uncertain trials was offered as an explanation for the reduced heart rate of this condition. Previous investigations showing acceleration in heart rate under conditions of UCS temporal uncertainty were criticized, particularly with respect to the adequacy of the cardiac baseline employed. One unexpected and unexplained finding of this study was that 7 out of 8 Ss rated shocks as more painful when the UCS was certain than when it was uncertain. |