Two hundred and sixteen male hooded rats, 140 days old, were shocked in a Campbell and Teghtsoonian learned-fear situation. Aversion thresholds were determined and different groups were exposed to constant voltage AC, matched impedance AC, constant current AC, and constant current DC. All sources, excluding constant voltage, caused freezing behavior up to a maximum intensity specific to the source. Results cast doubt on the concept of a single ideal shock for behavioral studies.
