Immunization and facilitation produced by predictable and controllable aversive events alternating with different duration unpredictable and uncontrollable aversive events

T his investigation examined whether immunization to learned helplessness is more effective through predictable and controllable events alternating with inescapable and unpredictable events of different duration, than through experiences with only controllable and predictable events. Prior experience with intermittent success resulted in greater immunization than experience with consistent success. Forty-two male Wistar rats were distributed at random to one of the six groups (n = 7 each). In groups M-20, M-40, and M-80, uncontrollable and unpredictable episodes of shocks with three levels of duration were intermixed with controllable and predictable events: short mixed immunization, 20 trials; moderate mixed immunization, 40 trials; and long mixed immunization, 80 trials. Group C-U received immunization treatment with only controllable and predictable events; C-NT was the control group and received controllability training but with no uncontrollable and unpredictable footshock; and group NT-U received basic learned helplessness treatment. In the test phase, all the subjects were exposed to escape/avoidance training. The results demonstrated the greater efficacy of immunization in groups M-20 and M-40 (short and moderate mixed immunization), in terms of significant differences in latency of response relative to groups M-80 (long mixed immunization) and C-U ( standard immunization), while the behaviour of groups M-80 and C-U was similar. All immunization ( mixed and standard) groups presented a shorter latency than group NT-U ( no immunization). These data were discussed according to the "dual-expectancy hypothesis,'' the "interference hypothesis,'' the "anxiety hypothesis,'' and the "reactance theory".