Three experiments are reported. Experiment 1 indicated that the rat becomes more thigmotactie and immobile following shock compared with noshock conditions. Experiment 2 demonstrated that when two groups of subjects were required to make comparable, but different, avoidance responses, the group whose avoidance response was more closely related to the subjects' species-specific defensive behavior was acquired at a faster rate. The last experiment indicated that the differences in the acquisition of the avoidance responses in Experiment 2 were not due to differences in operant rates for the two responses per se, since acquisition of these same two responses was similar under appetitive motivation.

Seven experiments are described in which rats were trained on an avoidance response (R a ) either with or without the normal CS4ermination contingency. Lack of this contingency was found to impair acquisition of R a in most but not all situations. In situations where the impairment was found, it was largely overcome by the introduction of an informational or feedback stimulus contingent upon R a . The results lead to an interpretation which makes the amount, and kind, of stimulus change produced by R a the most important factor in avoidance learning. The OS-termination contingency is interpreted as being merely one kind, and a relatively ineffectual kind, of stimulus change.

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Rats were trained to avoid shock on a Sidman schedule in a shuttle apparatus; then they were tested with a probe stimulus that in a Pavlovian session for different groups signalled shock. or absence of shock. The danger signal increased the rate of avoidance responding and the safety signal decreased it. Two control procedures are compared.Several investigators have reported that fear conditioned by Pavlovian procedures can affect instrumental behavior (Hammond, 1966(Hammond, , 1967Rescorla & LoLordo, 1965). The procedure involved in these studies is to establish a conditioned fear signal (CS+) by explicitly pairing a signal with electric shock and then looking for facilitation by CS+ of a previously learned avoidance response. Alternatively, fear conditioning can be shown by the suppression of appetitive behavior by CS+ in a CER situation.A related procedure involves the presentation of a signal (CSl which explicitly predicts the nonoccurrence of shock and then looking for a suppression of avoidance responding in the aversive case, or an enhancement of response 'rate in the appetitive CER case whenever the CS-is presented. On the assumption that both CS+ and CS-effects are genuine, Rescorla (1967) has recommended a control procedure with a random CS-US pairing which, presumably, allows the CS to gain no associative control over the behavior since it consistently predicts neither the occurrence nor nonoccurrence of shock.There is some reason, however, to doubt the validity of Rescorla's assumpti~ns. The present experiment is concerned with whether Pavlovian training is given in a situation other than the test situation. Are the same effects obtained when S is a rat rather than a dog? Do the effects occur when a control other than Rescorla's random control procedure is used? Do the danger signal and safety signal effects appear when appropriate allowance is made for possible sensitization effects?Subjects. The Ss were 24 female Long-Evans rats approximately 110 days old at the beginning of the experiment.Apparatus. The shuttle apparatus was 36 in. x 5 in. high with metal walls. The floor was 3/8 in. stainless steel bars spaced on I·in. centers. A 2·in.barrier. located in the center of the box. had two parallel 1/8.in. stainless steel bars wired to a 120 V source through 250 K resistance across its top. Responses were detected by a photocell located 1·3/4 in. above the barrier.The Pavlovian conditiOning apparatus was a IO-in. square box with a grid floor similar to the shuttle box floor and metal wa1Is which were included as an element in the grid floor.Shock was provided to the apparatus by a Grason-Stadler shocker-scrambIer. model EI064GS. All programming and recording was done by appropriate electronic equipment isolated from the apparatus.Procedure. AD Ss were given frye training sessions with a Sidman procedure in the shuttle apparatus with an R-S interval of 30 sec and an s.s interval of 5 sec. Shock intensity was 1.25 rnA and shock duration was .25 sec. Each session lasted until S had made 300 responses.Fol...

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