Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)



Committee Chair(s)

Carl D. Cheney


Carl D. Cheney


Richard B. Powers


Karl R. White


Gerald R. Adams


The safety signal hypothesis suggests that during the absence of stimuli predicting impending shock, the organism is not fearful. The stimuli which predict the absence of shock are therefore called safety signals. The purpose of the present study was to investigate some critical properties of safety signals. Such stimuli in an avoidance or escape situation, according to the opponent process model, are expected to acquire hedonic value opposite to shock.

This study examined differences in conditioning variables between safety signals predicting different intensities of shock, and between safety signals present in procedures using predicted shock, and procedures using unpredicted shock. Additionally, the effects of inescapable unpredicted shock with no safety signals present were examined.

The general procedure involved exposing pigeons to aversive Pavlovian conditioning and subsequently autoshaping these birds to stimuli which had predicted safety in the aversive situation. Dependent measures included trials to acquisition of the autoshaped response and subsequent rate of keypecking.

In the six experimental groups, pigeons were repeatedly and inescapably shocked at either 30 or 90 volts. Each individual 0.5 sec shock was (a) predicted by a specific stimulus or (b) not predicted. Additionally and explicitly unpaired with the shock, a safety signal was presented. For each voltage level, a control group was repeatedly shocked with no stimuli presented at any time.

Control groups were included which (a) received no aversive conditioning, (b) were autoshaped to a stimulus which had previously predicted shock, (c) received the aversive conditioning, and (4) were exposed to various stimuli but received no aversive reinforcement.

The principal finding was that preexposure to strong shock resulted in delays in response acquisition during subsequent autoshaping. This suggests that the learned helplessness hypothesis obtains with classically conditioned responding. Additionally, the importance of shock-alone control groups in the study of transfer effects is critical. Due to the lack of statistical power, the study was not definitive regarding the nature of safety signals or appetitive-to-appetitive transfers. Statistically significant differences were only found on acquisition measures, and no such differences were found on performance measures.



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