Conditioning to a compound CS and the observation of CS-elicited behavior in 1-trial simultaneous and 1-trial backward conditioning procedures

In three experiments, rats received a single simultaneous pairing of a 4-s conditioned stimulus (CS) and a 4-s grid shock unconditioned stimulus (US) in which the CS and US began together. The CS was either an element (tone, light, or noise) or a compound composed of two elements (tone + light or tone + noise). In a fourth experiment, rats received a single backward pairing of a 4-s CS and a 4-s grid shock US in which the CS began at US offset. The CS was either a tone or a tone + light compound. Freezing and the suppression of licking elicited by the CS provided evidence for excitatory 1-trial simultaneous and 1-trial backward conditioning to the element and to the compound CSs. There was no evidence of greater conditioning to the compound CSs as compared to either of their constituent elements. An analysis of a videotaped record of the behavior of the rats in Experiment 2 revealed somewhat less freezing to the light than to the tone, but no evidence of a defensive behavior unique to light. Thus the defensive behavior to CSs associated with aversive USs is freezing, regardless of CS modality