Final answer:
The statement that the contingency between a conditioned stimulus (CS) and a conditioned response (CR) may be formed in one trial is true, as classical conditioning can vary in the number of trials needed for an association to be made.
Step-by-step explanation:
The correct statement regarding the contingency between a conditioned stimulus (CS) and a conditioned response (CR) is that the contingency may be formed in one trial or may take many trials. Classical conditioning shows that a CS, which initially does not elicit any particular response, can, after being paired with an unconditioned stimulus (UCS), eventually elicit a conditioned response (CR). The response that the CS elicits after conditioning is due to its association with the UCS. For instance, in Pavlov's experiments with dogs, the sound of a tone paired with meat powder led to dogs salivating (CR) at the sound of the tone alone, which became the CS. The frequency of trials needed for this association to be made can vary.
Robert Rescorla's research demonstrated that the predictiveness of the CS in signaling the UCS influences the strength of the conditioned association. This means that if a CS consistently and reliably predicts the UCS, the association between them can be learned more quickly, sometimes even in one trial. Therefore, the statement that contingency between a CS and a CR always takes many trials to form is not true; it can occur quickly, depending on various factors, including the strength of the UCS and the consistency of the pairing.