Determinants of Classical Conditioning

How fast and how strongly a conditioned response gets established depends on several identifiable factors. The first is the time relationship between the conditioned stimulus (CS) and the unconditioned stimulus (US). Four basic arrangements are possible: in simultaneous conditioning the CS and US are presented together at the same time; in delayed conditioning the CS begins before the US and the CS ends before the US ends; in trace conditioning the CS begins and ends before the US begins, leaving a time gap between them; and in backward conditioning the US actually precedes the onset of the CS. Of these, delayed conditioning has been found to be the most effective procedure for establishing a conditioned response, requiring the fewest trials. Simultaneous and trace conditioning do also lead to learning, but need more trials to succeed, while conditioning under the backward procedure is rare and generally weak.

The second determinant is the type of unconditioned stimulus used. Unconditioned stimuli are broadly of two kinds: appetitive stimuli (such as food, drink, or caressing) that produce pleasant, approach-type responses, and aversive stimuli (such as loud noise, bitter taste, electric shock, or a painful injection) that produce avoidance or escape responses. Conditioning built around appetitive stimuli tends to be slower, needing more trials, while conditioning built around aversive stimuli can be established very quickly — often in just one, two, or three trials — depending on how intense the aversive stimulus is. …