<P> Second - order or higher - order conditioning follow a two - step procedure . First a neutral stimulus ("CS1") comes to signal a US through forward conditioning . Then a second neutral stimulus ("CS2") is paired with the first (CS1) and comes to yield its own conditioned response . For example: A bell might be paired with food until the bell elicits salivation . If a light is then paired with the bell, then the light may come to elicit salivation as well . The bell is the CS1 and the food is the US . The light becomes the CS2 once it is paired with the CS1 . </P> <P> Backward conditioning occurs when a CS immediately follows a US . Unlike the usual conditioning procedure, in which the CS precedes the US, the conditioned response given to the CS tends to be inhibitory . This presumably happens because the CS serves as a signal that the US has ended, rather than as a signal that the US is about to appear . For example, a puff of air directed at a person's eye could be followed by the sound of a buzzer . </P> <P> In temporal conditioning, a US is presented at regular intervals, for instance every 10 minutes . Conditioning is said to have occurred when the CR tends to occur shortly before each US . This suggests that animals have a biological clock that can serve as a CS . This method has also been used to study timing ability in animals (see Animal cognition). </P> <P> In this procedure, the CS is paired with the US, but the US also occurs at other times . If this occurs, it is predicted that the US is likely to happen in the absence of the CS . In other words, the CS does not "predict" the US . In this case, conditioning fails and the CS does not come to elicit a CR . This finding--that prediction rather than CS - US pairing is the key to conditioning--greatly influenced subsequent conditioning research and theory . </P>

The period in conditioning during which a response is reinforced