Answer:
This conditioning is called second-order conditioning.
Explanation:
Second-order conditioning was first demonstrated by Pavlov, with experiments such as the one mentioned in the question. Second-order conditioning occurs when a conditioned stimulus, in this case the tick of the metronome, is paired with a conditioned response, in this case the salivation, and the relationship between the two is strong enough to produce a reliable conditioned response; then the conditioned stimulus can be paired with a second conditioned stimulus and eventually the second conditioned stimulus, in this case the black square, will cause the same conditioned response, the salivation.
