Learning is an association between stimulus and

Behaviourist theories of learning (Pavlov's classical conditioning, Thorndike's connectionism, and Watson's stimulus-response psychology) define learning as the formation of a bond between a stimulus (S) -- any event that triggers activity -- and a response (R), the reaction that event produces. Repetition and reinforcement strengthen this stimulus-response connection, so the response becomes progressively more likely whenever the stimulus recurs.

In this statement, the blank names the second element of that S-R pair. Learning is therefore defined as an association between a stimulus and a response: Pavlov's dog learned to associate the bell (stimulus) with salivation (response); Thorndike's cat in the puzzle box associated pressing the lever (response) with escaping the box for a reward, given the box as the stimulus situation. Thorndike's Law of Effect explains that reinforcement strengthens exactly this stimulus-response bond, which is why later behaviourists describe learning as 'S-R learning'.

• Past experience names what a learner has already stored from earlier encounters -- a memory-based idea, not the specific reaction a stimulus provokes, which is what the S-R formula names.

• Behaviour is the broad, observable output of an organism in general; the S-R definition names a narrower, specific element -- the discrete reaction elicited by a stimulus -- not behaviour as a whole category.

• Animal names the experimental subject used to demonstrate stimulus-response learning (e.g. Pavlov's dogs, Skinner's rats and pigeons), not an element inside the stimulus-response definition itself.

The stimulus-response (S-R) bond is the defining feature of behaviourist learning theory, so the completed statement reads: learning is an association between stimulus and response.