Associative learning is the classic form of learning typified by 
Pavlov's dog experiments.  When a neutral 
conditioned stimulus (a stimulus that produces no natural response) is associated closely in time with a meaningful 
unconditioned stimulus (a stimulus that normally produces some natural response, called an 
unconditioned response) the animal will learn to respond to the once neutral stimulus as if it were the 
unconditioned stimulus.  This learned response is called a 
conditioned response.
Hebbian learning is an example of associative learning, which occurs at the cellular level. It essentially requires that two (or more) stimuli occur at or near the same time as one another. In Hebb, they must also occur in proximity (i.e., amongst 
neurons that are connected, or near enough to each other to affect, or be affected by, the other).
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