Answer:
Exciting athletes.
Explanation:
In psychology, the term classical conditioning refers to a form of learning in which a stimulus that triggers a natural answer by itself (unconditioned stimulus and unconditioned response) is paired with another stimulus that originally doesn't trigger any answer (neutral stimulus) but, after some repetitions, the answer evoked by the first stimulus starts to show up by presenting the originally neutral stimulus. Then, this answer is known as the conditioned response and the neutral stimulus has become a conditioned stimulus)
In this example the companies are pairing the logos which originally don't trigger any answer (and therefore are the neutral stimulus) to exciting athletes (which trigger a natural answer of excitement and thus are the unconditioned stimulus) in order that you get excited when you see the logo and buy the shoes. So, the answer evoked by the exciting athletes (unconditioned response) starts to show up when you just see the logo (neutral stimulus). Thus, in this scenario, the unconditioned stimulus (the one that triggers an answer by itself) would be the exciting athletes.
