Final answer:
Pavlov's discovery that the sound of footsteps had an effect on his dogs was a result of classical conditioning. The sound of the footsteps became a conditioned stimulus that elicited a conditioned response of salivation.
Step-by-step explanation:
Pavlov discovered that the sound of his co-workers' footsteps had an effect on his dogs through classical conditioning. By pairing the sound of footsteps with the arrival of food, Pavlov's dogs eventually started salivating at the sound of the footsteps alone. This demonstrates that the sound of the footsteps became a conditioned stimulus that elicited a conditioned response of salivation in the dogs.