Final answer:
Discrimination in learning refers to an organism's ability to recognize and respond differently to similar but distinct stimuli, as explained through classical conditioning examples like Pavlov's dogs.
Step-by-step explanation:
In the context of learning, discrimination is defined as the ability to recognize and respond differently to similar but not identical stimuli. This is an important concept in psychology, particularly within the scope of classical conditioning. An example of this would be an animal, such as one of Pavlov's dogs, learning to respond only to a specific sound that predicts food, while disregarding other similar sounds that do not lead to a reward. Hence, the correct answer would be "D. The ability to withhold a behavioral response except in the presence of specific stimuli" as it specifically describes the learning mechanism where an organism recognizes and distinguishes between different stimuli and thereby modifies its behavior.