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Classical Conditioning

Classical conditioning is important partly because it is the most primitive and basic form of learning. . It occurs even in animals with very rudimentary nervous systems, like the Aplysia or sea slug, a fist-sized invertebrate shown below.


An Aplysia, courtesy of Tom Capo of the University of Miami

Despite the basic simplicity of classical conditioning, beginning students often emerge from a unit on classical conditioning with a remarkably fuzzy understanding of it. Perhaps the antique terminology is at fault. Students' eyes glaze over when confronted with terms like conditional stimulus, unconditional stimulus, unconditional response, and conditional response. However, we are stuck with the old labels. If they bother you, ignore them for a while, and concentrate instead on understanding classical conditioning on an intuitive level. Later you can learn the labels.

Classical conditioning: What is it?

How might a sea slug make a simple anticipatory response?

Classical conditioning is a very simple form of learning. (It must be, if a sea slug can do it.) Classical conditioning happens when a stimulus the animal can identify (such as an odor in the water) is followed by a biologically significant event (such as the appearance of food). After several such pairings, the animal learns the connection. The next time the stimulus occurs, the animal acts like it expects the same event. That is, it makes an anticipatory response. If it is an Aplysia, maybe it extends its feeding tube.

What is the "rule" underlying classical conditioning?

This is not rocket science. Creatures do not need much of a nervous system to notice that when stimulus A happens, event B happens next. With a few neurons the sea slug can be really clever and make a response that prepares it for event B. The rule is, "Whenever you notice A, prepare for B." That is classical conditioning: an anticipatory biological response.


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