Find the odd one out.

Theories of transfer of training explain how learning gained in one situation carries over and applies to a new but related situation. Well-known accounts in educational psychology include Thorndike's theory of identical elements, Judd's theory of generalization, and Harlow's theory of learning to learn -- each proposes a specific mechanism for how earlier learning transfers to later learning.

• Theory of identical elements (Thorndike): transfer happens when the original task and the new task share common stimulus-response elements.

• Theory of generalization (Judd): transfer happens when a learner abstracts a general principle from one task that then applies to structurally similar new tasks.

• Theory of learning to learn (Harlow): repeated practice on a series of similar problems builds a general learning strategy (a "learning set") that carries over to new but related problems.

All three describe a mechanism of transfer between learning tasks. Drive reduction theory, by contrast, is a theory of motivation: it explains behaviour and learning as driven by the reduction of biological drives -- hunger, thirst, and similar physiological needs. It proposes no mechanism for how learning in one task transfers to another task.

Since the theory of identical elements, the theory of generalization, and the theory of learning to learn each name a specific mechanism of transfer of training, while drive reduction theory names a motivational account of learning with no transfer mechanism, drive reduction theory stands apart from the group.