Second-order conditioning
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In classical conditioning, second-order conditioning or higher-order conditioning is a form of learning in which a stimulus is first made meaningful or consequential for an organism through an initial step of learning, and then that stimulus is used as a basis for learning about some new stimulus. For example, an animal might first learn to associate a bell with food (first-order conditioning), but then learn to associate a light with the bell (second-order conditioning).

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Third order conditioning can then follow with a further stimulus being added and the response elicited can be weak. Also known as shaping behavior. Often related to B. F. Skinner's studies with pigeons. Another example would be Skinner first conditioned a pigeon to walk up to a ball, then conditioning it to touch the ball with its beak. He would thus use a second-order to shape the animal's behavior. Often used with biological predispositions.

In Fear Conditioning

Karim Nader and Joseph LeDoux showed that in building an associative fear conditioning chain, such as CS₂ --> CS₁ --> US, extinction of freezing responses to the first-order stimulus (CS₁) leads to responding impairments in CS₂, but extinction of the second-order stimulus (CS₂), does not have any effect on CS₁.

They also examined the effect of activation (memory retrieval) on such an associative chain. Results demonstrated that protein synthesis inhibition after exposure to a single CS₁ impairs responses to both CS₁ and CS₂, but protein synthesis inhibition after exposure to a single CS₂, only disrupts CS₂ and leaves CS₁ freezing intact. Therefore, it is believed that when the first-order association is directly activated, it is placed into a labile state (as we would expect from reconsolidation research) which may have an impact on dependent associations. However, when the first-order association is only indirectly activated (through the associative chain), it appears that there is not sufficient stimulation to kick off cellular processes which would place it in a labile state, so it remains fixed.¹

References

1. ^ Debiec, J., Doyere, V., Nader, K., LeDoux, J.E. (February 28, 2006). Directly reactivated, but not indirectly reactivated, memories undergo reconsolidation in the amygdala. PNAS, Volume 103, Number 9, 3428-3433.