Second-order conditioning, also known as higher-order conditioning, is a process in classical conditioning where a previously neutral stimulus (NS) becomes a conditioned stimulus (CS) after being paired with an already established conditioned stimulus. This results in the neutral stimulus eliciting the conditioned response (CR) even without the presence of the original unconditioned stimulus (US).

Steps of Second-Order Conditioning:

1. First-Order Conditioning:
   • Unconditioned Stimulus (US): A stimulus that naturally elicits a response (e.g., food).
   • Unconditioned Response (UR): The natural response to the US (e.g., salivation).
   • Conditioned Stimulus (CS): A previously neutral stimulus that, after being paired with the US, elicits a conditioned response (e.g., a bell).
   • Conditioned Response (CR): The learned response to the CS (e.g., salivation to the bell).
2. Second-Order Conditioning:
   • New Neutral Stimulus (NS2): A new neutral stimulus is paired with the already established CS (e.g., a light paired with the bell).
   • Conditioned Stimulus 2 (CS2): After repeated pairings, the NS2 becomes a CS2, capable of eliciting the CR on its own (e.g., the light now causes salivation).

In summary, second-order conditioning occurs when a neutral stimulus becomes a conditioned stimulus through its association with an already established conditioned stimulus, allowing it to elicit the conditioned response independently.