What Is Higher-Order Conditioning?
Higher-order conditioning (sometimes called second-order or higher-order Pavlovian conditioning) is a respondent conditioning process in which a new neutral stimulus (NS) is paired with an already-established conditioned stimulus (CS) rather than directly with an unconditioned stimulus (US). As a result of this pairing, the new stimulus also acquires the ability to elicit a conditioned response, even though it was never directly paired with the US.
This process was first demonstrated by Pavlov in his original conditioning experiments and has since been replicated across many species and response systems. Higher-order conditioning explains how stimuli that are far removed from primary biological events can nevertheless come to control emotional and physiological responses.
The Mechanism Step by Step
First-Order Conditioning
In standard (first-order) respondent conditioning, a neutral stimulus is paired with an unconditioned stimulus. For example:
- A tone (NS) is paired with food (US)
- Food elicits salivation (UR)
- After repeated pairings, the tone (now CS) elicits salivation (CR)
Second-Order Conditioning
Once the tone is an established CS, it can be used to condition a new stimulus:
- A light (new NS) is paired with the tone (established CS)
- The tone elicits salivation (CR)
- After repeated pairings, the light (now a second-order CS) also elicits salivation, even though it was never paired with food directly
Third-Order and Beyond
In theory, the process can continue to higher orders (pairing a new stimulus with the second-order CS), though each successive order typically produces weaker conditioning. In practice, third-order conditioning is difficult to demonstrate reliably in the laboratory, and higher orders are extremely rare. The conditioning tends to weaken with each remove from the original US.
Clinical Relevance to ABA
Understanding Complex Fear and Anxiety
Higher-order conditioning helps explain how fears and anxieties can spread to stimuli that were never directly involved in an aversive experience. A child who was bitten by a dog may develop a fear of dogs (first-order conditioning). If the dog was on a specific street, the child may also develop anxiety about that street (second-order conditioning). Over time, even hearing the name of that street or seeing it on a map might elicit mild anxiety (third-order conditioning). This chain of conditioning helps behavior analysts understand why some clients present with anxiety responses to seemingly unrelated stimuli.
Conditioned Reinforcers
Higher-order conditioning is closely related to the development of conditioned reinforcers. A stimulus that has been paired with an established conditioned reinforcer can itself become a conditioned reinforcer. This process explains how stimuli far removed from primary reinforcers (such as money, grades, or tokens) acquire their reinforcing properties through chains of conditioning. In token economy systems, the tokens function as conditioned reinforcers that were established through pairing with backup reinforcers, and the token board or point system may become a higher-order conditioned reinforcer through its association with the tokens.
Understanding Word Meaning and Emotional Responses to Language
Higher-order conditioning has been proposed as one mechanism by which words acquire emotional properties. If the word "fire" is paired with the sight and heat of actual fire (first-order conditioning), the word itself comes to elicit a mild fear response. Subsequently, a new phrase like "forest fire" could acquire emotional properties through its association with the already-conditioned word "fire" (second-order conditioning). This mechanism may complement the verbal behavior analysis of how language acquires its effects.
Relationship to Other Concepts
Sensory Preconditioning
Higher-order conditioning should be distinguished from sensory preconditioning, which involves a different temporal arrangement. In sensory preconditioning, two neutral stimuli (A and B) are paired first, and then one of them (B) is paired with a US. The result is that A also elicits the CR, even though A was paired with B before B had any conditioned properties. While both processes involve indirect conditioning, the order of events is different.
Stimulus-Stimulus Relations
Higher-order conditioning demonstrates that organisms learn relationships between stimuli, not just between stimuli and responses. The second-order CS acquires its properties through its relationship with the first-order CS, which in turn has a relationship with the US. This chain of stimulus-stimulus relations is a key feature of respondent conditioning that distinguishes it from simple stimulus-response learning.
Limitations and Considerations
Several factors limit the practical significance of higher-order conditioning:
- Weakness of higher orders: Each successive order produces weaker conditioning, and the effect may be difficult to detect beyond second-order
- Respondent extinction of the first-order CS: Presenting the first-order CS without the US during second-order conditioning can lead to extinction of the first-order CS, which then undermines the second-order conditioning
- Individual variability: Susceptibility to higher-order conditioning varies across individuals and species
- Context dependence: Higher-order conditioning may be more or less likely depending on the specific stimuli, timing parameters, and context
BCBA Exam Tips
Higher-order conditioning questions on the BCBA exam typically ask you to identify the process in a scenario or to distinguish it from other respondent conditioning phenomena. Key points to study:
- Higher-order conditioning pairs a NS with an established CS, not directly with a US
- The new CS acquires the ability to elicit a CR through its association with the existing CS
- Each successive order produces weaker conditioning
- Distinguish higher-order conditioning from sensory preconditioning (different temporal order of pairings)
- Understand the clinical relevance for explaining conditioned reinforcers and the spread of emotional responses