What is second-order conditioning (SOC)
Second-order conditioning is a form of associative learning in which, after a stimulus becomes conditioned through an initial step of association (first-order conditioning), it acquires the properties of an unconditioned stimulus and becomes the basis for a subsequent stimulus to become conditioned (second-order conditioning). A subsequent new stimulus does not need to be paired with the initial stimulus and can still generate similar results. Second-order conditioning is a type of higher-order conditioning.
SOC can be found in classical conditioning and operant conditioning.
In classical conditioning terms, an unconditioned stimulus can trigger an unconditioned response. When a neutral stimulus is repeatedly presented right before the unconditioned stimulus, it becomes a conditioned stimulus that can trigger the same response, now called a conditioned response.
Secondary conditioning occurs when these learning conditions are repeated twice, as follows1.
Phase 1 (1st order conditioning) – a neutral stimulus is followed by an unconditioned stimulus (US) and becomes a first-order conditioned stimulus (CS1) that can elicit a conditioned response (CR).
Phase 2 (2nd order conditioning) – a second neutral stimulus is followed by CS1. This second stimulus becomes the second-order conditioned stimulus (CS2).
Phase 3 – after the second phase, CS2 alone can elicit the same CR that CS1 can, even though CS2 has never been directly paired with the US.
Second-order conditioning examples
Second order conditioning in animals
Here is the training procedure Pavlov (1927) used on his dog2.
Phase 1 – Initial training involved pairing the sound of a metronome (CS1) with the presentation of food (US) to trigger salivation in the dog (CR).
Phase 2 – Further training was done to pair a black square (CS2) with the sound of a metronome to trigger salivation in the dog.
Phase 3 – Finally, the dog salivated at the sight of the black square, even in the absence of the metronome.
Second order conditioning in humans
Posttraumatic Stress Disorder (PTSD) is an example of second order conditioning in humans.
In PTSD, a traumatic event is the US, and patients’ fear response is the UR.
Phase 1 – During the trauma, environmental cues become a conditioned stimulus (CS1) through first-order aversive conditioning. For instance, if the patient saw a fearful face right before an accident, then the fearful face becomes CS1.
Phase 2 – Later, CS1 becomes associated with another environmental cue through SOC. The fearful face is associated with a knock on the door. Then the knocking becomes CS2.
Phase 3 – Afterwards, even though the traumatic experience and fearful faces are no longer present, the knocking may still trigger fear responses.
Models of SOC
Many theoretical models attempt to explain SOC. They can be categorized into four types based on the different kinds of associations formed and the nature of learning during SOC.
S-R learning model
CS2 and CR develop a direct connection when CS1 is present during second-order learning.
In a chain of association fashion, CS2 will evoke a CS1 representation, and CS1 will evoke the US representation, which will evoke CR.
A direct link between CS2 and US is established during the second-order training trials. Therefore, CS2 could activate the CR.
There is an association between CS1 and CS2 where CR emission is only due to the CS1 representation in CS2.
One special characteristic of conditioning in the second order is that extinction in a first-order stimulus does not necessarily lead to extinction in the second-order stimulus4.
After SOC has been established, extinction occurs if first-order CS is repeatedly presented without being followed by the US. However, even after the first-order association has been extinguished, the second-order CS persists more or less at the same magnitude.
The second-order association has not been affected by the first-order extinction5.
SOC in posttraumatic stress disorder
Patients suffering from PTSD often suffer for many years after the traumatic incident or the initial triggering cue is gone.
In PTSD, the trauma-related cues might obtain the properties of the original trauma over time to serve as an unconditioned stimulus. Second-order conditioning allows the fear beliefs to trigger fear-related responses such as panic attacks for years to come3.
The difficulty in extinguishing second-order Pavlovian conditioning may contribute to PTSD and the difficulty in stopping the adverse emotional reactions in this disorder.
- 1.Jara E, Vila J, Maldonado A. Second-order conditioning of human causal learning. Learning and Motivation. Published online August 2006:230-246. doi:10.1016/j.lmot.2005.12.001
- 2.Sahley C, Rudy JW, Gelperin A. An analysis of associative learning in a terrestrial mollusc. J Comp Physiol. Published online 1981:1-8. doi:10.1007/bf00612791
- 3.Wessa M PhD, Flor H PhD. Failure of Extinction of Fear Responses in Posttraumatic Stress Disorder: Evidence From Second-Order Conditioning. AJP. Published online November 2007:1684-1692. doi:10.1176/appi.ajp.2007.07030525
- 4.Davey GCL, McKenna I. The Effects of Postconditioning Revaluation of CS1 and UCS Following Pavlovian Second-Order Electrodermal Conditioning in Humans. The Quarterly Journal of Experimental Psychology Section B. Published online May 1983:125-133. doi:10.1080/14640748308400899
- 5.Rescorla RA. Simultaneous second-order conditioning produces S-S learning in conditioned suppression. Journal of Experimental Psychology: Animal Behavior Processes. Published online 1982:23-32. doi:10.1037/0097-7403.8.1.23