- What is trace conditioning
- Why is it called trace
- Length of stimulus-free interval
- Trace vs. delay conditioning
- Trace in the brain
- Trace fear conditioning
Despite being one of Pavlov’s lesser-discussed discoveries, trace conditioning is an everyday phenomenon observable in real life. Most people have experienced it first-hand themselves.
What is trace conditioning
Trace conditioning is a type of classical conditioning in which after a neutral stimulus (CS) is presented, a temporal gap follows before an unconditioned stimulus (UCS) appears to evoke a response. When the sequence is done repeatedly, it becomes associative learning. The neutral stimulus becomes a conditioned stimulus. Presenting the conditioned stimulus alone can trigger the same response, now called a conditioned response.
In classical conditioning, also known as Pavlovian conditioning, a neutral stimulus is presented with an unconditioned stimulus repeatedly to become a conditioned stimulus to trigger the same response. This form of classical conditioning is also called delay conditioning1.
Why is it called trace
According to Pavlov, an association between CS and UCS cannot exist without trace retention (associative memory, training, etc). In trace conditioning, a temporal gap exists after CS removal and before UCS introduction.
Despite neither stimulus exists within the same space at the same time, the brain forms an association between the two. This association relies on the brain’s ability to maintain a trace memory. Hence, this phenomenon is termed trace conditioning2.
Pavlov’s salivating dog
The bell rings then it stops. A few seconds later, food is introduced. The dog then salivates upon seeing the food. After a few days of repeating this practice, the bell’s ringing sound alone will make the dog salivate3.
Unconditioned stimulus: food
Conditioned stimulus: bell ringing
Conditioned/unconditioned response: salivation
Garage open, Dad comes home
A child gets excited every time she hears the garage door open because she knows that a few seconds later, her Dad will come through the door. The garage opening sound signifies her Dad’s return.
Unconditioned stimulus: Dad comes through the door
Conditioned stimulus: garage opening sound
Conditioned/unconditioned response: the child is happy
Seeing an Amazon delivery truck and receiving a gift
You see the Amazon delivery truck turning the corner and you feel excited because you know that a minute later, the delivery person will hand you a package which is often an electronic gadget you’ve been waiting for.
Unconditioned stimulus: Amazon delivery truck
Conditioned stimulus: receiving an Amazon package
Conditioned/unconditioned response: excited to try the new gadget
Length of stimulus-free interval
In trace conditioning, there is a gap period between the appearance of the unconditioned and conditioned stimuli. The interval functions can be anywhere from a few seconds to many minutes long.
In Pavlov’s study, he noted that as the trace interval, the period between CS offset and US onset, increased, the strength of the conditioned response decreased.
A longer stimulus-free gap may make it harder to form an association between the two stimuli4.
Trace conditioning vs. delay conditioning
The key difference between trace and delay conditioning is that presentation of the neutral stimulus and the unconditioned stimulus are separated in time in trace conditioning but not in delay conditioning. The UCS and CS must exist as distinct events in time. They cannot occur consecutively5.
The brain draws an association between the stimuli after conditioning to trigger a similar reaction. However, these two conditionings draw upon different parts so the brain and result in different properties in the conditioned result.
In general, delay-conditioned learning is faster and stronger than trace-conditioned one6.
Trace conditioning in the brain
Trace and delay conditioning are two distinct forms of learning. They involve different neural circuits and obey different regularities
Although both types of conditioning rely on the amygdala, only trace learning appears to involve the hippocampus and medial prefrontal structures in the brain7.
The pairing in trace conditioning appears to be dependent on an intact hippocampus that can retain a trace of the CS. The brain then fills in the gap and draws an association with the UCS despite the non-stimulus periods8.
Trace fear conditioning
In fear conditioning, a neutral stimulus is paired with a feared object or event. The conditioning can take the form of trace or delay conditioning.
Although trace learning takes longer and more repetitions to form, it is more resistant to extinction. Thus, an individual who has been trace-fear conditioned may be more difficult to treat, and further research is needed9.
- 1.Pavlov IP. Conditioned reflexes: An investigation of the physiological activity of the cerebral cortex. ANS. Published online June 1, 2010. doi:10.5214/ans.0972-7531.1017309
- 2.Raybuck JD, Lattal KM. Bridging the interval: Theory and neurobiology of trace conditioning. Behavioural Processes. Published online January 2014:103-111. doi:10.1016/j.beproc.2013.08.016
- 3.Kamin LJ. Trace conditioning of the conditioned emotional response. Journal of Comparative and Physiological Psychology. Published online April 1961:149-153. doi:10.1037/h0045611
- 4.Beylin AV, Gandhi CC, Wood GE, Talk AC, Matzel LD, Shors TJ. The Role of the Hippocampus in Trace Conditioning: Temporal Discontinuity or Task Difficulty? Neurobiology of Learning and Memory. Published online November 2001:447-461. doi:10.1006/nlme.2001.4039
- 5.Schneiderman N. Interstimulus interval function of the nictitating membrane response of the rabbit under delay versus trace conditioning. Journal of Comparative and Physiological Psychology. Published online 1966:397-402. doi:10.1037/h0023946
- 6.Bangasser DA. Trace Conditioning and the Hippocampus: The Importance of Contiguity. Journal of Neuroscience. Published online August 23, 2006:8702-8706. doi:10.1523/jneurosci.1742-06.2006
- 7.McEchron M, Bouwmeester H, Tseng W, Weiss C, Disterhoft J. Hippocampectomy disrupts auditory trace fear conditioning and contextual fear conditioning in the rat. Hippocampus. 1998;8(6):638-646. doi:8.Carter RM, Hofstötter C, Tsuchiya N, Koch C. Working memory and fear conditioning. Proc Natl Acad Sci USA. Published online January 27, 2003:1399-1404. doi:10.1073/pnas.03340491009.Sehlmeyer C, Schöning S, Zwitserlood P, et al. Human Fear Conditioning and Extinction in Neuroimaging: A Systematic Review. Gendelman HE, ed. PLoS ONE. Published online June 10, 2009:e5865. doi:10.1371/journal.pone.0005865