Chapter 4 – Classical Conditioning: Mechanisms
• Important characteristics of the CS and US
– 1) Novelty of CS and US
• Latent Inhibition
– association account
– memory account
– Release from LI
• US preexposure
– 2) Intensity/saliency of CS and US
– 3) CS/US relevance (belongingness)
• Garcia and Koeling
– Bright Noisy Tasty water
– Belongingness
– 4) Stimulus Substitution
• Higher order conditioning
• Further evidence for stimulus substitution
– Jenkins and Moore (1973)
• Homeostasis
– Riccio
– Siegel

•
– We learn about novel stimuli more quickly than familiar.
• First noticed by Pavlov.
– If the dog had had heard the bell a lot before it was harder for it to learn the bell now predicted food

• Latent Inhibition (CS preexposure effect)
Phase 1
Phase 2
LI Group Forward control Random control
CS Nothing Nothing
CS  US CS  US unpaired CS and US
Test CS alone CS alone CS alone
Phase 1
Phase 2
Test
LI Group Forward control Random control bell nothing nothing bell  food bell  food unpaired bell and food bell alone bell alone bell alone

• Why are familiar stimuli less easily conditioned?
• 1) The associative interference theory
– Prior learning about the CS or US interferes with the animals ability to learn new things about the CS or US.
• Learned irrelevance or safety?
– The animals learn the CS is irrelevant or safe in phase 1
– The Bell doesn’t lead to anything good or bad
» Habituation
– Let’s apply to taste aversion
• phase 1
LI group sacch
CTA group Backward control nothing nothing
• phase 2 sacch  LiCl sacch  LiCl LiCl  sacch
• test sacch alone sacch alone sacch alone

• learned irrelevance or safety
– the LI group
• saccharin is “safe” in phase 1
• This “safe” learning makes it harder to learn that saccharin is now “unsafe”
– Input problem
– CTA group
• Didn’t learned saccharin is safe.
• neophobia
– which is confirmed

• 2) A memory interference theory of Latent Inhibition
– Perhaps LI occurs because animals have learned two things equally well
• The CS is safe
• The CS makes me Ill
• What happens at test?
– LI group
• memories compete
• “safe” and “bad”
– intermediate level of CR.
– CTA
• one memory
• “bad”
– stronger CR
– Backward group
• one memory
• “safe”
– least CR
• This is an output problem

•
–
• LI is the same as CTA group.
–conditioned responding increased
• why?
–Biological importance of memories?
»CS Safe?
»CS Dangerous?

• US preexposure effect
Phase 1
Phase 2
US preexposure Forward control Random control
US Nothing Nothing
CS  US CS  US unpaired CS and US
Test CS alone CS alone CS alone
Phase 1
Phase 2
Test
US preexposure Forward control Random control
Food nothing nothing bell  food bell  food unpaired bell and food bell alone bell alone bell alone

• CS and US Intensity and Salience
– We have covered this before
• louder or brighter CSs
• more flavorful or painful USs
– Can be manipulated indirectly
• Salt deprived rats
– taste aversions to a salty substance
– Learn quickly

• CS-US Relevance, or Belongingness
– Bright – Noisy – Tasty Water
• Garcia and Koeling (1966)
• Group 1 – bright noisy tasty  LiCl
• Group 2 – bright noisy tasty  sho ck test both groups with a choice between bright noisy tasty
• group 1 (LiCl) drink don’t drink
• group 2 (Shock) don’t drink drink

• this illustrates species-specific differences in preparedness to learn
– taste  illness
– sounds /sights  pain.
• Pigeons?
– use sight more than taste for foraging
• color and shape of seeds
– learn a visual cue (colored bead) goes with illness readily.
• Humans?
– spiders and snakes – shock
– Houses and flowers – shock

•
– The Stimulus Substitution model (Pavlov)
• The CS becomes a surrogate US
• This is why the CR and UR are typically the same
– Salivation/Salivation
• This is one explanation for how higherorder conditioning can occur.

• Higher-Order Conditioning (Second-Order) phase 1 phase 2
Exp. Group Control Group
CS1 (light)  US (shock) CS1 (light) /US (Shock) random
CS2 (tone)  CS1 (light) CS2 (tone) --> CS1 (light test CS2 (tone) alone CS2 (tone) alone
• Can you think of an example of higher order conditioning that we handle every day?

• Further evidence for stimulus substitution
– Different US’s produce different UR’s
• Food  salivation
• Shock  withdrawal and aversion
• Puff of air to the eye  eyeblink
– Jenkins and Moore (1973)
• even subtle differences in the US can affect the nature of the conditioned response.

• Pigeons
• GP 1
• Key light (8 s)  Grain
• What procedure is this?
GP 2
Key light (8 s) 
• CS, US, UR, CR?
CS, US, UR, CR?
• CR is pecking the key in both cases
– How the pigeons pecked the key depended on the US
– Food
• Peck like eating
• Rapid with beak closing when striking the key
– Water
• Peck like drinking
• Slower with beak open and swallowing behavior
Water

• Learning and Homeostasis: A Special Case of Stimulus
Substitution
– For our bodies to work well we often have to maintain physiological parameters within some acceptable limit.
• e.g., Body temperature (98.6 degrees)
• Walter Cannon
– Introduced term Homeostasis
• physiological mechanisms that serve to maintain critical aspects of the body within acceptable limits.
• What happens when we get cold?
– compensatory reaction
• Wouldn’t it be more efficient, if we could anticipate when we are going to get cold?
– Compensate ahead of time?

• Conditioned Cold Tolerance (Riccio et al.)
• CS, US, UR, CR?
• What if you tested them in a new room?

• Drugs and Conditioned drug effects.
– It is well known that people also become tolerant to the effects of a drug
– Could this tolerance also be context specific?
• Siegel
– injected rats with 5.0 mg/kg of morphine every day in the same room (context)
• Increased body temperature
• Decreased heart rate
• decreased sensitivity to pain
– Paw lick latency
– over time all of these responses decreased
• tolerance

• Was this tolerance the result of Pavlovian conditioning?
– How would you find out?
• test in a new environment
– paw lick latency went back up
– temperature increased
– heart rate decreased
• CS, US, UR, CR?

• tolerance appears to be at least in part conditioned
– body learns to compensate for the action of the drug in an attempt to maintain homeostasis.
• Drinking in bar at 10 pm
• Drinking at school at 10 am
• Heroin Addicts
– large tolerance in normal surroundings.
– take the same dose in a novel place
• Many OD patients reported taking drug in new place
• Siegel has shown that rats are more likely to die from high dose of a drug they are tolerant to
– If in new environment

• If Seigel is correct typical classical conditioning findings should apply to this situation.
– Extinction
• Repeated exposure to the environmental cues (CS) in the absence of morphine (US).
– This has been shown
• What should happen if an animal had repeated exposure to the testing environment before the drug was injected to the animal?
– Known as?

• Note - Conditioned Tolerance is usually demonstrated (tested) while presenting the US.
• using Novel CS
2 vs. Trained CS
– No tolerance in novel context
1
• Its not your typical test with CS alone
• Conditioned withdrawal effects
– The result of a more traditional test of Pavlovian
Conditioning
• CS alone
• Note – withdrawal effects are often opposite of drug effects
– Cocaine – Euphoria
• Withdrawal - Depression

• Rats trained with context  Morphine
– Test with context alone?
• Showed increased withdrawal
– Wet dog shakes
– Paw tremors
– Ear wipes
– Head shakes
– Body twitches
– What if withdrawal occurs in new context?
• Decreased withdrawal