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

• CS and US Novelty –  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)

LI Group Forward control Random controlPhase 1 CS Nothing NothingPhase 2 CS US CSUS unpaired CS and USTest CS alone CS alone CS alone

 

LI Group Forward control Random control Phase 1 bell nothing nothing Phase 2bell food bell food unpaired bell and food Test 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

LI group CTA group Backward control• phase 1 sacch 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

• Release from LI (Kraemer & Spear, 1992)– Instead of testing right away wait for

21 days• LI is the same as CTA group.

–conditioned responding increased• why?

–Biological importance of memories?»CS Safe?»CS Dangerous?

• US preexposure effect

US preexposure Forward control Random controlPhase 1 US Nothing NothingPhase 2 CS US CSUS unpaired CS and USTest CS alone CS alone CS alone

 

US preexposure Forward control Random control Phase 1 Food nothing nothing Phase 2bell food bell food unpaired bell and food Test 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 shock

test both groups with a choice betweenbright 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

• What determines the nature of the Conditioned Response?– 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 higher-order conditioning can occur.

• Higher-Order Conditioning (Second-Order) Exp. Group Control Group

phase 1 CS1 (light)US (shock) CS1 (light) /US (Shock) random

phase 2 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 GP 2• Key light (8 s) Grain Key light (8 s) Water

• What procedure is this?

• 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

• 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 CS2 vs. Trained CS1

– No tolerance in novel context• 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