L3 Blocking Effect and CS Pre-exposure (PSYC2050)

The Blocking Effect & Hidden Assumptions

• Equipotentiality means any stimulus can be paired with any response
• Contiguity means the more two stimuli are paired, the associate will be stronger
• Pairing light with the shock did not lead to conditioning
• The control group and blocking group had the noise+light/shock pair the exact same amount of times

CS Pre-exposure (Latent Inhibition)

• Latent Inhibition is related to CS Pre-exposure
• Pre-exposure affects conditioning
• CS pre-exposure slows subsequent conditioning for that CS compared to a new stimulus
• One possible explanation for this is Habituation, another is Conditioned inhibition
• CS pre-exposure is context specific
• Habituation is not context specific, it occurs regardless of the context
• CS pre-exposure retards (slows) learning
• CS pre-exposure fails the summation test
• Evidence shows CS-pre-exposure/ latent inhibition is not the same as inhibitory conditioning because when a pre-exposed CS is presented along with an excitatory stimulus, conditioned responding is not reduced compared to the excitatory stimulus alone

Classical Conditioning Phenomena: Generalisation-Discrimination

• In the context of generalisation in classical conditioning, Little Albert was conditioned to fear rabbits.
• He then also feared a black rabbit and Santa Claus (white fluffy beard)
• Classical Conditioning does generalise
• Generalisation works strongest with similar stimuli
• Discrimination does not last after extensive training trials
• Each exposure to CS1-US refines association
• Provided CS2 or CS3 are not ever presented with US, and reduced responding to CS2, CS3 happens over time
• There are evolutionary benefits, where prey animals would pay to not waste energy comparing African wild dogs when they are resting

Basic Principles of Generalisation and Discrimination

• For generalisation, other (similar) stimuli may also produce the CR
• The more similar to the original CS, the more likely it is to elicit the CR
• For discrimination, early on during acquisition, generalisation may cause the learner to respond to a variety of stimuli
• As learning continues, the organism learns which CS seems to be best associated with US (they discriminate)

Research and Theory in Conditioning

• Research finds that trace conditioning is less effective than short-delay conditioning
• Theory explains why trace conditioning is less effective than short-delay conditioning

Models in Psychology

• A model is a formal attempt to explain a wide body of research
• Models make predictions, and predictions can be tested
• E.g. Some models are mathematical: ΔV = αβ (λ −V)

Developing a Formal Model of Classical Conditioning

• Models must be independent of conditioning procedure
• Models must generate testable predictions
• The Rescorla-Wagner Model explains how organisms learn the prediction of the US
• The Mackintosh (1975) Model states cues (e.g., aCS) that signal reliable consequences command more attention than nonpredictive cues
• The Pearce & Hall (1980) Model states most attention is paid to cues whose consequences are uncertain

The Rescorla-Wagner Model (1972)

• The level of conditioning is a result of an internal comparison between expected strength of the US vs actual strength of the US
• Expectation is based on prior experience with the US (i.e., previous trials)
• Strength of the US is fixed (e.g., mild shock)
• ΔV (Change in associative value of CS)
• α (salience of the CS)
• β (strength of the US to promote conditioning)
• λ (Magnitude of associative value that can be conditioned for CS; limit of learning)
• V (Current associative value of CS (expectations about the CS-US association/CS value))
• It is called surprisingness of the US
• Previous models assumed that a CR gets stronger the more a CS is paired with a US, the Rescorla Wagner model basically assumes that a CR gets stronger if the CS-US pair is SURPRISING

Rescorla-Wagner & the Blocking Effect

• Kamin (1968) found that rats ignored a light if the light happened at the same time as a noise that they had previously learned predicted a shock
• This is the blocking effect, and it violates the frequency principle
• Rescorla-Wagner explains this by saying that the light doesn’t change how surprised the rat is at being shocked.
• The rat ignores the light because it already expects the shock to happen because of the noise

Rescorla-Wagner, & Superconditioning

• Superconditioning occurs when a previously learnt stimulus is combined with a new stimulus
• Rescorla-Wagner model also predicted there would be superconditioning (the opposite of blocking).
• In superconditioning, the old stimulus is inhibitory and the combination is excitatory leading to a surprise that a US is presented
• The organism develops an association between the new stimulus & the excitatory CS

Attentional Models of Classical Conditioning

• The Rescorla-Wagner model is not perfect
• Has difficulty explaining/predicting CS Pre-exposure (Latent inhibition)
• Mackintosh (1975) postulates that organisms pay more attention to stimuli that, via learned experience, prove to be strong predictors of important events
• Blocking is due to ignoring second CS in this model
• Pearce and Hall (1980) theorise that organisms pay less attention to stimuli that, via their experience, prove to be strong predictors of important events so blocking is due to not attending to all compound trials

Taste Aversion

• In typical classical conditioning, acquiring a CR requires dozens of trials associating the CS and the US
• In typical classical conditioning, long-delay conditioning (more than a few seconds) is less effective
• One can acquire taste aversion in one single trial
• The time between eating something and getting sick can be as long as 24 hours

Classical Conditioning Phenomena: Garcia Effect

• The Garcia Effect is also known as Preparedness
• There are a question if all associations are learned equally
• Equipotentiality implies every CS has the same potential to be associated with a US (Pavlov)
• Garcia & Koelling (1966) showed this assumption does not hold, that some associations are learned faster than others (laps/min = learning rate)

Classical Fear Conditioning: Contemporary Research

• A CS+ was paired with a US shock; the other type of stimulus was not paired with shock (CS-)
• This is differential conditioning paradigm
• Extinction used SCR (skin conductance response) as a CR
• Rapid extinction happened more to mushroom in fear conditioning than snakes, because of innate learning that snakes are dangerous and need of immediate attention

Classical Conditioning and Racial Attitudes in Olsson, Ebert, Banaji, & Phelps (2005)

• The role of social groups in the persistence of learned fear, Science, 309, 785-787
• Experiment 1: participants viewed images of fear-relevant (a snake and a spider) and fear-irrelevant (a bird and a butterfly), which were the CS+ or CS-
• mild shock was the US, and UR and CR was SCR
• Experiment 2: Black and White (American) participants viewed images of unfamiliar Black and White males, which were the CS+ or CS-
• Experiment 1 SCR difference = difference in CR to the CS+ and CS-
• Fear conditioning to outgroups was more attenuated for those participants who had more interracial romantic partners

Classical Conditioning in Everyday Life: Heroin Addiction

• Many heroin users overdose and die after taking a fairly usual when in an unfamiliar environment
• Siegel et al. (1982) argued that this is because the body’s tolerance to heroin is influenced by classical conditioning
• There are usually similar environmental cues when heroin is taken.
• The endocrine system associates these cues with taking heroin, and ramps up the tolerance response so if those cues are not present, the body isn’t as prepared to tolerate heroin so an overdose is more likely
• For Siegel's Experiment, the training involved the Experimental group recieving Heroin in room A, Placebo in room B, and the Control group recieving Placebo in both rooms
• For the Test, all the groups recieved a Higher dose of heroin
• One group of the experimentals received Heroin in A
• One group of the experimentals received Heroin in B
• The control group's test condition was receiving Heroin

Context Conditioning & Heroin

• DV: Mortality
• Same: 32.4%
• Different: 64.3 %
• Control: 96.4%
• This demonstrates that Context conditioning affects tolerance

Classical Conditioning in Clinical Settings

• With phobias caused by classical conditioning, classical conditioning techniques become useful to eliminate or reduce them
• Presenting the CS without the US extinguishes an unwanted CR
• Systematic desensitisation is a program of presenting the CS without the US, because phobias persist
• Phobias persist because people avoid situations where they see the phobic object avoid opportunities to extinguish the fear
• They can also be self-sustaining if someone is embarrassed to overcome a fear of crowds

Systematic Desensitisation

• Systematic desensitisation gradually exposes the client to the phobic object in a gradual way
• This is done by constructing a fear hierarchy
• Participants are given relaxation training
• Psychologists gradually expose the client to things higher on the fear hierarchy as they relax
• Systematic desensitisation lead to 60% continuing to fly after 3.5 years

Mind Blowing Learning Studies from Neuroscience

• Susumu Tonegawa found that you can implant false memories in the brains of mice
• This is done by Optogenetics: using light to control neurons that have been genetically modified to express light-sensitive ion channels.
• Researchers isolated cells that make up memory traces for a specific memory and reactivated it using a technology called optogenetics
• Mouse hippocampal cells were engineered to express the gene for channelrhodopsin, a protein that activates neurons when stimulated by light.
• The scientists also modified the gene so that channelrhodopsin would be produced whenever the c-fos gene, necessary for memory formation, was turned on

Optogenetics Results

• Researchers conditioned mice to fear a particular chamber
• During learning, the c-fos gene and channelrhodopsin gene was turned on, isolating memory trace cells with light-sensitive proteins.
• The next day, mice were put in a NEW chamber (no fear, never experienced before)
• A pulse of light to the hippocampus, stimulating the memory cells labeled with channelrhodopsin led to a fear response
• Results showed it is possible to elicit a specific memory by directly neurons that was active during learning
• A new study involved Mice in chamber A (no shocks, cells isolated/labelled) then the next day put them in chamber B where they received shocks
• During that time, memory of A via optogenetics was stimulated
• The next day, back in A, the mouse now showed a fear response, showing that you can create a false memory via stimulating neurons

Summation Test for Conditioned Inhibition

• Purpose: Tests whether a suspected inhibitory stimulus can suppress a conditioned response in a new context.
  1. Train Stimulus A to predict a response (e.g., a tone signals food, so the animal salivates).
  2. Train Stimulus B as a potential inhibitor (e.g., tone + light = no food). The animal learns that when light is present, food will not come.
  3. Now, introduce Stimulus B (light) into a new pairing (e.g., with a different excitatory stimulus).
  4. If Stimulus B reduces the response, this suggests true inhibition.
• Example A dog learns that a bell predicts food, so it salivates, and also learns that bell + light means no food, so it stops salivating when the light is present
• So, if the light is introduced with a different conditioned stimulus, and it still reduces salivation, it proves the light has inhibitory properties.
• The inhibitory stimulus suppresses behavior even when introduced to a new context

Retardation Test

• Tests whether a previously inhibitory stimulus is slower to become excitatory compared to a neutral stimulus
• Train Stimulus A to be an inhibitor (e.g., light signals no food), then try to condition Stimulus A as an excitatory stimulus (e.g., now making light predict food)
• If learning is slower than for a neutral stimulus, it confirms true inhibition.
• Example: If a dog learns that a light means no food, it should be harder to later teach it that the light now predicts food
• If the light was neutral to begin with, it would be conditioned to predict food much faster, meaning if learning is delayed, it means the stimulus had a real inhibitory effect before