learning chapter 3

8/14/2019 Learning Chapter 3

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Chapter 3

Pavlovian Conditioning


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Pavlovian Responses: Its not just aboutsalivation..

salivation, eye blinks, startle,nausea, tears-

but also.

pain attraction

anxiety arousal

fear happiness

disgust amusementsadness relaxed state

repulsion love (the kind you fall into)

anger

Classical conditioning applies to responses that we do not experience

as voluntary, purposeful, or under our willful control.

They involve passive responses---responses that happen to us, or that we undergo.

We salivate, but we dont do salivation like we do our chores.

A neurological view of Pavlovian responses has also been proposed---


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The Nervous System

Classical

Conditioning

Operant

Conditioning


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Autonomic Nervous System (ANS)

Sympathetic NSArouses

(fight-or-flight)

Parasympathetic NSCalms

(rest and digest)


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The basic form of classicalcond.

A new stimulus gets paired withanother stimulus that produces apredictable, automatic response (reflexor autonomic activity).

The new stimulus can then come toelicit the original automatic response.


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The basic form of classicalcond.

+

Loud thunder automatically causes startle/fear

After repeated pairing of lightning with thunder, lightning itself produces the response


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Fears/PhobiasBeing stuck with a needle causes pain/fear

Pain/Fear/Stress+

Fear/Stress

Now the sight of a syringe cause fear/stress


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Attraction

Arousal/Attraction+

Arousal/Attraction

Closeness/Caress produces attraction

Security blankets, fetishes, inappropriate attractions (pedophilia)
http://www.mysweetaromas.com/images/Ck%20Be%20Perfume%20by%20Calvin%20Klein%20for%20Women.jpghttp://www.mysweetaromas.com/images/Ck%20Be%20Perfume%20by%20Calvin%20Klein%20for%20Women.jpg


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Food/Taste Aversions

Nausea/Vomiting

Alcohol causes nausea, dizziness, vomiting

+

Sight, taste, smell

Sight, taste, smell

Revulsion/Disgust

Same with foods. The illness might

even be due to other conditions,

such as viruses, flu, etc


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Musical Responses

Fear

Fear

Theme from Jaws

Tubular Bells

+

+

HappyOur Song +


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Unpopular Mustache


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Ivan Pavlov (1849-1936)

Russian Physiologist

Specialty: Digestion

Nobel Prize, 1904, for his work

on the digestive system

b. Ryazan, Russia

Poor: Father a priest

Started as seminarian. Left to study physical sciences, U. St. Petersburg


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Pavlov in his lab with hisfavorite experimental subject


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Pavlovs accidental discovery

Wanted to measure quantity andcomposition of saliva in response tofood in mouth.

Problem: dogs began to salivate before

food was administered, to everyonesannoyance.

Salivated to sight of researchers, door opening,footsteps, bowl

Pavlov called this phenomenon PsychicSecretions

He realized he had discoveredsomething psychological, and, aftermuch debate, directed his research to


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Pavlovs Experiments

Before conditioning, food produces salivation.However, a tone (neutral stimulus) does not.


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Pavlovs Experiments

During conditioning, the neutral stimulus (tone)and the food are paired, resulting in salivation.After conditioning, the neutral stimulus (tone)

elicits salivation.


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Formal Definitions

An unconditioned stimulus (US) A stimulus that triggers an unconditioned

response.

Examples: food, loud noises, painful stimuli

An unconditioned response (UR) An unlearned response to an

unconditioned stimulus. Examples: salivation to food, jumping when

hearing a loud noise, moving away fromsomething painful


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Formal Definitions

A conditioned stimulus (CS) A neutral stimulus (an event) that comes

to evoke a classically conditioned

(learned) response due to beingpresented shortly before the US. In Pavlovs experiments, the CS was the tone.

A conditioned response (CR) A learned response to a classically

conditioned stimulus. In Pavlovs experiments, salivation to the bell was

the CR.


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Learning the 4 Key Terms

US

UR

CS

CR


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First, identify the existingreflex pairThis reflex pair is always the USUR

The rest is easy.


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Nice Notation.

US UR (identify the reflex pair)

CS : US UR (pair a neutral stim. with theUS)

CS CR (CS elicits response; nowcalled CR)

Food Salivation

Tone : Food Salivation Tone Salivation


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What use?

Based on our experiences, classicalcondition builds a set of signals orpredictive cues for potentially important

things to come. Builds an early warning system: even

warning us of good things to come.

We become physiologically prepared forwhat might be coming next.


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Factors that affectconditioning Pairing CS and US (4 ways)

Contiguity (closeness in time)

Contingency (predictive value of CS)

Stimulus Features

Overshadowing: Salience, intensity, Sensory preconditioning

Prior Experience Latent Inhibition

Blocking Number of Pairings

Intertrial Interval


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Contemporary human eyeblink preparation

Just relax

Puff Blink

Bell : Puff Blink

Bell Blink


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Pairing: Trace Conditioning

The CS begins and ends before the US is presented.


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Delayed Conditioning

The CS and US overlapi.e., the US is presented while the CS is still being presented


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Simultaneous Conditioning

The CS and US coincide exactly in time.


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Backward Conditioning

The CS comes after the US


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Which pairing procedure works best forcreating learning?

Given our notion that classicalconditioning establishes signals or cuesfor important future events, which

procedures might be best? Whichworst?

Think of the rattle snake.


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Which pairing works best?

All things being equal, delayed

conditioning is most effective.

Followed very closely by traceconditioning.

Simultaneous conditioning is weak. Backward conditioning is the weakest,

almost impossible.

Why are the last two so ineffective?

They do not signal what is coming up.

One of Pavlovs students found that when the smell of vanilla (CS) came

before the US (acid in the mouth), conditioning of salivation occurred in 20

trials. But when the smell came after the US, conditioning did not occur evenafter 427 pairings (after which he gave up).


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Another Factor: CS-USContiguity Contiguitycloseness in time between

two events.

In classical conditioning, CS-US

contiguity refers to the interval of timebetween the CS and US.

This time is called the InterstimulusInterval (ISI) Defined differently for trace and delayed

conditioning.


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CS-US Contiguity

Interstimulus Interval (ISI)

Interstimulus Interval (ISI)


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Delay ConditioningShort-Delay

US begins shortly (a second or less) after the CS begins.

Long-Delay

US begins several seconds or minutes after the CSbegins.


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CS-US Contiguity

In general, the shorter the ISI, thequicker the learning.

With simultaneous conditioning, in

which there is no interval at all, learningis very slow.

Rule of Thumb: Make the interval as

short as possible, just short ofsimultaneous presentations. NB: This rule of thumb has many

exceptions, depending on the species of

organism, the kind of response being


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Another Factor: Contingency Contingency is related to prediction

does one event, A, predict anotherevent, B If A, then B

In classical conditioning, it has to dowith the consistency of pairing CS andUS. If CS, then US (follows)

If the CS is always followed by US, youhave perfect contingency.

But what if the CS is followed by the US

inconsistently?


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Contingency: Rescorla (1968) Rats

Shock (US) Fear (UR)

CS = Tone

Three conditions CS presented without US 10% of time 20% of time

40% of time

Results:


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Contingency: Rescorla (1968)

Greater contingency,

More learning


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Stimulus Features

Almost any stimulus that can be detectedcan become a CS, but some are moreconditionable than others.

Compound Stimuli Studies of Pavlov

Two or more CSs presented at the same time justbefore the US is presented. [Tone & Light] : Food Salivation

Each CS then tested individually

Often, only one of the stumuli shows strongconditioning

Overshadowing if one CS is more intense orsalient, the other CS may be ignored Strong light better than weak tone

Loud tone better than weak light


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Sensory Preconditioning Sensory preconditioning is another

example of stimuli influenced bycompound events.

Sensory Preconditioning- two stimulisuch as light and tone are repeatedly

presented together without the occurrenceof a US (preconditioning).

Later, only one of these stimuli(e.g., tone) is paired with a US

(e.g., a shock).Then other stimulus (light) is

tested for conditioning.

Even though the second stimulus (light)

was never directly associated with the US


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Prior Experience with CS & US

Suppose you present a CS (e.g., a tone)repeatedly all by itself (never with a US likefood or shock).

You then start pairing the CS with a US,

trying to establish conditioning. How will the conditioning compare to

standard procedures (where the CS isnt atfirst repeatedly presented alone)?

In general, learning is slower. Latent Inhibition: The repeated appearance

of the CS without the US seems to inhibitthe ability of the CS to elicit the conditioned

response.


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Latent Inhibition: the more pre-exposures of the CS without the US,

the slower the learning.


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Why does latent inhibitionoccur? Remember contingency effects: learning is

stronger when the CS predicts the UCS (IfCS, then US) a greater proportion of thetime.

In latent inhibition, there is no contingencyduring the initial pre-exposure period.

Basically, since the CS seems unrelated tothe US for a while, it takes more contingent

presentations (CS

US) before theorganism believes there is really arelationship.

A completely new stimulus is a better CS

than an older stimulus that didnt seem to


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Prior Experience:Blocking in Compound Stimulus Studies

Leon Kamin discovered that sometimesa new CS cannot be establishedeffectively.

This occurs when the new CS is part ofa compound stimulus study with apreviously established CS.

A picture is worth a thousand words.

K i


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KaminBlocking

1. Light is established as a CS for eliciting

salivation.

2. Now the light and a new CS (tone)

are presented together before the US, andthe compound stimulus elicits salivation.

3. Now test the original CS (light): it still

elicits salivation.

4. Now try the tone by itself: conditioning

does not occur.

The tone was blocked by the previous

conditioning of the light


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Blocking Blocking resembles overshadowing, in

which one CS in a compound stimulus getsovershadowed by another stronger or moresalient CS.

In overshadowing, both stimuli (CSs) in the

compound are new stimuli. But in blocking, one of the CSs is previously

established and is known to elicit the CR.

In blocking, the new CS often doesnt addanything more to the established CS inpredicting the US.

If an employee can predict the stock market

with 100% accuracy, would you hire


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Number of Pairings

Acquisition (learning) curve

Non-linear

Asymptote

Conditioning Trials

CRS

trength

asymptote


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Intertrial Interval The intertrial interval (ITI) is the time

between each CS-US pairing (i.e., betweentrials).

Recall that the shorter the interstimulusinterval (ISI), i.e., when the CS is closer tothe US in time, the better the learning.

But what about the interval between trials(ITI)? Is learning stronger when the time

between trials is brief or longer? Counter-intuitively, more time between

trials often produces better learning.


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Other Variables AffectingConditioning

Age: Older people do not condition as readily

as younger people.

Stress: People and other organisms condition

more readily when under stress.

Note: Stress hormones consolidate memories.

(e.g., flashbulb memories)


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Learning, then losing it:Extinction Continued pairing of CS (tone) with US

(food) maintains the CR (salivation),i.e., the learning is maintained.

Repeated presentation of the CS

without US leads to a weakening andstopping of the CR: this is calledExtinction of the CR.

Pavlovs data: After repeated trials of showing dogs food then

giving it to them, the mere sight of food eventually elicitssalivation.

But when food was shown to dogs repeatedly without giving

the food to them, then, over time, the sight of food no longer

produced salivation---the response was extinguished.


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Spontaneous Recovery After extinction, let time pass

Present CS again by itself

Temporary, small return of CR

i i i


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Reacquisition

Establish a CSCR connection.

Extinguish CR by presenting CS alone.

Try to establish the CSCR connectionagain.

Conditioning the second time around is

much quicker. Fewer trials requiredthan the original learning prior toextinction.

ll h


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All Together Now.

Trials/Time

Strength

of

CR

Acquisition ExtinctionSpontaneousRecovery Reacquisition

CS&US CS alone CS alone CS&US

Hi h O d C di i i


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Higher Order Conditioning Association of CS and US is First-Order

Conditioning However, CSs can be associated with other,

established CSs

Second-order conditioning

salivation (CR)

first-order CS

tone (CS1) food (US)

second-order CS

Light (CS2)

Hi h O d C diti i


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Higher Order Conditioning Among humans, language is saturated with

higher order conditioning.

Staats & Staats (1957) Students observe non-sense syllables on a screen

(e.g., Laj, Qug, Yof, etc).

At the same time, Ss also repeat words spoken bythe experimenter. Sometimes repeated positive words (joy, peace,

love).

Sometimes repeated negative words (sad, thief,

foe) No natural US involved, just words

Students then rated nonsense syllables on a scalefrom pleasant to unpleasant.

Students rated the nonsense according to the

words with which they had been paired.Politics and Advertising

Th i f Cl i l


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Theories of ClassicalConditioning Substitution Theory (Pavlov)

The conditioned stimulus becomes a substitutefor the unconditioned stimulus

Learning depends only the number ofconditioned/unconditioned stimulus pairings


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Pavlov believed that conditioningdepended only on temporal contiguity:

(c)At the start of conditioning, activity in

the UCS center automatically causesactivation of the UCR center. At this timeactivity of the CS center does not affectthe UCS center.

(d)(b) After sufficient pairings of the CSand UCS, their simultaneous activitycauses the growth of a connectionbetween the CS and UCS centers.

Afterward, activity in the CS center willflow to the UCS center and thereforeexcite the UCR center.

Pavlovs Substitution Theory

P bl ith S b tit ti


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Problems with SubstitutionTheory If substitution of CS for US is what is

really happening, then UR should bevery similar to CR

A lot of time, this does happen, but not

always Sometimes, UR and CR look different

Also, stimulus substitution theoryassumes that simple contiguity(repeated pairing of CS and US)

establishes conditioning.

Sit ti h Sti l


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Situation where Stimulus-Substitution does not explain

events

Jump (UR) Freeze (CR)

Shock (US) Jump, freeze, +heart rate (UR)

Tone: Shock (US) Jump, freeze, +heart rate (UR)

Tone (CS) Freeze only, -heart rate (CR)If the CR differs from the UR,

simple substitution does not

seem to be the full story.

Rescorla Wagner Model: A


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Rescorla-Wagner Model: AMathematical Model of Classical

Conditioning Proposes that there is a limit to how muchlearning can occur through the pairing of aCS and US.

A CS acquires a limited amount of

associative strength on each trial (drawnfrom the limited pool available).

Associative strength amount of learning. Notation: V = associative strength

Maximum associative strength Notation: = Vmax = Upper limit of associative

strength (V)


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V and Vmax ()

Trials

0 2 4 6 8 10

AssociativeStrength

0

2

4

6

8

10

VMAX

Si=0.25

VMAX=10.00

VSUM= 0.00

J

=

V

Th R W ti f i l


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The R-W equation for a singleCS Vnn = c( Vn-1)

Vnn = amount of change in associative strength= amount of change in associative strengthon trial non trial n

Vn-1 = associative strength on the previous trial

= Vmax = maximum possible associativestrength

c = salience/intensity of the CS (varies from 0-1, with higher values meaning greater

salience/intensity).

Using this equation, we can plot V (associative

strength) acquired at each trial, which gives a

V i (i V )


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Varying (i.e., Vmax)

c = .50

= 100

c = .50

= 65

R W:Varying c (i e


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R-W:Varying c (i.e.,salience/intensity)

c = .10

= 100

c = .50

= 100

Higher salience, faster learning

Extinction of a CS


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Extinction of a CS

c = .30 = 100

US always follows CS

c=.30

= 100

Beginning with trial 10,

CS presented without US(like a bell without food)

R W and Contingency


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R-W and Contingency

c = .30

= 100US always follows CS

c = .30

= 100

US only sometimes follows CS

Note that learning is slower

never reaches = 100 over same

number of trials.

R W and compound stimuli


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R-W and compound stimuli

Competitive learning: The total learningavailable, , must be shared by eachstimulus in a compound. Thus, the amount

of learning to each stimulus is less in acompound than if that stimulus is alone.

R W and Compound Stimuli:


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R-W and Compound Stimuli:OvershadowingTwo stimuli, a tone (CS1) and a light (CS2), presented simultaneously over all trials.

c 1= .25

c 2 =.25

= 100

same salience

c 1= .25

c 2 =.10 = 100

The more salient stimulus overshadows the other.

R W and Blocking


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R-W and Blockingc 1= .25

c 2 =.25

= 100

same salience;

Both CSs present on all trials

c 1= .25

c 2 =.25

= 100

same salience;

CS1 by itself for six trials

Then both CS present thereafter

So, when one CS established first,

it blocks the second from becoming

established

Rescorla Wagner


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Rescorla-Wagner Good mathematical model, accounting

for Nonlinear learning curves with upper limit

Salience/intensity of CS

Extinction

Contingency

Overshadowing

Blocking

But, doesnt account for CS-US contiguity (time between CS and US)

Latent Inhibition

Spontaneous Recovery

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