The Early Years • 19thÎ20th century: all about the atom

Theories of Learning Wouldn’t it be ironic if I did a poor job teaching this lecture?

– Atoms associated to become molecules

• Ebbinghaus: paired nonsense syllables • William James speculated that Associationism associations in the world reflected in brain • Belief in a brain-mind correlation •Configurationism Learning = forming associations

The Early Years

The Early Years

• Competing view at the time • The mind/brain is an integrated system • Brain functioning – Specialized brain areas – Operate in concert (principle of “mass action”)

Associationism

Associationism

Configurationism

Configurationism

Before WWII: Gestalt • Koehler was one of the associationists • Recall his experiments with the chimpanzees on Tenerife – Learning to use tools wasn’t done by chaining Behaviourism S-R sequences – Involved seeing the problem as a whole

• We all know what the fate of Gestalt was Gestalt • I’ll mention Koehler again later

Before WWII: Behaviourism • Behaviourists did away with vague terms like association and replaced them with terms like S-R and Conditioned Reflex • Watson: All learning is S-R Behaviourism • The dominant theme for the 1st half of the 20th century Gestalt

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Behaviourism: Clark Hull

Behaviourism: Clark Hull

• An attempt to extend behaviourist S-R paradigms to predict complex behaviour • Conditioning explains the mechanism of all learning • Wanted to learn what promotes learning S-R connections in the first place

• Drives (borrowed from Freud’s instincts) • Drives

– A rat won’t learn the maze if it’s never hungry

Behaviourism: Clark Hull

– Internal (hunger) – External (peer pressure)

• Reinforcement – reduces drive – Primary (food) – Secondary (money)

Behaviourism: Clark Hull • In the spirit of positivism, Hull proposed a mathematical model (easily testable) of behaviour

Response Threshold

– Hypothetico-Deductive Model

• Predict conditional probability of performing a behaviour: SER (reaction potential) • An example: P(BBQ some sausages)

Behaviourism: Clark Hull • What factors will influence SER? – Experience with BBQ food at reducing hunger? (SHR) – How hungry are you? (D) – How salient is the hunger? (V) – How much food are we talking here? (K) – Are we just tired? (IR) – Does our roommate usually give in and cook dinner? (SIR)

Behaviourism: Clark Hull • Let’s plug in some numbers to see a prediction: – Age 20: 17 summers of BBQ food (6 BBQs per summer), assume 50% satisfaction rate •

SHR

= 1 – 11-.03(17 x 6 x .50) = 0.97

– You’ve been to the gym: • About 80% as hungry as you’ve ever been (D=.8) • Your hunger is pretty salient (V = 1.0) • You’re really tired (IR = .27)

– Your moocher roommate does 1/3 of the cooking • Only 2 hotdogs left in the house (K=.8) • (SIR = .33)

.97 x 0.8 x 1.0 x .8 – 0.27 - .33 = .02

• Note that this formulation is probabalistic

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Behaviourism: Spence

Behaviourism: Spence

• Recall from Hull’s theory: – SER (energy available to respond to stimulus) depends on both positive (excitation) and negative (inhibitory) values

• Gestalt phenomena had been difficult to explain using S→R paradigm • Spence showed how learned associations (habit strength, SHR) can explain these phenomena

Behaviourism: Spence S Training

Critical Test

M

• Train an animal to respond to a square of a certain size (16 x 16 cm) versus a smaller square (12.6 x 12.6 cm) • Over 100 trials: – Strong habit strength for larger square • SHR= 1 – 11-.03(100)= .999

– Strong inhibition for the smaller square

• What about the Gestalt problem?

Behaviourism Summary

S

M

L

1

.64

.08

1

.64

L

1

• Inhibition and habit strength generalize to similar objects as a function of similarity – Training: S is most similar to S, M most similar to M – Critical test: inhibition from S transfers to most similar object (M), habit strength for M applies to M, but also applies to similar object (L)

• These two behaviourists worked to expand the range of behaviours that their paradigm could explain • Make specific predictions using operationally defined inhibition and excitation

• Response to Gestalt objections to behaviourism

But then a funny thing happened… • A realization that there was one important behaviour that behaviourism couldn’t explain – Koehler argued (correctly) that association learning insufficient to account for language

• Even Pavlov came to see this as a problem – Second Signal System – stimuli were not raw physical inputs (phonemes, lexemes) but language embedded in verbal codes – A sort of linguistic configurationalism

Zombie Gestalt strikes again • Gestalt sensibilities continued to have an influence • Earliest behavioural experiments were ideally devoid of context – Ebbinghaus’ nonsense syllables

• One Gestalt legacy was to force experimenters to account for context – Hull acknowledged role of organism’s goals

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Tolman

Tolman

• Behaviourism methods get a dose of context • Hull’s reinforcement driven S→R view contrasts with Tolman’s S→S view – Uses Gestalt principles to argue animals learn S-S connections without explicit biologically significant event to make learning occur

Tolman

– Knowledge of food locations not reinforced

• Hungry rats correctly navigated directly to food locations – If reinforcement required for learning, how did they learn the location when they aren’t hungry?

The Cognitive Revolution Cognitivism

You are here

– Learning is organizing things by their utility for achieving goals – trial and error is a looking back and forth to get the lay of the land in order to construct a solution – our cognitive maps are a record of goals and relevant paths

Tolman

• Learning without reinforcement • Satiated rats explored a maze

Behaviourism

• Cognitive maps • Learning is like mapmaking

• Cognitive maps contain expectancies made up of sign gestalts – Following landmarks – Changing landmarks disrupts navigation – Stores relative locations of objects/stimuli – Chain of associations – S→R alternative: learn associations between landmarks (S→S)

The Cognitive Revolution • Behaviourism’s failings most evident in problem of language acquisition • Had other failings too • S-R learning theory had nothing else to offer • Not a complete account of learning • By late 60s learning was being translated into the concepts of information processing • You’ll cover this at end of term

Gestalt

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Connectionism – Hebbian Learning

Connectionism – Hebbian Learning

Connectionism 1990

You are here

• We talked about Hebb yesterday, so I went back and deleted this slide. • 45 second savings

Hebbian Learning • Based on correlational learning (James, 1890) – When two events co-occur or follow in succession, the connections between the neural representations of these events will be strengthened

• “Cells that fire together wire together” – Excitatory (+): 2 events occur together – Inhibitory (-): 2 events are mutually exclusive

Hebbian Learning • Phase sequences – Individual neurons participate in multiple cell assemblies • red associated with {cherries, fire hydrants, …} • Lets you minimize # neurons – Context constrains phase sequences to relevant associations

Hebbian Learning • Cell Assemblies – Interconnected cluster of neurons – The physiological mechanism for learning – Learning occurs at synapses between neurons • Information is not in the neurons themselves • Grandmother cell

– Strengthening of connections • additional connections or growth

Hebbian Learning • Reverberation – Cell assemblies may have reentrant connections – Facilitates single-trial learning • Associations a function of frequency

– Consolidation mechanism – Pattern completion – Mechanism for working memory • Computer memory works similarly

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Hebbian Learning

From Hebb to Mastercard

A Simple Cell Assembly Demonstrating Reverberation

Hebbian learning at work • • • • • • • •

London, ON – Starbucks – 3.99 London, ON – Starbucks – 4.79 Cupertino, CA – Apple – 0.99 Cupertino, CA – Apple – 0.99 Cupertino, CA – Apple – 0.99 London, ON – Starbucks – 3.99 Cupertino, CA – Starbucks – 2.99 London, ON – Starbucks – 3.99

Mar 1 Mar 2 Mar 2 Mar 3 Mar 7 Mar 7 Mar 8 Mar 8

• Hebbian learning was first described almost 60 years ago • Mathematical modeling and computers incorporated these ideas into connectionism • connectionist networks can do simple human-like learning • Using Hebbian learning to detect credit card fraud: Priceless

Hebbian learning at work London

Cupertino Valid? Apple

Starbucks

Hebbian learning at work

Hebbian learning at work

London

London

Cupertino

Cupertino Valid? Valid

Valid? Valid

Apple

Apple

Starbucks

Starbucks

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Hebbian learning at work

Constructivism

You are here

London

Cupertino Invalid Valid? Apple Constructivism 1990 Starbucks

Important Figures • John Dewey (1859 – 1952) – Philosopher @ Columbia University – Epistemologist – Philosophical founder of constructivism

• Piaget – Cognitive constructivist

• Vygotsky – Social constructivist

• Piaget & Vygotsky appear in later lectures

Constructivism • Constructivism: knowledge is a constructed entity made through the learning process • Knowledge can thus not be transmitted from one person to the other – it must be reconstructed by each person

• Knowledge is relativistic – It varies over time; it is something to be built up

Constructivism • Behaviorism: knowledge comprises passive, automatic responses to stimuli • Cognitivism: knowledge comprises abstract symbolic representations in the head of individuals – Computer metaphor (e.g., binary code)

• Both of these views see knowledge as an absolute entity – You either know something, or you don’t

Constructivism • People learn by leveraging existing knowledge • Thus, learning will depend on what else is already known – Best method for teaching will attempt to capitalize on existing knowledge – The reverse of the behaviourist approach – Echoes Gestalt ideas

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The take home message Cognitivism

Associationism

Configurationism

Behaviourism

Gestalt

Connectionism

Constructivism

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