Chapter 6

transcript

Chapter 6

Learning and Behavior

Learning

A more or less permanent change in behavior that results from experience

Behavior

The ways in which animals act or respond in an environment– influenced by both biological and learned

components

Richard Dawkins: Memes

A cultural invention that is passed on from one generation to the next

Marvin Harris (1974)– “Our primary mode of biological adaptation

is cultural not anatomical”

Ivan Pavlov

Learning is an associative process– Pavlov studied a learned association

between a neutral stimulus and a reflexive response

Classical Conditioning

US - Unconditioned Stimulus– stimulus that evokes the behavioral response of

interest (Meat powder) UR - Unconditioned Response

– the reflexive response to the presentation of the US (Salivation)

NS - Neutral Stimulus– a stimulus that does not result in an

unconditioned response (Bell)

NS (Bell)No UR (No Salivation)

Before Conditioning

produces

Before Conditioning

NS (Bell)No UR (No Salivation)produces

produces

US (Meat) UR (Salivation)produces

produces

NS (Bell)+

US (Meat) UR (Salivation)

During Conditioning

produces

Trial 1

NS (Bell)+

During Conditioning

produces

Trial 2

NS (Bell)+

During Conditioning

produces

Trial 3

NS (Bell)+

During Conditioning

produces

Trial 4

CS (Bell) CR (Salivation)

After Conditioning

produces

CS - Conditioned Stimulus (Bell)– what used to be called the neutral stimulus.

• Initially it evoked no response, but, after conditioning, it now evokes a response

CR - Conditioned Response (Salivation)– similar (but often not identical to) the

unconditioned response• but is evoked by the conditioned stimulus

Habituation and Sensitization

Can animals learn without association? Habituation

– Decreased responsiveness to repeated stimulation

Sensitization– Increased responsiveness following a

single stimulus presentation

Extinction

A reduction in the conditioned response when the conditioned stimulus is presented without the unconditioned stimulus– e.g. presenting the bell repeatedly without

the meat will eventually eliminate the salivation

Spontaneous Recovery

The reappearance of the conditioned responses following a delay in the extinction process

Trials

AcquisitionBell+Meat

ExtinctionBell Only

SpontaneousRecoveryBell Only

Higher Order Conditioning

First Order Conditioning:– Associating Bell + Meat Powder eventually

leads to salivation to Bell alone (Bell = CS1)

Higher Order Conditioning– Associate CS1 with a new CS (e.g. Light)

– Associating Bell + Light eventually leads to salivation to Light alone (Light = CS2)

CS1 (Bell)+

NS (Light) CR (Salivation)

During Conditioning

produces

CS2 (Light) CR (Salivation)

After Conditioning

produces

Important:The Light is never directly

associated with meat

Basic Rules of Conditioning

The more association trials, the better the conditioning

CS and US must be closely linked in time

Physically intense stimuli are conditioned more easily

Some things are more easily conditioned than others

Stimulus Generalizationand Discrimination Stimulus Generalization

– Animals will show a Conditioned Response to stimuli similar to the original CS

Stimulus Generalizationand Discrimination Discrimination

– If you repeatedly associate one CS with the US and do not associate the second, the CR will discriminate the two

CS+ CS-

Figure 6.4

Real-Life Examplesof Classical Conditioning Conditioning Emotional Responses

– Baby Albert (Watson and Rayner, 1920)• Conditioned fear to a white rat by

associating a loud noise with the rat– CS = rat– US = loud noise– UR = startle to loud noise– CR = startle to rat

Real-Life Examplesof Classical Conditioning Learning the meaning of words

– Word is associated with the sensory impression

• e.g. “apple” and view of an apple

– “Second-signal system”

Real-Life Examplesof Classical Conditioning Conditioned Taste Aversion

– a taste (CS) associated with a toxin (US) leads to nausea (UR)

– later, the taste alone evokes nausea (CR)

Real-Life Examplesof Classical Conditioning Drug Tolerance

– drug users become increasingly less responsive to the effects of the drug

– tolerance is specific to specific environments (e.g. bedroom)

– familiar environment becomes associated with a compensatory response

• taking drug in unfamiliar environment leads to lack of tolerance

Instrumental Learning

Pavlov– Classical conditioning of reflexes

Can learning occur with nonreflexive behavior?– Instrumental Response: a voluntary

response that acts on the environment in a meaningful way

Instrumental Learning

The modification of instrumental responses using reinforcers and punishers

E.L. Thorndike’s Puzzle Box

Cat placed in a box that can be opened from inside by pushing on latch

Initially, cat shows random behaviors– scratching– sniffing

Eventually cat will hit latch– hitting latch leads to pleasant

consequence - escape• increases likelihood action will occur again

Thorndike’s Law of Effect

Responses followed by “satisfiers” tend to be repeated

Those followed by “annoyers” are not repeated– useful behaviors are stamped in

Operants

B.F. Skinner:– An operant is an instrumental response

that operates on the environment Positive Reinforcer

– Any stimulus that increases the likelihood of an operant response

Skinner developed a general model of learning called “operant conditioning”

The Operant Chamber

Shaping Behavior

Reinforce responses that approximate the target behavior

Secondary Reinforcement

Neutral stimuli can acquire reinforcing properties through the process of higher-order conditioning– e.g. the reinforcing effect of language

(“good boy”)

Schedules of Reinforcement

Rate at which reinforcer is delivered influences nature of response

Continuous reinforcer– each response is reinforced

Partial Reinforcement– reinforcer is not delivered for each

response

Partial Reinforcement

Fixed Ratio (FR) Schedule– reinforcer is delivered only after a fixed

number of responses have been made• e.g. FR-10 schedule: reinforcer

delivered after every 10th lever press

Variable Ratio (VR) Schedule– the number of responses before a

reinforcer is delivered varies

Fixed Interval (FI) Schedule– the first response following a specified time

interval is reinforced• e.g. FI-10 schedule: only responses

made after 10 seconds are reinforced

Variable Interval (VI) Schedule– the first response following a varying time

interval is reinforced

Partial Reinforcement affects Response Rate

Partial Reinforcement Effect

If you train an animal using partial reinforcement, it is more resistant to extinction than one that received continuous reinforcement

Extinction– a reduction in the rate of response when a

reinforcer is withheld

Differential Reinforcement

Differential Reinforcement of a High Rate of Response (DRH)

– reinforce bursts of responses

Differential Reinforcement of a Low Rate of Response (DRL)

– reinforce pauses between responses

Behavioral Control

Skinner:

– The likelihood of any behavior depends on reinforcement and punishment contingencies

Environmental Determinism

– environmental stimuli exert total control over behavior

Stimulus Control

The Discriminative Stimulus (Sd)– a signal that indicates when a response will

be reinforced• e.g. reinforcing lever pressing only when light is

Negative Discriminative Stimulus (S)– A signal that indicates that a response will

not be followed by reinforcement

Stimulus Control

Responding only in the presence of Sd

and not in the presence of S

Punishment

Another potential consequence of behavior– An aversive stimulus that decrease the rate

of responding When is punishment most effective?

– It must be relatively intense– It must follow the response relative quickly– It must be applied consistently

Negative Reinforcement

Any stimulus whose withdrawal increases the probability of a behavior– e.g. pushing a lever to turn off a shock

Avoidance Learning– when an instrumental response prevents

and aversive stimulus• e.g. pushing a lever before the onset of shock

Persistence of Avoidance Learning Negatively reinforced responses show

slower extinction than positively reinforced responses– avoidance learning - gaining both positive

reinforcement and avoiding punishment

Observational Learning

Not all learning occurs through direct reinforcement

We can learn by watching others and through imitation

Limitations to Pavlov’s andSkinner’s Theories of Learning Instinctive Drift

– Animals will often show instinctive behaviors even if they are not being reinforced

• e.g. raccoons “washing” coins

Limitations to Pavlov’s andSkinner’s Theories of Learning Cognitive Maps

– Animals can create a mental representation of a maze even if they haven’t been reinforced to solve the maze

Limitations to Pavlov’s andSkinner’s Theories of Learning

Latent learning– when animals that

have not been reinforced are reinforced, they show faster than expected learning

Limitations to Pavlov’s andSkinner’s Theories of Learning Preparedness

– some associations are learned more easily than others

• e.g. associating taste with nausea is easier than associating noise with nausea

Conceptual Learning

Do associations or reinforcement explain all types of learning?

Learning to learn: – some animals can learn strategies– win-stay, lose-shift: continue response if

reinforced, switch response if not reinforece

Behavioral Complexity and Environmental Complexity The more complex the behavior, the

more complex the environment required

Chapter 6

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