version 0.1 (c) celest 20071 associative learning

Version 0.1 (c) CELEST 2007

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Associative Learning


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Challenge Questions• You are a psychologist treating a patient who is

addicted to smoking. Explain how you would treat the patient’s addiction.

• You are a therapist who has a patient with a fear of spiders. Their spouse loves the outdoors and this fear interfering with their marriage. How would you treat this patient?

• You are a coach of a football team and your quarterback is throwing too many incomplete passes. Explain how you would use learning theory to help his game.


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The Smoker’s Brain

• The smoker would care.• Nicotine influences the

levels of certain neurotransmitters.

• Nicotine can prevent the break down of dopamine, increasing its presence in brain neurons.

• This causes the pleasurable effects of smoking.


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The Phobic’s Brain

• The amygdala is activated by a relatively harmless stimulus.

• This creates a fear response.

• In a patient with a phobia inhibition by the prefrontal cortex does not occur.


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The Quarterback’s Brain

• The cerebellum coordinates and controls movement.

• Despite its small volume, it contains nearly half the cells in the entire brain.

• Cerebellar damage impairs the timing of one’s movements.


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Outside of the Black Box

• Learning is something that can be observed without observing the brain directly.

• In fact, behavioral psychologists treat the nervous system as a “black box” and focus mainly on relationships among observable stimuli and behaviors.


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ASSOCIATIVE LEARNING

Classical conditioning: learning associations between objects.

learning associations between objects.

Operant conditioning: learning that, in a particular situation, a certain response leads to a certain outcome.

There are two types of associative learning:


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Classical Conditioning


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Ivan Pavlov

• Classical Conditioning was discovered by the work of Ivan Pavlov.

• He was studying digestive physiology for which he won the Noble Prize.


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CLASSICAL CONDITIONINGAn object or an event that you sense is referred to as a stimulus

We distinguish two types of stimuli and responses:

• Unconditioned stimulus (US) A stimulus that naturally evokes a response or reflex called the Unconditioned Response (UR)

• Conditioned stimulus (CS) A stimulus that does not naturally evoke a response. However, it can acquire the ability to elicit the response, called the Conditioned Response (CR).


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PAVLOV’S EXPERIMENT


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Stimulus Generalization

• Stimulus Generalization occurs when animals respond more to stimuli that are similar to the original than to those which are different.

Example: The dog in Pavlov’s experiment would also salivate to tones of similar frequencies to the original.


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Stimulus Generalization Gone Wrong!• In 1920, little Albert, an eleventh month old orphan,

learned to fear a rabbit.

• Eventually all white fuzzy objects caused the same fear in little Albert even though they were not paired with the US (loud sound).

and

But if you present simultaneously

many times, then

Initially, the soundcauses fear…

But not the rabbit

… the rabbit also causes fear!


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Stimulus Discrimination

• Stimulus Discrimination occurs when animals are conditioned to respond to one specific CS and not others.

Example: Only a tone of a specific frequency is followed by food. Other tone frequencies are presented without food. As a result, the dog only salivates after the tone of a specific frequency.


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The Sequence of Events

• Acquisition: the gradual increase in the strength of a response that occurs with the pairing of a CS with a US.

• Extinction: occurs when the CS is presented without the US causing a decrease in the strength of the response.


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Classical or Pavlovian Conditioning

Strengthof CR

Time/Trials

Acquisition(CS+UCS)

Extinction(CS alone)

Extinction(CS alone)

Spontaneousrecovery ofCR

Graph from Myers 6th Ed.


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Operant Conditioning


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OPERANT CONDITIONING

The frequency of a behavior is influenced by the presence or absence of a rewarding or aversive event after the expression of this behavior

This theory is called Behaviorism

B.F. Skinner developed the Skinner box to study this type of learning in pigeons. The pigeons learned to press levers to receive a reward!


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Sequence of Events

• Acquisition: The animal’s response produces a reinforcer.

Example: A rat presses a bar that produces food. The rat will begin to press the bar more frequently.

• Extinction: The animal’s response no longer produces a reinforcer.

Example: A rat presses a bar but it no longer produces food. The rat will press the bar less frequently.


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Schedules of Reinforcement


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Examples of SchedulesFixed Ratio Schedule: A rat is given food for pressing a lever every 3 times.

Fixed Interval Schedule: A rat is given food for pressing a lever after 1 minute has elapsed.

Variable Ratio Schedule: A rat is given food for pressing a lever an average of 3 times.

Variable Interval Schedule: A rat is given food for pressing a lever after an average of


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Associative LearningADAPTIVE TIMING:

ADVANCED MODELINGCLASSROOM PRESENTATION


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WHAT NEEDS TO BE MODELED?

Anatomy Neurophysiology

A Complete Circuit!


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EXPERIMENTAL PROTOCOL

US: air puff

Learning phase: for a selected number of trials, the sound is presented before the air puff (in delay or trace

conditioning)

Testing phase: the sound alone is presented to test for CR

CS: sound

UR, CR: nictitating membrane extension


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TIMING IS EVERYTHING!

The eye blink is a very transient response: must be made just prior to the air puff.

If it is done too late, the eye is not protected when the air puff occurs.

If it is done too early, the eye is not protected either since the blink ends too early!


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EXPLAINING ADAPTIVE TIMING

How does the brain learn to execute the right response at the right time?

We need to consider the neural circuits involved in producing the eye blink response

The critical structure is the cerebellum


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THE BIG ISSUES

The brain must have a way to keep track of time. It must have some kind of internal clock

Learning may take place over many trials: learning occurs at a certain rate which can vary

Both aspects can be studied through mathematical models


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INTERNAL CLOCK IN THE CEREBELLUM

Through a complex chemical process, some cells in the cerebellum can represent how much time has elapsed since a conditioned stimulus (CS) was presented

The same cells can also learn to associate the unconditioned stimulus (US) with the CS

Thus, these cells learn to time conditioned responses (CR)


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ANATOMY OF A NEURON


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CEREBELLAR CIRCUIT

The circuitry involved in adaptive timing involves a several types of cells connected in very specific circuits

The diagram illustrates that different circuits or pathways support specific sensory input (US, CS) and motor output (CR)


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US PATHWAY

The US signal due to the air puff to the eye travels in the pathway outlined in red

First it is relayed to the inferior olivary cell

Then it is communicated the Purkinje cell through climbing fibers


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CS PATHWAY

The CS signal due to the tone travels in the pathway outlined in green

First it is relayed to the pontine nuclei

Then it is sent to granule cells through mossy fibers

Finally, it reaches Purkinje cells via parallel fibers


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CR PATHWAY

Purkinje cells influence cells in the interpositus nuclei, which directly control the expression of the CR through a series of projections ending at the facial nucleus

The facial nucleus emits the appropriate motor response to cause the blink


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The Central Circuitry Involved in Adaptive Timing


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Required Parameters for the Cerebellar Model of Adaptive Timing of Eye Blinks


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A NEURAL NETWORK MODEL OF ADAPTIVE TIMING: INQUIRY THROUGH SOFTWARE 1

Model 1: Simple user interface for virtual experiments (for less experienced students)


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Model 1: Simple user interface for virtual experiments (for less experienced students)


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Model 2: More complex interface for more experienced users


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Model 3: Most functionality for most experienced users

version 0.1 (c) celest 20071 associative learning

Documents

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fear response

certain response

harmless stimulus

unconditioned stimulus

learning associations

conditioned response

types of associative