Chapter 8 - Extinction and Stimulus Control

Extinction

Nonreinforcement of a previously reinforced response, the result of which is a decrease in the future strength of that response

-Ensure that it is the removal of the reinforcer

Side Effects of Extinction

1. Extinction Burst - Temporary increase in the frequency and intensity of responding when extinction is first implemented

2. Increase in Variability - Ex; rat that pressed level with left paw may try with its right paw

3. Emotional Behaviour - Changes like agitation and frustration

4. Aggression - Frustration-induced aggression common in humans as a result of a goal being blocked

5. Resurgence - reappearance during extinction of other behaviours that had previously been effective in obtaining reinforcement

• Resembles “regression” - reappearance of immature behaviour in reaction to frustration or conflict

6. Depression - Shown in low activity

-Side effects can inadvertently be strengthened if one suddenly provides the subject with the reinforcer

Resistance to Extinction

Extent to which responding persists after an extinction procedure has been implemented, effected by:

1. Partial reinforcement effect

2. History of reinforcement

3. Magnitude of the reinforcer

4. Degree of Deprivation

5. Previous experience with extinction

6. distinctive signal for extinction

Partial Reinforcement Effect

Process whereby behaviour that has been maintained on an intermittent (partial) schedule of reinforcement extinguishes more slowly than behaviour maintained on a continuous schedule

-Resistance is particularly strong when maintained on a variable interval or variable ratio schedule

-Helps account for types of maladaptive behaviours that are hard to eliminate

History of Reinforcement

The more reinforcers that an individual received for a behaviour, the greater the resistance to extinction

-Resistance to extinction reached its maximum after 1,000 reinforcers

Magnitude of the Reinforcer

Large magnitude reinforcers result in greater resistance than small magnitude reinforcers

-Effect is not always consistent; small reinforcers can also result in greater resistance

Degree of Deprivation

The greater the level of deprivation, the greater the resistance to extinction

Previous Experience with Extinction

The greater the number of exposures to extinction, the quicker the behaviour will extinguish during subsequent exposures

-Ex; rat experiences several sessions of extinction interspersed with reinforcement; it will learn to stop lever pressing once an extinction procedure begins

Distinctive Signal for Extinction

Occurs more quickly when there is a distinctive stimulus that signals the onset of extinction

Spontaneous Recovery

Reappearance of an extinguished operant response, despite continued absence of reinforcement following a rest period after extinction

-Each recovery is weaker and more readily extinguished

-Skinner proposed it may be a function of a distinctive stimulus associated with the start of a session

Differential Reinforcement of Other Behaviour

Reinforcement of any behaviour other than a target behaviour that is being extinguished

-More effective than simple extinction because target behaviour wakened by:

1. Lack of reinforcement for that behaviour

2. Reinforcement of alternative behaviours that come to replace it

Functional Communication Training - Type of differential reinforcement procedure, behaviour of clearly and appropriately communicating one’s desires is differentially reinforced

Can reduce unwanted side effects of extinction (aggression and frustraiton)

-To extinguish one behaviour, must provide plenty of reinforcement for appropriate behaviour

Stimulus Control

Situation in which the presence of a discriminative stimulus reliabily affects the probability of a behaviour

Ex; if a 2000HZ tone signals a lever pressing will lead to food

2000HZ tone (sD); Lever press (R) → Food (sR)

-The rat only presses the lever in the presence of a tone, the behaviour of lever pressing is said to be under stimulus control

Real Life Examples: Stopping at a red light, going when green, saying “thank you” and “you’re welcome” based on certain responses

Stimulus Generalization

Tendency for an operant response to be emitted in the presence of a stimulus that is similar to a distinctive stimulus

-Generalization Gradient - Measure of the strength of responding in the presence of stimuli that are similar to the sD (or CS) and vary along a continuum

Steep Gradient = Rate of responding drops sharply as stimuli become increasingly different from sD

Flat Gradient = Responding drops gradually as stimuli become increasingly different from the sD

Steep = Less generalization, Flat = more generalization

Stimulus Discrimination

Tendency for an operant response to be emitted more in the presence of one stimulus than another

-Steep gradient = more discrimination, flat gradient = less discrimination

Discrimination Training

Reinforcement of responding in the presence of one stimulus (the sD) and not another stimulus

Ex; 2000 Hz Tone (sD); Lever press (R) → Food (sR)

— 1200Hz Tone (sT); Lever press (R) → No food (-)

-After repeated exposure, rat will learn to press the lever in the presence of only the 2000Hz tone and not in the presence of the 1200 HZ tone

-Responses that occur in the presence of sT are not reinforced (Distincriminative stimulus for extinction)

Peak Shift Effect

Following discrimination training, the peak of a generalization gradient will shift from sD to a stimulus that is further removed from the sT

Ex; train rat to press lever at 2000Hz presence, then conduct test for generalization between 1200-2800Hz

-Submit rat to discrimination training procedure (lever reinforced at 2000 Hz, sD) not at 1200Hz tone (sT) then test again for generalization

Difference: Discrimination training has gradient drop off more sharply on the side toward the sT, rat strongly discriminates between the sT and sD

-But after discrimination training strongest response shifts away from the sD to a stimulus in a direct opposite to the sT, this shift in generalization gradient peak is the peak shift effect

Explanations for the Peak Shift Effect

1. During discrimination training, subjects response in terms of the relative, not absolute values, of the stimuli

• So the rat learns that a 2000Hz tone doesn’t just indicate food, rather it learns that a higher pitched tone indicates food and a lower-pitched tone indicates no food, so the rat emits a stronger response to a tone with a higher pitch than the sD

2. Despite discrimination training, sD is still somewhat similar to the sT and has acquired some of its negative properties

• 2000Hz tone sD is similar to the 1200Hz tone (sT) making the 2000Hz tone less attractive than it would have been if the sT had been trained. Thus, a tone that has a slightly higher pitch than 2000Hz, and is thereby less similar to the 1200Hz, tone will result in the highest rate of responding