1. Operant Conditioning – Chapter 8
Theories of Learning
October 14, 2005
Class #23

2. Discriminative Stimulus (SD )
A stimulus in the presence of which responses are reinforced and in the absence of which they are not reinforced…
Basically, its a signal that a response will be followed by a reinforcer
It signals the availability of the reinforcer thus increasing the probability it will occur
The behavior then is considered to be under stimulus control
See next slide…

3. Stimulus Control
Having stimulus control means that the probability of the behavior varies depending upon the stimuli present
Our behavior often comes under stimulus control without our awareness
A person that contributes to charity generously while in church, but watches every penny spent while at work
SD  R  SR
??  ??  ??

4. Stimulus Control: Generalization
Generalization is when responses to one stimulus occur to other, usually similar stimuli
Generally, as the training and test stimuli become more different responding will decline, producing what is called a generalization gradient

5. Generalization Gradient
Guttman & Kalish (1956)
Pigeons were reinforced for pecking a 580 nm lit key (orange-yellow) on a VI schedule
A test session was then given where many different colored key lights were presented in extinction

6. Stimulus Generalization as a Measure of Stimulus Control
Training S+
Pigeons were trained to peck in the presence of a colored light of 580 nm wavelength and then tested in the presence of other colors.
Guttman & Kalish (1956)

7. Stimulus Generalization: Applied
Rincover & Koegel (1975) were attempting to train autistic children to imitate
One child, Joey, learned to touch his head when the Experimenter said “do this” and touched his own head; unfortunately, it took 300 trials
A generalization test in a different location and with a different experimenter, resulted in 0% correct responses
It turned out that the first Experimenter had frequently held Joey’s hands in his lap before each trial began
Another generalization test was conducted and this time the new experimenter held Joey’s hands first, then said “do this” & touched his head: resulted in 60% correct responding
A third test was conducted and the experimenter just held Joey’s hands in his lap: 100% correct responding
What gained stimulus control???

8. Stimulus Control: Discrimination
A better procedure for training Joey would have been to use discrimination training…
Discrimination training involves presenting at least 2 stimuli but reinforcing only one of them
Discrimination is differential responding to multiple stimuli
A discriminative stimulus for extinction (S∆) is a stimulus that signals the absence of reinforcement

9. Stimulus Control: Discrimination
Azrin & Hayes (1984) used discrimination training to increase males’ sensitivity to cues signaling females’ level of interest in males
Subjects were shown 24 film clips of couples conversing; half were positive instances of female interest and half were negative instances
Subjects were reinforced for correctly identifying whether each slide involved female interest or not
The male subjects increased their correct responses by over 50% as a result of the training

10. Stimulus Control: The Peak Shift Effect
The peak shift effect is when the peak of a generalization gradient shifts away from the S∆ following discrimination training

11. Hanson (1959)
Procedure
Several groups of pigeons pecking different colored key lights
The control group was trained with just one stimulus, a 550 nm key light, reinforced on a VI schedule
The experimental groups were given successive discrimination training with 2 key lights, the 550 nm light was always the SD, and different groups had a different wavelength as the S∆

12. Hanson (1959): The experimental group had a 590 S∆

13. “Mr. Shallow” example…
“Mr. Shallow” identifies women on just one quality – introversion vs. extroversion
He has just broken up with Jackie who is an introvert (he said she’s boring)
Jackie is the discriminative stimulus for extinction (S∆) here
Earlier in his life, “Mr. Shallow” had an exciting relationship with Liz who was a pure extrovert
Liz is the Discriminative Stimulus (SD ) here

14. “Mr. Shallow” example…
“Mr. Shallow” moves to a new city and starts hitting the singles bars seeking a new partner
According to the peak shift, what type of woman will he be trying to “hook up” with???

15. Stimulus Control: Multiple Schedules
A multiple schedule is a complex schedule of reinforcement
It is like a chained schedule except that each link is reinforced
A multiple schedule consists of 2 or more simple schedules presented in sequence, each resulting in reinforcement and each having a distinctive SD

16. Stimulus Control: Behavioral Contrast
Behavioral contrast is a change in a reinforcer’s effectiveness caused by previous experience with other reinforcers
The change may be due to the schedule of reinforcement or the magnitude of the reinforcer
Positive contrast occurs when the previous reinforcer was less valued (current reinforcer’s effectiveness is increased)
Negative contrast occurs when the previous reinforcer was valued more (current reinforcer’s effectiveness is decreased)

17. Crespi (1942)

18. Stimulus Control: Behavioral Contrast
If presented a signal that indicates a change in rate or magnitude of reinforcement is about to begin, anticipatory contrast will often occur
Anticipatory contrast is a change in behavior (increase or decrease) in inverse anticipation of an upcoming change in reinforcement (decrease or increase)

19. Seems to be the case with us to right from the start…
Kobre and Lipsitt (1972)
Participants
Newborns
Procedure
Artificial nipple that either gave reinforcer of sucrose or water
Results
Support contrast effect

20. Stimulus Control: Fading & Errorless Discrimination Learning
Errorless Discrimination Learning involves setting up the discrimination training procedure in such a way that the organism learns the discrimination without making mistakes
Do all shaping (pretraining) with the SD only, which is always associated with reinforcement
Fade in the S∆ gradually (start with a weak version and work up to the final strength of the stimulus)

21. Stimulus Control: Fading & Errorless Discrimination Learning
There are fewer adverse side effects (e.g., frustration) during learning when using an errorless discrimination procedure
However, organisms are less flexible when the discrimination changes if they were trained with an errorless procedure versus the standard approach
Therefore, you should only use the procedure for factual information where the response requirements are unlikely to change

22. Haupt et al. (1975) Participant 9 year-old girl with math difficulties
Procedure
Correct answers were gradually faded out

23. Stimulus Control: Additional Applications
Training animals for public performance
Targeting
Eliminating problem behaviors in animals
Training in and/or eliminating human behaviors
Improving study habits
Reducing insomnia

24. Credits: