PSY402 Theories of Learning

1. PSY402Theories of Learning Chapter 7 – Stimulus Control

2. For Midterm 2 • As stated in class, Chapter 7 will be on the next midterm. • The slide in the Chap 5 materials stating that Chap 7 would not be on the midterm is incorrect (leftover from a previous quarter). • It has now been deleted from the set of slides. • Please send me an email if you have any questions about what the next midterm will cover.

3. The Role of Environmental Stimuli • In operant conditioning, the stimulus becomes associated with the reinforcer or punishment. • Reward or punishment is the UCS. • The stimulus signaling reward or punishment is the CS. • The CR motivates operant behavior. • Responding can be used as a measure of the strength of a CR.

4. Definitions of Terms • Stimulus control -- Environmental stimuli signal the opportunity for reward or punishment. • Generalization – responding in the same way to similar stimuli. • Discrimination – responding to some stimuli but not to others.

5. Generalization Gradient • Degrees of generalization occur. • In some situations, the same response occurs to similar stimuli. • In other situations, the amount of response varies with the similarity. • Generalization gradient – a graph showing how the strength of response changes with similarity. • Steep gradients mean narrow response (stimuli must be very similar).

6. Kinds of Gradients • Excitatory conditioning (S+) – a CS-UCS response to a stimulus is learned. • Excitatory gradient – the S+ is varied and the CR is measured. • Inhibitory conditioning (S-) – a CS signals absence of the UCS and thus inhibits the CR. • Inhibitory gradient – the S- is varied and the CR is measured.

7. Shapes of Gradients • Most sensory stimuli produce similar gradients. • Pigeons pecking at colored lights. • Tones paired with shocks. • Words paired with pretzels or candy: • Synonyms and homonyms produce salivation. • Semantic similarity works best.

8. Flat Gradients • A flat gradient means all stimuli are being responded to as if they were the same. • Responding with a gradient to a tone occurred only when the tone signaled reward during training.

9. Generalization of Inhibition • Inhibition example: fear of dating. • A good experience leads to less fear of dating a different person. • Inhibition gradients are similar to excitatory gradients – the more the stimulus varies, the less inhibition.

10. Explanation • Lashley-Wade theory – people and animals generalize because they are unable to discriminate. • Can’t tell the difference between stimuli • A contrast is needed during training to enable discrimination. • Discrimination training leads to steeper generalization gradients. • Perceptual experience matters.

11. Discrimination Learning • Important to recognize when reinforcement is not available so that responding can be withheld. • Discriminative stimulus: • SD – reinforcement is available (S+) • SD – reinforcement is unavailable (S-) • Conditioned stimuli always produce a response. Discriminative stimuli signal the opportunity to respond.

12. Two-Choice Discrimination Tasks • The discriminative stimuli are on the same dimension: • Red vs green light. • Need not be presented simultaneously. • Two-choice discrimination includes one SD and one SD . • Other tasks can use multiple multiple SD or multiple SD.

13. Three Phases • Subjects begin by responding equally to both stimuli – prediscrimination phase. • Discrimination phase -- with training, response to SD increases and response to SD declines. • Shift back to non-differential reinforcement to show that behavior was caused by reinforcement.

14. Conditional Discrimination • Availability of reinforcement depends on the condition of a stimulus. • The stimulus does not always signal the same thing. • More difficult to learn. • Nissen’s chimpanzees: • Large, small squares, white or black. • SD = large white, small black.

15. Behavioral Contrast • Behavioral contrast – the increased responding to the differential stimulus, decreased response to SD • Contrast also occurs with changes in the duration of reinforcement. • VI-10 to VI-3 • Local contrast – emotional • Sustained contrast – related to the differential reinforcement.

16. Anticipatory Contrast • Williams – sustained contrast occurs due to anticipation of a future reinforcement contingency. • Not due to recall of past contingency. • VI-3, VI-6, VI-3 • Compare the first and third VI-3 behavior. • VI-6 affected the first VI-3 more than the last VI-3 -- a prospective effect.

17. Occasion Setting • A conditioned stimulus (CS) can create the conditions for operant responding to a second conditioned stimulus (CS). • Occasion setting – ability of one stimulus to enhance the response to another stimulus. • The facilitating stimulus does not produce a CR by itself.

18. SD as an Occasion Setter • A Pavlovian occasion-setter can increase operant responding. • Example: • A meal elicits CR craving for cigarette. • Requesting a cigarette after a meal – an operant behavior caused by CR. • Conditional occasion-setting: • Second stimulus modifies meaning of first discriminative stimulus.

19. Conclusions • An occasion-setter can increase operant responding. • A discriminative stimulus (SD) can increase response to a CR (Pavlovian conditioning). • This implies interchangeability of Pavlovian occasion-setters and discriminative stimuli.

20. Central Motivational States • Conditioned stimuli influence operant behavior through their effect on motivational states: • Appetitive • Aversive • Emotional responses influence operant behavior.