Transcript PSY 402
PSY 402 Theories of Learning Chapter 10 – A Synthetic Perspective on Instrumental Learning Avoidance Learning Avoidance learning is puzzling because the reinforcer is not obvious. What sustains running to the other side in a shuttlebox? How can something that does not happen be a reinforcer? Mowrer’s two-factor theory was the first explanation. 10.1 The shuttlebox—an apparatus used in studies of avoidance learning in rats Side with shock Safe side Two-Factor Theory The first factor is Pavlovian fear conditioning. A light is a CS that warns of a shock. The CR is fear. The second factor is reinforcement of avoidance behavior. The avoidance response terminates the fear (CR) and the experience of relief (negative reinforcer) rewards the behavior. 10.2 The two factors in the two-factor theory of avoidance learning Acquired Drive Experiment Miller presented a shock in the presence of a white chamber. Later, rats could exit from the white side to a black side through a door. Later rats had to run in a wheel to open the door to the black side. Later rats had to press a lever to open the door to the black side. The later responses were reinforced by relief. Clinical Applications Drug-taking and alcohol use may be reinforced by escape from negative affect. People with panic disorders such as agoraphobia avoid the places that evoke anxiety. OCD hand-washing reduces fear of contamination. Bulimic purging reduces fear of getting fat. Problems with Two-Factor Theory The strength of the avoidance response should be correlated with the strength of the fear, but it is not. Dogs avoiding shock don’t look worried. Maybe after extensive training, habit takes over. Learning that turns off the CS but not the shock should reinforce behavior, but doesn’t unless it is related to an innate behavior. Learning varies with the type of response. 10.3 Fear of the warning signal declines after extensive avoidance training Fear goes away with more training More fear 10.4 A Sidman, or “free-operant,” avoidance procedure These are the responses 10.5 The effect of turning off the warning signal depends on the avoidance behavior being trained Rats find it easier to learn wheel running as an avoidance behavior Terminating the warning reinforces avoidance in both situations, but more for running the wheel 10.6 Avoidance behaviors are not equally learnable—another example of preparedness Species Specific Defense Reactions An avoidance behavior is easy to learn in the lab if it is similar to a SSDR. Thigmotaxis – wall-seeking behavior. Rats learn to jump to a platform along the wall but not in the middle of the space. Mice from Eastern vs Western Washington freeze in response to different predators. Neither freeze to garter snakes or squirrels. 10.7 Annual rainfall versus deer mice adaptation in eastern Washington Freezing is a CR (Respondent) Rats rapidly learn to freeze in order to avoid shock, but the behavior is a CR not operant. 100% of rats learned to freeze to avoid shock. Rats punished for freezing never learned not to freeze. Freezing was elicited by the punishment – the box became a CS eliciting the freezing as CR. Pavlovian learning is important to avoidance. 10.8 Freezing is actually a respondent rather than an operant (Part 1) Punishment of freezing doesn’t complete suppress the behavior. 10.8 Freezing is actually a respondent rather than an operant (Part 2) Rats stay frozen for a long time after a shock. Endorphins CS’s associated with shock also elicit endorphins (natural pain killers). These inhibit recuperative behaviors (licking a wound) that would interfere with evading a predator. The actual SSDR elicited depends on the situation as well as the species (flight, freezing, burying). Fear also inhibits pain. 10.9 Perceptual-defensive-recuperative model of fear and pain CS Termination is Important Animals are able to learn non-SSDR behaviors under certain circumstances. Termination of the CS aids such learning because it provides feedback about the correct behavior for avoidance. Feedback stimuli become conditioned inhibitors. The avoidance response becomes an inhibitor too. Not performing the response predicts the US. Expectancies About Shock Seligman & Johnston proposed that an expectancy is formed that response=no shock. This idea is inconsistent with learning theory. DeHouwer found that changing an expectancy to response=shock (when no signal is present) does not change the avoidance behavior. The idea that avoidance behavior is a negative occasion setter (response-no shock) fits better. 10.10 Shock expectancy ratings: Avoidance testing R1 or R2 mean shock when A or B are off, but no-shock when they are on. The expectancy is not associated with the key, but with the signal (A or B). Learned Helplessness Overmeier & Selgman found that dogs have difficulty learning avoidance behavior after being exposed to inescapable shock. Step 1 – expose dogs to 3 conditions: escapable shock, inescapable shock (yoke), no shock Step 2 – escape training Results – yoked dogs did not learn to escape. 10.11 The learned helplessness effect