Transcript Chapter 10
Chapter 10 Aversive Control: Avoidance and Punishment Instrumental Conditioning Procedures Appetitive Positive Contingency (R produces O) Negative Contingency (R prevents O) Positive Reinforcement Response increases Omission Training Response decreases Aversive Punishment Response decreases Negative Reinforcement Response increases Aversive Control Negative reinforcement – also called escape/avoidance Avoidance procedures increase the operant response Punishment procedures decrease the operant response With both types of procedures, the behavior that develops serves to minimize contact with the aversive stimulus Critical difference: • in avoidance, taking a specific action prevents the aversive stimulus • in punishment, refraining from action minimizes contact with the aversive stimulus Aversive Control Avoidance behavior is sometimes referred to as active avoidance Punishment is sometimes referred to as passive avoidance Both terms emphasize the fact that both avoidance and punishment involve minimizing contact with an aversive stimulus Avoidance Behavior origins in Pavlovian conditioning first experiments conducted by Bechterev (1913) Participants instructed to place a finger on a metal plate A warning stimulus (CS) was then presented, followed by a brief shock (US) The participants quickly lifted their finger off the plate after being shocked After a few trials, they also learned to make the response during the CS This experiment viewed as a standard example of Pavlovian conditioning Avoidance Behavior In the 1930s people focused on the difference between a standard classical conditioning procedure and a procedure that had an instrumental avoidance component added Brogden, Lipman, & Culler (1938) • Tested 2 groups of guinea pigs in a rotating wheel • A tone served as the CS and a shock as the US • The shock stimulated the animals to run and rotate the wheel • For the classical conditioning group, the shock was presented 2 s after the onset of the tone • For the avoidance conditioning group, the shock also followed the tone when the animals did not make the CR (a small movement of the wheel) • if the avoidance animals moved the wheel during the tone CS before the shock occurred, the scheduled shock was omitted Brogden, Lipman, & Culler (1938) Results: Figure 10.2 Classical Avoidance 100 80 Percentage 60 of CRs 40 20 Days These results showed that avoidance conditioning is different than standard classical conditioning The Discriminated Avoidance Procedure Avoidance Trial Escape Trial CS CS US US R R Discriminated, or Signalled, Avoidance A warning stimulus (e.g., a light) signals a forthcoming SAversive (e.g., a shock) If the required response is made during the light (warning stimulus), before the shock (SAversive) occurs, the subject avoids the shock. If a response is not made during the warning stimulus of the light, the shock (SAversive) occurs, and terminates when the required response is made (i.e., escape). Discriminated, or Signalled, Avoidance Discriminated avoidance procedures are often conducted in a shuttle box the shuttle box consists of 2 compartments separated by a barrier the animal is placed on one side of the apparatus at the start of the trial, a CS is presented if the animal crosses to the other side before the shock is presented, then no shock occurs and the CS goes off after the inter-trial interval, the next trial can be started with the animal in the second compartment shuttle avoidance two-way shuttle avoidance or one-way shuttle avoidance (one-way avoidance easier to learn) The Two-Process Theory of Avoidance Avoidance procedures involve a negative contingency between a response and an aversive stimulus The absence of the aversive stimulus is presumably the reason that avoidance responses are made But, how can the absence of something provide reinforcement for instrumental behavior? The Two-Process Theory of Avoidance Explains avoidance learning in terms of two necessary processes: First, the subject learns to associate the warning stimulus with the SAversive – what is this? This is a classical conditioning process; the warning stimulus of the light is the CS, the SAversive of shock is the US. CS (light) CR (fear) US (shock) UR (fear) The Two-Process Theory of Avoidance Now, the subject can be negatively reinforced during the warning stimulus; this is the second, operant conditioning process R Removes CS i.e., reduces fear Strengthens Thus the two-process theory reduces avoidance learning to escape learning; the organism learns to escape from the CS and the fear that it elicits. Support for Two-Process Theory of Avoidance Acquired-Drive Experiments In the typical avoidance procedure, classical conditioning of fear and instrumental reinforcement through fear reduction occur intermixed in a series of trial If Two-Process theory is right, then separating the two processes should still lead to successful learning. Two phases to acquired-drive experiments: First, classical conditioning to acquire fear of CS Second, escape training with CS as SAversive; will the subject learn a response to escape from just the CS (i.e., US no longer presented)? Acquired-Drive Experiment Brown & Jacobs (1949) tested rats in a shuttle box in phase 1 (classical conditioning), rats confined to one side of the apparatus and given 22 CS-shock pairings in phase 2 (instrumental conditioning), rats were placed on one side of the apparatus with the center barrier removed the CS was presented and remained on until the rat turned it off by crossing to the other side (no shocks presented) how long the rats took to cross the shuttle box and turn off the CS was measured for each trial Brown & Jacobs (1949) Results: Figure 10.6 Control Experimental Latency Trials Organisms do learn to escape from the CS, supporting the Two-Process Theory of Avoidance. Evidence that questions the Two-Process Theory of Avoidance If fear motivates and reinforces avoidance responding, then the conditioning of fear and the conditioning of instrumental avoidance behavior should be highly correlated However, the level of fear is not always positively correlated with avoidance Animals often become less fearful as they become more proficient in performing the avoidance response Kamin, Brimer, & Black (1963) If the warning signal in an avoidance procedure comes to elicit fear, then presentation of that stimulus in a conditioned suppression procedure should result in suppression of behavior Rats initially trained to bar-press for food rats then trained to avoid shock in response to an auditory CS in a shuttle-box training was continued for separate groups until they avoided the shock on 1, 3, 9 or 27 consecutive trials the animals were then returned to the Skinner box for bar pressing the CS that had been used in the shuttle box was periodically presented to see how much suppression of bar pressing it would produce Kamin, Brimer, & Black (1963) Results: figure 10.7 0 -.05 Adjusted suppression -.10 ratio -.15 -.20 1 3 9 Avoidance criterion 27 Kamin, Brimer, & Black (1963) With more extensive avoidance training, response suppression declined Animals trained until they avoided the shock on 27 consecutive trials showed less conditioned suppression to the avoidance CS than those trained to a criterion of 9 consecutive avoidances This suggests that fear, as measured by conditioned suppression, decreases during extended avoidance training However, this decrease in fear is not accompanied by a decrease in the strength of the avoidance response Asymptotic Avoidance performance Two-process theory predicts that the strength of the avoidance response should fluctuate in cycles when a successful avoidance response occurs, the shock is omitted on that trial this is an extinction trial for the conditioned fear response repetition of the avoidance response (and thus the CS-alone extinction trials) should lead to extinction of fear as the CS becomes extinguished, there will be less reinforcement resulting from the reduction of fear, and the avoidance response should also become extinguished however, when the shock is not avoided, the CS is paired with the US this should reinstate fear to the CS and re-establish the potential for reinforcement through fear reduction, thereby reconditioning the avoidance response Asymptotic Avoidance performance Thus, two-process theory predicts that after initial acquisition, the avoidance response will go through cycles of extinction and re-acquisition However, this does not always happen Avoidance behavior can be very persistent Free-operant avoidance also called nondiscriminated avoidance or Sidman avoidance shock postponement procedure no warning signal Rats given shocks according to a shock-shock (SCS) interval (e.g., a shock every 5 s) unless they make a response to delay the shock according to a response-shock (RCS) interval (e.g., 30 s). Problem for two-process theory?