Chapter 10

Aversive Control:

Avoidance and Punishment

Appetitive Aversive

PositiveContingency(R produces O)

NegativeContingency(R prevents O)

Instrumental Conditioning Procedures

PositiveReinforcement

Response increases

Punishment

Response decreases

OmissionTraining

Response decreases

NegativeReinforcement

Response increases

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

Aversive Control

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 anaversive 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 responseduring 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 safter 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 ofthe 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

20

40

60

80

100

Days

Classical Avoidance

Percentage of CRs

These results showed that avoidance conditioning is different thanstandard classical conditioning

The Discriminated Avoidance Procedure

CS

US

R

Avoidance Trial

CS

US

R

Escape Trial

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 conductedin a shuttle box

the shuttle box consists of 2 compartments separatedby 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 shockis 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 contingencybetween a response and an aversive stimulus

The absence of the aversive stimulus is presumably thereason 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) US (shock) UR (fear)

CR (fear)

Now, the subject can be negatively reinforced during the warning stimulus; this is the second, operant conditioning process

R CSRemoves

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.

The Two-Process Theory of Avoidance

Support for Two-Process Theory of Avoidance

Acquired-Drive Experiments

If Two-Process theory is right, then separating the two processes should still lead to successful learning.

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)?

Two phases to 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

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 itoff by crossing to the other side (no shocks presented) how long the rats took to cross the shuttle box and turn off theCS 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

However, the level of fear is not always positively correlated with avoidance

If fear motivates and reinforces avoidance responding,then the conditioning of fear and the conditioning of instrumental avoidance behavior should be highly correlated

Animals often become less fearful as they become moreproficient 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 suppressionprocedure 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 CSin a shuttle-box training was continued for separate groups until they avoidedthe shock on 1, 3, 9 or 27 consecutive trials the animals were then returned to the Skinner box for barpressing the CS that had been used in the shuttle box was periodicallypresented to see how much suppression of bar pressing it wouldproduce

Kamin, Brimer, & Black (1963)Results: figure 10.7

-.20

-.15

-.10

-.05

0

1 3 9

Adjustedsuppressionratio

27

Avoidance criterion

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 suppressionto the avoidance CS than those trained to a criterion of 9 consecutive avoidances

This suggests that fear, as measured by conditionedsuppression, decreases during extended avoidance trainingHowever, this decrease in fear is not accompanied by adecrease 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 isomitted on that trial this is an extinction trial for the conditioned fear response repetition of the avoidance response (and thus the CS-aloneextinction trials) should lead to extinction of fear as the CS becomes extinguished, there will be less reinforcementresulting from the reduction of fear, and the avoidance responseshould 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 potentialfor reinforcement through fear reduction, thereby reconditioningthe 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

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).

Free-operant avoidance

also called nondiscriminated avoidance or Sidman avoidance

shock postponement procedure no warning signal

Problem for two-process theory?