I. Classical Conditioning and Instrumental Conditioning in Avoidance Learning

A. Mowrer’s Two-Factor Theory

Mowrer (1947) proposed that avoidance learning involved two processes--(1) classical conditioning and (2) instrumental conditioning.

(Part 1) Dangerous, painful, aversive stimuli (US) cause an innate fear response (UR). Other stimuli present at the time get associated with fear through classical conditioning. When these other stimuli (CSs) are encountered again, they evoke a fear response (CR).

(Part 2) The presence of fear and all of its visceral effects is aversive. Any response that removes these fear-evoking stimuli will be negatively reinforced. The avoidance response, therefore, is reinforced through instrumental conditioning.

The avoidance paradigm—Solomon and Wynne (1953)

What was a typical trial like?

What constituted a session?

Describe the behavior of the dogs.

What reinforces avoidance behavior?

It was easy to understand how the escape behavior persisted. The termination of the aversive stimulus would be rewarding. Escape behavior was maintained through negative reinforcement.

But how was the avoidance response maintained? The animal continues to respond even though it no longer receives aversive stimulation, but why?

Since the electric shock (US) was painful and produced an innate fear (UR) response (increased heart rate, sweating, etc.), the dark side became a feared stimulus (CS) that led to innate fear (CR) (increased heart rate, sweating, etc.). These visceral responses are unpleasant so any response that caused their reduction or elimination (i.e., escape or avoidance) would be reinforced. Mowrer argued that the termination or reduction of fear stimuli negatively reinforced the avoidance response.

B. Support for Two-Factor Theory

Two-factor theory predicts that the avoidance responding will be learned only to the extent that the warning signal terminates when a response is made.

Kamin (1957)--trained four groups of rats in a two-chamber avoidance apparatus

The figure shows that a significant amount of avoidance responding occurred in the first group only (response terminates signal and enables animal to avoid shock).

As predicted by two-factor theory, avoidance responding was poor in the group that was able to avoid shock but could not terminate the signal.

We know that delaying the onset of reinforcement reduces the effectiveness of reward. So it should be possible to reduce the level of reinforcement by introducing a delay between the avoidance response and termination of the feared stimulus.

4 conditions--After the avoidance response, the CS was terminated

(1) immediately

(2) 2.5 seconds after the response

(3) 5 seconds after the response

(4) or 10 seconds after the response

As predicted, the animals in the zero-delay condition successfully avoided shock on over 80% of the trials. Animals in the 10-second delay condition avoided shock on fewer than 10% of the trials.

C. Contradictory Evidence for Two-Factor Theory

D. Role of Discriminative Stimuli & Instinctive Drift