Avoidance learning

Avoidance training belongs to negative reinforcement schedules. The subject learns that a certain response will result in the termination or prevention of an aversive stimulus. There are two kind of commonly used experimental settings: discriminated and free-operant avoidance conditioning.

Discriminated avoidance Conditioning

In discriminated avoidance conditioning, a novel stimulus such as a light or a tone is followed by an aversive stimulus such as a shock (CS-US, similar to classical conditioning). Whenever the animal performs the operant response, the CS(conditioned stimulus) respectively the US(unconditioned stimulus)is removed. During the first trials (called escape-trials) the animals usually experiences both the CS and the US, showing the operant response to terminate the aversive US. By the time, the animal will learn to perform the response already during the presentation of the CS thus preventing the aversive US from occurring. Such trials are called avoidance trials.
Free-operant avoidance learning

In this experimental session, no discrete stimulus is used to signal the occurrence of the aversive stimulus. Rather, the aversive stimulus (mostly shocks) are presented without explicit warning stimuli.

There are two crucial time intervals determining the rate of avoidance learning. This first one is called the S-S-interval (shock-shock-interval). This is the amount of time which passes during successive presentations of the shock (unless the operant response is performed). The other one is called the R-S-interval (response-shock-interval) which specifies the length of the time interval following an operant response during which no shocks will be delivered. Note that each time the organism performs the operant response, the R-S-interval without shocks begins newly.

Two-process theory of avoidance

This theory was originally established to explain learning in discriminated avoidance learning. It assumes two processes to take place . a) Classical conditioning of fear During the first trials of the training, the organism experiences both CS and aversive US(escape-trials). The theory assumed that during those trials classical conditioning takes places by pairing the CS with the US. Because of the aversive nature of the US the CS is supposed to elicit a conditioned emotional reaction (CER) - fear. In classical conditioning, presenting a CS conditioned with an aversive US disrupts the organism's ongoing behavior. b) Reinforcement of the operant response by fear-reduction Because during the first process, the CS signaling the aversive US has itself become aversive by eliciting fear in the organism, reducing this unpleasant emotional reaction serves to motivate the operant response. The organism learns to make the response during the CS thus terminating the aversive internal reaction elicited by the CS. An important aspect of this theory is that the term "Avoidance" does not really describe what the organism is doing. It does not "avoid" the aversive US in the sense of anticipating it. Rather the organism escapes an aversive internal state, caused by the CS.

One of the practical aspects of operant conditioning with relation to animal training is the use of shaping (reinforcing successive approximations and not reinforcing behavior past approximating), as well as chaining.

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