Generalization and Discrimination

An important property of the CS and CR is known as generalization. Stimulus generalization and response generalization provide the

Fig. 6.12. Diagram of second-order conditioning. CS, conditioned stimulus; US, unconditioned stimulus.

means whereby information derived from one situation is made useful in others that are not exactly the same. Under natural conditions, animals are rarely exposed to identical stimulus events or situations; thus, the ability to generalize is a vital adaptation. Dogs easily generalize from one safe encounter with an object to many others sharing similar stimulus features. Similarly, startling or dangerous encounters are generalized with even greater facility over many objects, sometimes only remotely similar. phobias and fears are extended by generalization to include a large number of objects and situations not directly associated with the original trauma. The ability to generalize enables the animal to draw conclusions about a whole set of objects and situations without having to take the time to test each one. However, such generalizations may not hold in at least two directions: (1) Not all items sharing known safe characteristics are actually safe. (2) Not all items sharing known dangerous characteristics are actually dangerous. For example, a puppy in the habit of tugging and chewing on its leash might generalize the safety of such activities to electrical cords. The electrical cord is similar in many ways to the leash, except for one very serious difference. if the puppy is tempted and unfortunate enough to get shocked by the cord, it will quickly learn to discriminate the cord from leashes and other items sharing a similar appearance. Yet, another possible consequence of the puppy's experience might occur—the development of a fearful generalization about items sharing characteristics belonging to electrical cords. in this case, the second excess of generalization may ensue. The puppy may now incorrectly consider all items sharing characteristics belonging to electrical cords as dangerous and consequently exhibit inappropriate fear toward leashes, ropes, strings, ribbons, and the like. only through additional experience and discrimination learning will the puppy find that such items are different from electrical cords and gradually regard them as being safe. In contrast to stimulus generalization, response generalization refers to the concurrent elicita-tion of similar responses to the one being explicitly conditioned. Such generalization re sults in a loss of specificity but increases, within the confines of adaptive limits, the range of behavioral variability available to the animal.

Generalization and discrimination processes play an active role in all training activities. For example, the process of developing a conditioned reinforcer can be adversely affected by unanticipated generalization effects. A dog that has been trained to respond to the word signal "Good" as a positive conditioned reinforcer will also respond to great many other word cues spoken in a similar tone of voice. It is important, therefore, to differentiate clearly the reward cue from other voice signals used in training. Usually, a higher-pitched tone of voice is used to sound the reward cue, whereas a lower, more assertive tone is used to sound the reprimand or negative conditioned reinforcer. An alternative is to choose a conditioned reinforcer that is highly distinct and unique (e.g., a clicker or whistle).

Discriminative stimuli (SD) or command cues are customarily spoken in a normal tone of voice. Stimulus control is established by training a dog to expect reinforcement to occur if it responds appropriately in the presence of the command cue. In cases where a specific command cue needs to be discriminated from other similar verbal sounds, explicit discrimination training efforts may be needed. During such training, the range of generalization and potential confusion is reduced by selectively reinforcing only responses occurring in the presence of the specific command cue or SD. Responses occurring in the presence of similar (generalized) verbal cues are either blocked (response prevention) or extinguished by withholding reinforcement if they happen to occur. For example, in the case of the command cue "down," verbal sounds similar to "down" are presented (e.g., found, town, pound, clown, and sound) while unwanted down responses are prevented from occurring or simply not reinforced, that is, they are extinguished. This discussion anticipates a more thorough treatment of the topic of stimulus control and instrumental learning that is covered in Chapter 8.

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