This is the 2007 version. Click here for the 2017 chapter 08 table of contents.

The Decline of Old Assumptions

A basic assumption of American comparative psychology in the middle of the 20th Century was that learning involved associations between stimuli and responses, and all associations should be made with equal ease. However, this way of looking at animal intelligence was challenged by the ethologists. Ethologists pointed out examples in which learning occurred very rapidly, or not at all, because of the implications of particular acts of learning for survival of the species.

Tinbergen's experiment with the digger wasp

What was Tinbergen's experiment with the wasp?

In one experiment, Tinbergen (1951) put a ring of pinecones around a digger wasp nest. The wasp spent longer than usual circling the nest when it came out of the hole, then it flew off to find food. When the wasp was gone, Tinbergen moved the pinecones, putting them around a different hole that he made by poking a stick into the ground. When the wasp returned, it went to the new hole that had cones around it.

Tinbergen pointed out the implications of this. Apparently the wasp memorized the objects in the vicinity of the nest in just a few seconds, while circling before her flight to find food.

Why would a wasp be so "smart" at memorizing objects near the nest? The answer is obvious. The wasp's survival and reproductive success depends upon this skill. The same was true of its ancestors. Digger wasps that memorized the objects near a nest could find their way back to it, reproduce, and pass on their genes (including the genes that controlled this specialized ability). This does not indicate that digger wasps are generally smarter than other insect species, just that they have a special talent adapted to their life circumstances. This is called adaptive intelligence.

Examples like the digger wasp contradict a bedrock assumption of old-time behaviorists, the idea that everything is equally easy to learn, which can be called the equivalence of associations assumption. Behavioral psychologists from Pavlov to Watson to Skinner believed that all stimuli were equal, when it came to learning. Learning was assumed to involve links or associations between stimuli and responses. Any stimulus was supposed to be as good as any other stimulus, for forming an association.

What was the equivalence of associations assumption?

By the 1970s, psychologists had awakened to the fact that not all associations between stimuli are equally easy to learn for every species. If animals are required to make a natural response to a situation, they learn quickly. If forced to make an unnatural response, they learn slowly or not at all. (Recall that this was one of Rescorla's points in Chapter 5.)

When is it difficult to condition a pigeon to peck a key?

Here is another example of how not all associations are equally easy to learn. Pigeons have a difficult time learning to peck a key to avoid a shock (Bolles, 1973, p.285). Avoidance learning is usually easy to establish, but not in this case. Pecking is a behavior associated with feeding. It is not natural for a pigeon to peck something to avoid pain. A bird's natural response to a stimulus warning of danger is to fly away. Pigeons learn very quickly, in a single trial, to fly off a perch in response to a signal predicting a shock.

On the other hand, pigeons easily learn to peck a key to get food. They even "train themselves" to peck a key for food, a phenomenon called auto-shaping. If put in an operant chamber where pecking a lighted key results in grain delivery, pigeons learn to peck the key when it lights up without any further encouragement by humans. Learning which occurs quickly and easily because of how the animal's nervous system is constructed is called sometimes called prepared learning.

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