Instinctive Drift

Not only are natural behaviors easier to learn; they can override the influence the effect of more artificial, trained behaviors. For example, animals can be trained to do cute, human-like behaviors, using operant conditioning techniques. However, over time, the performance may deteriorate as bits of species-typical behaviors intrude on the performance. Breland and Breland (1961) called this "instinctive drift."

What is "prepared" learning? What was the phenomenon the Brelands called "instinctive drift"?

The Brelands trained animals for roadside tourist attractions. Using standard conditioning techniques, they trained animals to perform complex behaviors for food reinforcement. But in each case, after the behavior was established, it was disrupted by the intrusion of some instinctive behavior used by that species to gather or prepare food.

For example, they successfully taught a raccoon to deposit wooden coins into a metal container for food reinforcement. But soon the raccoon started rubbing the coins together and dipping them (not dropping them) into the container. It was performing the motor program raccoons use to "wash" food in a stream. This interfered with the trick to such an extent the Brelands had to give up on it. Instead, they trained the raccoon to "play basketball." The basketball was so large that the raccoon did not attempt to wash it.


The Brelands trained animals to do human-like tricks.

Similarly, a pig was reinforced with food for dropping large wooden disks into a piggy bank. It successfully learned this task. But soon the pig began dropping the coin on the way to the piggy bank, pushing it through the dirt with its nose, and flipping the coin up in the air. This is a species-typical behavior of pigs called rooting. Again, the intrusion of a species-typical behavior actually prevented the pig from completing its task and receiving food reinforcement.

What was strange about instinctive drift, with respect to reinforcement theory?

The Brelands recognized that the phenomenon of instinctive drift contradicted 1950s-era reinforcement theory. The species-typical behaviors appeared even though they prevented a hungry animal from getting food reinforcement. That violated the laws of learning carefully built up over half a century. Those laws asserted that behaviors followed by food reinforcement should be strengthened, while behaviors that prevented food reinforcement should be eliminated.

How did observations like this change the viewpoint of psychologists who use conditioning techniques?

Observations by people like the Brelands helped to sway American psychologists toward the viewpoint of the ethologists. Researchers who used operant conditioning techniques began to explore the relevance of species-typical behaviors and to document the importance of taking the animal's natural tendencies into account. Nowadays, behavior psychologists who use reinforcement techniques are well aware that some types of behavior (those prepared by evolution) are easier to train than others.


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Copyright © 2007 Russ Dewey