The Search for Laws of Learning

Principles of classical and operant conditioning, which we reviewed in Chapter 5 (Conditioning), developed out of the search for laws of learning by early comnparative psychologists. Given such an assumption, it was reasonable to compare different species such as cats, rats, monkeys, and humans to see how quickly they learned. If they all learned in the same way, then speed of learning should be the main difference between them.

In a sense, scientists still believe that all animals learn in the same way. They all have neurons, and they all come from the same ancestral life forms on the planet earth, and they all show classical or operant conditioning effects as described in Chapter 5. We now regard the brain as modular, and we speak of multiple types of intelligence (p.94), but-except for language-those multiple forms of intelligence exist in non-human animals as well as human beings. So which is it? Do all animals learn in the same way, or not?

As you will see in this chapter, the main assumption that has changed involves specificity of associations and the adaptive nature of learning. The old-time comparative psychologists seemed to assume that any stimuli, and any responses, were equally likely to be joined through experience and learning. Their search for laws of learning was centered on finding laws of association, not on looking for differences in the content of what different species preferred to associate. Now we recognize that content matters, and different species are specialized for associating different sorts of things. That is the big change since the 1800s. See the later section on adaptive intelligence.

Thorndike's puzzle box

The American researcher Edward L. Thorndike believed learning occurred through trial and error. The animal made many responses, many of them wrong or ineffective, and eventually learned to repeat those that got desirable results. Thorndike was a mechanist, like Loeb. He felt that learning was a matter of creating associations between stimuli and responses, and no speculation about mind was necessary or useful.

What was Thorndike's puzzle box experiment? How did he interpret it?

To study trial and error learning, Thorndike used a type of test pioneered years earlier by Watson: the puzzle box. Originally, Watson's puzzle box (shown in the illustration) required a monkey to reach through the cage to lift a latch. Thorndike substituted a foot-pedal so the research could be done with cats. If the animal stepped on the switch, the door of the cage opened. The object of the research was to study how quickly the cat learned to perform this response in order to get free. Today this would be called escape learning.


Watson's puzzle box, which required a monkey to reach through the cage to lift a latch.

At first, cats put in the cage explored restlessly, meowed, but did not know how to escape. Eventually they stepped on the foot switch accidentally and the trap door opened. On succeeding trials, they operated the switch faster.

What was Thorndike's Law of Effect?

Thorndike explained learning with his Law of Effect. Animals tended to repeat a behavior that resulted in a "pleasing effect." This was an early version of the concept of positive reinforcement that B. F. Skinner used so effectively later in the century. Behavior was varied during a trial and error phase. Thorndike believed that when the animal stumbled upon a behavior that produced a desirable effect, this created a link or associative bond between a stimulus (in this case, being in the cage) and a response (stepping on the switch). Later, in the same stimulus situation, that response occurred faster.

Thorndike compared the performance of fishes, chickens, cats, dogs, and monkeys in similar tasks. Not all these species could push a foot switch, so he altered the puzzle box as needed for each species, using a response the animal could perform.

What did Thorndike find out about learning curves?

Thorndike produced a graph called a learning curve showing the number of seconds the animal took to escape on each trial. The general shape of the learning curve was similar for each species. It resembles the acquisition curve for classical conditioning from Chapter 5 and the learning curve for human motor responses in Chapter 7. In each case, the curve resembles a gentle S shape, showing that the animal does poorly at first, then "catches on" and improves its performance rapidly, until the performance reaches a maximum and levels off. In the case of the cats in Thorndike's puzzle box, each had difficulty escaping at first, but each eventually stumbled on the secret of opening the box. On succeeding trials the animal escaped faster and faster, with performance eventually leveling off when it was escaping as quickly as it could.

Thorndike found that different species varied in how fast they learned and where their performances leveled off, but each produced an S-shaped learning curve. This seemed consistent with Romanes' idea that different species learned the same way, but at different speeds.


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