Chapter 3 Two Early Connectionist Theories

1. Chapter 3Two Early Connectionist Theories Presented By: Shayna N. Lamkin

2. Chapter Highlights * Introduction * Pavlov’s Conditioning * Basic Principles of Pavlovian Conditioning * Excitation and Inhibition * Applications and Implications * Thorndike’s Early Connectionism * Thorndike’s Basic Ideas * Elaborations * Comparison of Thorndike with Pavlov * Thorndike’s Place in Psychology

3. Introduction First Psychological laboratory was founded by Wilhelm Wundt in Germany, 1897. *A marking point at which modern scientific psychology was placed on a definite institutional footing. Wundt and his colleagues wanted to understand human sensations and thoughts and feelings. They wanted to take the continuous flux of conscious awareness and analyze it into its basic components.

4. *Are memory images the same as sensations? *Are feelings a special kind of sensation or are they something really different? *How is the intensity of a sensation related to the intensity of the physical stimulus that produces it?This kind of psychology, developed in Germany, became to a great extent the standard for the rest of Europe and for America.

5. Pavlov’s Conditioning 1904-Ivan P. Pavlov (1849-1936) won the Nobel Prize in physiology and medicine for his work on digestion. His research consisted of opening a fistula in the wall of a dog’s stomach. He noticed that the stomach secretions he was studying were first triggered not by food reaching the stomach but by chewing or even just the sight of food, and he began to find this anticipatory secretion the most interesting aspect of the digestive process. Through this new line of research (Pavlov 1960, original date 1927), he became even more famous as the father of conditioning.

6. The experimenter starts with a stimulus (the unconditioned stimulus) that will reliably elicit a specific response (the unconditioned response). Pavlov’s research-the unconditioned stimulus was meat powder and the unconditioned response was salivation. What was to become the conditioned stimulus could be any of great variety of stimuli: a bell, a ticking metronome, a triangle drawn on a large care, and so on… If this stimulus was presented repeatedly just before the meat powder, it too came to elicit salivation, the conditioned response, and it thus became a conditioned stimulus.

7. Since the term conditioning came to be applied quite broadly, this particular kind of conditioning, being first studied, came to be called classical conditioning. The terms unconditioned stimulus and conditioned stimulus may seem a bit odd, considering what they mean. What is meant is that they mean is unconditional stimulus (not conditional on any previous training), while the bell (or whatever stimulus precedes the meat) is a conditional on having been paired with the meat. **Emphasizing that although Pavlov’s own studies mostly used food as the unconditioned stimulus, there was no such limitation either in his theory or in other research on Pavlovian conditioning.

8. Unpleasant (or noxious) stimuli have been used as unconditioned stimuli as much as have pleasant ones. **Examples range from disliking a food because eating it followed by illness, to hating a person who mistreated you, to being afraid of horses after being thrown by one.

9. Basic Principles of Pavlovian Conditioning The most basic principle of Pavlovian conditioning is that the more often the conditioned stimulus has been presented just before the unconditioned stimulus, the greater is the tendency for the conditioned stimulus to produce the conditioned response. The resulting change indicates the acquisition of conditioning. This change represents two laws of acquisition, one stating that with more pairings of the conditioned and the unconditioned stimulus, the probability that a conditioned response will occur increases, and the other stating that the size of the conditioned responses increases (in Pavlov’s research, the number of drops of saliva).

10. A second basic principle of conditioning is extinction. Extinction means that after acquisition, the more successive times the conditioned stimulus is then presented without the unconditioned stimulus, the weaker the tendency to make the conditioned response will become. As with acquisition, this law is really two laws, one stating that the more times in succession the conditioned stimulus has been presented alone, the smaller the conditioned response will be, and the other stating that the more such presentations there have been, the less often any conditioned response will occur when the conditioned stimulus is presented. Extinction might thus be considered simply a process of unlearning the conditioning.

11. Two other principles of conditioning are very basic. One is generalization. This means that after conditioning, the dog will make the conditioned response not only to the exact conditioned stimulus with which it was trained, but also to the other stimuli that resemble its. Another principle is discrimination, which is related to generalization in much the same way that extinction is to acquisition. Discrimination requires training with two conditioned stimuli, one of which is always followed by the unconditioned stimulus (as in acquisition) an the other never followed by it (as in extinction). As training continues, there will be less and less conditioned responding to the one not followed by the unconditioned stimulus, until eventually there is none.

12. Excitation and Inhibition Pavlov suggested that the laws of conditioning could be explained by the joint actions of two main processes in the brain: excitation and inhibition. Excitation is a process of arousal, one that tends to make responses happen, whereas inhibition is a process of suppression, one that tends to prevent responses from occurring. Both therefore operate in opposition to each other. Of the two, excitation plays a much greater part in producing conditioning, but inhibition is needed to explain many of the specific ways in which conditioning works.

13. An example of conditioning, in which a bell as the conditioned stimulus is presented to the dog just before meat is presented as the unconditioned stimulus. Both of these stimuli produce excitation in the cerebral cortex of the brain, each at a particular spot in the cortex appropriate to that stimulus. Since the food is something important to the dog’s survival, whereas the bell is a biologically less important stimulus, the excitation produced by the food is the stronger of the two.

14. According to Pavlov, excitation is then drawn from the location of the cortex where the bell is represented to the location where the food is represented. This effect occurs, he said, because of two general tendencies. One is the tendency for weaker excitation to be drawn toward the location of stronger excitation. The other is the tendency for excitation that occurs first to be drawn toward the location of excitation that occurs slightly later. Each time the bell is presented just before the food, the excitation from the conditioned stimulus is drawn to the location of the excitation from the unconditioned stimulus, and as a result the connection between these two regions in the cortex gets stronger.

15. Excitation, Pavlov said, will occur not only at the place of the cortex appropriate for the conditioned stimulus, but also at the place where the unconditioned stimulus is represented. This excitation, in turn, will produce a response similar to the unconditioned response. Excitation, he said also has an automatic tendency to irradiate-that is, to spread out from its original focus in all directions over the surface of the cortex. The ideas of Pavlov’s was based on direct physiological information.

16. Applications and Implications Pavlov believed that the principles of conditioning could be used to explain a variety of phenomena. He related these principles to personality, considering that one of the most fundamental differences among dogs-and among humans-is the balance between excitation and inhibition. Excitatory personalities tend toward too much unrestrained activity (“When in doubt, do something, do anything!”), whereas inhibitory personalities tend toward unresponsiveness (When in doubt, the safest thing to do is nothing.”). Pavlov considered conflict between excitation and inhibition to be the basis of neurosis.

17. Consider the case of the dogs that had learned a discrimination between a circle followed by food and an ellipse followed by no food. After they had learned, on further trials the ellipse was gradually changed in shape to resemble more and more closely a circle, so that it was harder and harder to make the discrimination, until finally it became impossible to see any difference between the two stimuli and the discrimination broke down completely. As a result, the dogs had both excitatory and inhibitory tendencies toward the seemingly identical figures, and no way to tell which tendency was appropriate. Pavlov noted that excitatory dogs would respond to both stimuli, inhibitory dogs to neither.

18. This failure to discriminate was not just a calm adoption of the same response to both stimuli. Rather, the dogs barked, tried to leave the experimental room, and generally appeared anxious, frustrated, and upset. These symptoms seemed so similar to those of humans in difficult conflict situations that Pavlov labeled the syndrome experimental neurosis. Interceptive conditioning, in which either the conditioned or the unconditioned stimulus, or both, is presented directly to one of the internal organs. The responses that get conditioned by such interceptive stimulation are also responses of the internal organs or their blood supplies.

19. Example-Cold water as the unconditioned stimulus can make the blood vessels in the wall of the stomach constrict, and this unconditioned response can then be trained as a conditioned response to some conditioned stimulus. Such conditioning brings unconscious bodily processes. Semantic conditioning, the conditioning of meaning… or conditioning in which the conditioned stimulus is verbal and the effect of the conditioning is to modify its meaning for the learner. Whereas bells and lights and other such conditioned stimuli make up a first signaling system, language, Pavlov said, becomes a second signaling system.

20. Thorndike’s Early Connectionism The idea that pleasure and pain are important determiners of behavior has a distinguished history in psychology. It forms the basis of the theory of psychological hedonism that was developed by the English philosopher Jeremy Bentham in the eighteenth century and adopted by a number of other British philosophers. According to this view, we all do those things that give us pleasure and avoid those that give us pain. However, it remained for Edward L. Thorndike (1874-1949) to make a similar, more behavioristic view central to the psychology of learning.

21. Thorndike was a pioneer in experimental animal psychology. Instead of relying on stories about the intelligent feats of this or that animal, he took animals into the laboratory, presented them with standardized problems, and made careful observations of how they solved their problems. “Animal Intelligence” (1898), his monograph, is still one of the classics in the field. His most widely quoted studies involved cats in a problem box. A hungry cat was confined in a cage with a tempting morsel of fish outside. The cat could open the door by pulling a loop of string hanging inside the cage. Usually a cat went through a long process of walking around, clawing the sides of the cage, and other responses before it pulled the loop of string and was able to leave the cage.

22. On successive tests in the cage, the cats took shorter and shorter times to pull the string. Even after several experiences of opening the door by pulling the string, on a given trial a cat would still spend considerable time in other behavior before pulling the string. This led Thorndike to conclude that the cat’s learning to pull the string involved not an “intelligent” understanding of a relation between string and pulling and door opening but a gradual “stamping in” of the stimulus-response connection between seeing the string and pulling it. At the time Thorndike published these studies, they were radical in two respects: their careful observation of animal behavior under controlled conditions and their concern with the gradual strengthening of responses.

23. They were Thorndike’s answer to the argument about whether animals solve problems by reasoning or by instinct. By neither, said Thorndike, but rather by the gradual learning of the correct response.

24. Thorndike’s Basic Ideas The question on whether what animals and people learn is connections or cognitions, Thorndike was firmly on the connectionist side. Some of Thorndike’s views on learning had changed during the course of his career, one that did not change was his conviction that what we learn are stimulus-response bonds. These bonds, in his view, were connections in the nervous system between incoming stimuli and the responses that those stimuli produce. He did not use the term “intervening variables,” but he treated these bonds as intervening variables in his interpretation of learning. Why does a given stimulus produce a given response rather than some other response, or none? Because there is a bond between that stimulus and that particular response.

25. The question is “What does learning consist of?” The forming and strengthening and weakening of these stimulus-response bonds. His theory is thus a clearly connectionist theory. The other question-”What part does reinforcement play in the formation of these bonds?” Thorndike was again clear: it plays a crucial role. His primary law of learning was the law of effect. This law states that in order for a stimulus-response bond to be formed or s strengthened, the response must occur in the presence of the stimulus and then be followed quickly by a satisfier (reinforcer). In other words, making that response in the presence of that stimulus must have a satisfying effect; hence the name, law of effect.

26. Likewise, if the response occurs in the presence of the stimulus but is followed by an annoyer, the stimulus-response bond will be weakened. The fact that satisfiers and annoyers are essential elements in the learning process, according to Thorndike, make his, in addition to being a connectionist theory, a reinforcement theory as well. Thorndike’s emphasis here was heavily on what the cats did, rather than on what they thought or felt, in other words, on their behavior. His use of the terms satisfier and annoyer may seem too subjective for such an objective approach. However he defined those two words in a quite objective way.

27. “By satisfying state of affairs is meant one which the animal does nothing to avoid, often doing things which maintain or renew it. By an annoying state of affairs is meant one which the animal does nothing to preserve, often doing things which put an end to it”-Thorndike Thorndike says nothing here about the animal’s feelings, only about what the animal does. If satisfiers give the animal pleasure or annoyers give it displeasure, that is not part of Thorndike’s theory, which defines satisfiers and annoyers by their effects on the animal’s behavior, not on its feelings.

28. Later on, Thorndike modified the law of effect to make satisfiers much more important than annoyers. Reward, he decided, strengthens connections, but punishment does not directly weaken them. If punishment is effective in weakening the tendency to do something, it is primarily because it makes behavior more variable and thus gives some new response a chance to be rewarded. He based this change in interpretation on a variety of animal and human research, including analysis of biographical information. Thorndike’s view that reward strengthens behavior directly whereas punishment weakens it indirectly has been accepted by a number of subsequent psychologists.

29. Elaborations Thorndike believed firmly throughout his career that the strengthening of stimulus-response bonds by satisfiers is central in all learning. When he began his research with animals, he regarded the sort of trial-and-error learning described above as only one of several possibilities. From consulting with various experts on animal training, he expected that his cats would learn faster to pull the loop of string if he held the cat’s paw in his hand, moved it so that it pulled the loop of string down, and thus showed the cat that the door of the cage would then open and let the cat out to where the food was.

30. However, his research eventually convinced him that neither of these methods would work, that animals would learn only by trying various responses, being reinforced for only one of them, and thereby gradually learning the successful response. Though subsequent researchers have had some success with the other two methods-passive movement and imitation-the question of how widely they occur when the experiment is done appropriately is still being argued. In Thorndike’s career, he stated a number of laws of learning, of which the law of effect is by far his best known. One of the others was the law of exercise, which stated that a stimulus-response bond was strengthening from the addition of reinforcement.

31. To the extent that this law of exercise was valid, then the law of effect would refer only to the additional strengthening from the addition of reinforcement. However, his research suggested that any strengthening of a bond by practice alone, without reinforcement, was quite small. The law of exercise thus became less important in his theory, overshadowed by the law of effect. Nevertheless, it retained some importance as a factor in memory, where repeatedly saying two words together would strengthen the tendency to remember one when hearing the other, even without any obvious satisfier following it. Thus Thorndike, though he stated and enthusiastically advocated the law of effect, did not completely rule out learning in the absence of reinforcement.

32. Thorndike’s concern with education led him to take considerable interest in the topic of transfer, the effect of learning one thing on subsequently learning something else. Usually the transfer is positive, meaning that the second learning is more rapid than it would be without the first learning, though sometimes the first learning interferes with and slow down the second, which constitutes negative transfer. In Thorndike’s time it was widely believed that certain difficult subjects learned in school-Latin and math were favorite examples-produced positive transfer to a wide variety of other learning, much as though they were strengthening the brain by exercising it, or at least teaching the student to think logically in some very general way.

33. The truth or falsity of this belief was obviously important to educators and Thorndike set out to test it. He concluded that learning any material transfers to learning any other material only the degree that the two overlap. Thorndike’s considerable influence in educational circles thus came out in favor of teaching students the specific knowledge and skills they would need, rather than other knowledge and skills designed to produce general mental improvement.

34. Comparison of Thorndike with Pavlov • Both set out to study learning in an objective, scientific way. • Both analyzed not only learning but all behavior into responses to stimuli. • Both put a good deal of emphasis on studies of animals, but were nonetheless strongly concerned with applying what they learned to the betterment of humankind. • They were also marked similarities in the laws of learning that they proposed. • Both saw gradual strengthening of stimulus-response connections. • Both noted that when this reinforcement was removed, the learned response was extinguished.

35. Their systems differed in at least two ways. One is the type of learning on which they focused. In Pavlovian conditioning, a new stimulus (the conditioned stimulus) comes to elicit a response that is very similar to the one already elicited by the unconditioned stimulus…a new stimulus comes to elicit an old response. For Thorndike’s cats, the new behavior of pulling the loop of string was learned as a response to the same stimuli of the puzzle box that had been there all along-an old stimulus became attached to a new response.

36. Pavlov considered it of major importance to figure out what was happening in the cerebral cortex during conditioning. Thorndike was little concerned with the underlying physiology. He assumed that stimulus-response bonds represented some reality in the nervous system, but it did not matter to him what in particular was going on in the brain as these bonds were strengthened and weakened. This distinction is not particularly important. Both Pavlov and Thorndike were using intervening variables inferred from behavior, and their value lies in how adequately they explained the behavior.

37. Thorndike’s Place in Psychology Thorndike was a man of great energy and of wide interests within psychology. He was a pioneer not only in both animal and human learning but also in the psychology of education and of individual differences. In all of these areas he was interested both in pure science and in applications, and his contributions included methods, theory, and data. There are thus a number of aspects of American psychology for which a look at Thorndike’s work makes a reasonable starting point. Instead what he did most effectively for the development of learning theory was to provide a few strong, simple ideas for subsequent psychologists and educators to use, build on, or in some cases reject.

38. For well over half of the century since he published his 1898 monograph on animal learning, the majority of American learning theorists have followed his lead, making Thorndike’s pioneering ideas more precise.