The science of life : fully illustrated in tone and line and including many diagrams, стр. 800

BOOK 8

can discern in the dog’s mind the same essential processes that we use when we learn alanguage. ‘The animal can be taught that particular combinations of sounds have special meanings, and to associate simple responses with them. Everybody knows that a dog will learn its own name and one or two simple commands such as “ heel ”’ or “down.” Sometimes one hears of dogs which have exceptional ability in this respect. A couple of years ago a report appeared signed by Drs. Warden and Warner of the Department of Psychology at Columbia University. It concerned a male German shepherd dog called Fellow, owned by Mr. Herbert, of Detroit, Michigan, who had been at great pains to teach it to respond to a number of verbal commands. The tests were performed with the master out of the room, to exclude any involuntary gesture which might convey to the dog what was expected of it, and nevertheless it would obey such shouted commands as “ turn your head,” “ look up high ” or “ roll over.” The psychologists report that ‘‘ there would seem to be no doubt that scores of associations between verbal stimuli and definite responses have been well fixated by the patient teaching of Mr. Herbert during the past several years.”

The second element in the dog which foreshadows our own power of languagebuilding is the formation of chains of conditioned reflexes—but this is a more complicated story. It depends upon the fact that one originally neutral stimulus can be “ associated’? with another which has already acquired a conditioned meaning, as the following example from Pavlov’s laboratory illustrates.

A dog is taught by the method described above that the clicking of a metronome means food; and now that sound is itself enough to evoke typical expectation signs. After this state of affairs has been established, the following sequence of events is arranged : first a large black square appears in front of the animal and then it vanishes again. Ten seconds later the metronome begins to click, and at once the dog salivates and licks its lips—but this time no food appears. ‘This new sequence is repeated several times, being interspersed with the more normal procedure of metronome followed by food. The ultimate result is that the black square gets “associated? in the dog’s mind with the metronome ; it is a signal that foreruns the metronome, and since the latter is a food-signal the former becomes a foodsignal, too. So presently the black square

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THE SCIENCE OF LIFE

CHAPTER 6

by itself comes to evoke signs.

But this is a tricky experiment to perform. If the interval between black square and metronome is too short, or if they are applied together, a different thing happens ; the dog discriminates, and comes to respond to the metronome by itself but not to the metronome heralded by the black square. With this complication we shall deal more fully shortly. When the experiment is successful as we first described, it is evident that a conditioned reflex can be built up not only on the basis of a natural reflex but on the basis of another conditioned reflex, too. We can condition a conditioned reflex ; we can set up a conditioned reflex of the second degree. And we can proceed to condition that. In the brain-switchboard an arriving impulse may be made to pass not merely along a single connection between two points but along a whole chain of connections between different points before it is sent down to the lower centres again. In this special case of the square and the metronome two connections have been made, and the impulses sent up from the retina when the black square is seen are sent from the eye-centres in the brain to the ear-centres which would be stimulated by the metronome, and thence to the areas from which fibres run to the salivary and gastric glands and muscles of lip-licking, tail-wagging, and so forth.

Now this is, in embryo so to speak, what we do when we learn a language. At first We associate particular noises with particular experiences ; these are simple conditioned reflex mechanisms. Then we begin to build word on word, to learn them not by actually experiencing their meaning but by description ; and here chains of conditioned reflexes are built up and come into play. The process is, of course, a vastly complicated one, enormously more complicated in our case than anything a dog can do, and the inhibitions that we are about to discuss play an important part in it. Nevertheless, what happens is fundamentally the same thing ; it is no more than an elaboration of the cruder, simpler “learning” that was studied by Pavlov in his dogs.

So we begin to realize the conditioned reflex as the unit of which our higher mental activities are built up. When we perform such complicated automatic acts as standing erect or walking, we do so as a result of the interplay of a great number of inborn reflexes. We might call such an activity a symphony of simple reflexes. When we

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