[Ill.u.s.tration: Fig. 55.--Attachment of the subst.i.tute stimulus in the case of the conditioned reflex.]

At first, the child shrinks from the noise, but, the rabbit being before his eyes, he incidentally shrinks from the rabbit as well. He really shrinks in response to all the stimuli acting on him at that moment. He shrinks from the whole situation. He makes a unitary response to the whole collection of contiguous stimuli, and thus exercises the linkage between each stimulus and their joint response.

The {403} linkage between rabbit and shrinking is later strong enough to work alone. It is a clear case of the law of combination.

2. Learning the names of things.

A child who can imitate simple words that he hears is shown a penny and the word "penny" is spoken to him. To this combination of stimuli he responds by saying the word. This is primarily a response to the auditory stimulus, since the sight of the penny, though it might probably have aroused some response, and even some vocal response from the child, had no strong linkage with this particular vocal response.

But the auditory stimulus determined the response, and attracted the visual stimulus into this particular channel of saying "penny". The linkage from the sight of the penny to the saying of this word being thus strengthened by exercise, the seen penny later gives the right vocal response, without any auditory stimulus to a.s.sist.

[Ill.u.s.tration: Fig. 56.--Linkage of a name to an object. The diagram is arranged to ill.u.s.trate the formation of a linkage from the sight of the object to saying its name. A very similar diagram would ill.u.s.trate the linkage from the name to the thought or image of the object. The acquiring of mental images seems to be essentially the same process as the acquiring of conditioned reflexes, and of names.

(Figure text: object seen, various possible responses, name heard, name spoken)]

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B. Subst.i.tute Stimulus Originally an Essential Member Of A Team of Stimuli That Aroused the Response

1. Observed grouping or relationship.

"Learning by observation" is a very important human accomplishment, and we found many evidences of its importance in our study of the process of memorizing. The facts observed, which a.s.sist memory so greatly, are usually relations or groups.

[Ill.u.s.tration: Fig. 57.--The formation of an a.s.sociation between two objects by observing their grouping or relationship. (Figure text: response of observing the Group A B, thought of Group A B)]

Evidently the observation of a group of things is a response to a collection of stimuli, and could not originally be aroused by any one of the stimuli alone. The same is true of observing a relationship; the observation is a response to two things taken together, and not, originally, to either of the two things taken alone. In spite of this, a single one of the things may later call to mind the relationship, or the group; that is, it arouses the response originally made to the pair or group of stimuli. The single stimulus has been subst.i.tuted for the team that originally aroused the response. Its linkage with the response has been so strengthened by exercise as to operate effectively without a.s.sistance.

For example, in learning pairs of words in a "paired {405} a.s.sociates experiment", [Footnote: See p. 336.] the subject is apt to find some relation between the words forming a pair, even though they are supposed to be "unrelated words". When he has thus learned the pair, either of the words in it will recall the observed relation and the other word of the pair. Sometimes, after a long interval especially, the relation is recalled without the other word. One subject fixed the pair, "windy--occupy", by thinking of a sailor occupying a windy perch up in the ropes. Some weeks later, on being given the word "windy", he recalled the sailor on the perch, but could not get the word "occupy".

That is, he made the same response to "windy" that he had originally made to "windy--occupy", but did not get the response completely enough to give the second word.

In the typical cases of _a.s.sociation by contiguity_ when one object reminds us of another that was formerly experienced together with it, the law of combination comes in as just described. The two objects were observed to be grouped or related in some way, or some such unitary response was made to the two objects taken together, and this response became so linked to each of the objects that later a single one of them arouses this unitary response and recalls the other object. In the free a.s.sociation test, [Footnote: See p. 380.] the stimulus word "dimple" calls up the previously made response of seeing a dimple in a cheek, and so leads to the word "cheek". In a controlled a.s.sociation test, where opposites are required, the stimulus word "mythical" arouses the previously made observation of the ant.i.thesis of mythical and historical, and so leads to the motor response of saying the latter word.

[Footnote: When, however, this indirect linkage between stimulus and motor response is frequently exercised, short-circuiting takes place (see p. 338), and the stimulus word arouses the motor response directly. Short-circuiting follows the law of combination very nicely. Let a stimulus S arouse an idea I and this in turn a motor act M. S--I--M represents the linkages used. But undoubtedly there is a weak pre-existing linkage directly across from S to M, and this gets used to a slight degree, strictly according to the conditioned reflex diagram, with I playing the part of the effective stimulus in arousing M, and S the part of the originally ineffective stimulus.

By dint of being exercised in this way, the linkage S--M becomes strong enough to arouse the motor response directly, and I is then very likely to be left out altogether.]

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2. Response by a.n.a.logy and a.s.sociation by similarity.

When an object reminds me of a similar object, that is a.s.sociation by similarity. But suppose I actually take the object to be the similar object, and behave towards it accordingly; then my reaction is called "response by a.n.a.logy". Once, when far from home, I saw a man whom I took to be an acquaintance from my home town, and stepped up to him, extending my hand. He did not appear very enthusiastic, and informed me that, in his opinion, I had made a mistake. This was response by a.n.a.logy, but if I had simply said to myself that that man looked like my acquaintance, that would have been a.s.sociation by similarity.

Really, a.s.sociation by similarity is the more complex response, for it involves response to the points of newness in the present object, as well as to the points of resemblance to the familiar object, whereas response by a.n.a.logy consists simply in responding to the points of resemblance.

Response by a.n.a.logy often appears in little children, as when they call all men "papa"' or as when they call the squirrel a "kitty" when first seen. If they call it a "funny kitty", that is practically a.s.sociation by similarity, since the word "funny" is a response to the points in which a squirrel is different from a cat, while the word "kitty" is a response to the points of resemblance.

But response by a.n.a.logy is not always so childish or comic as the above examples might seem to imply. When we respond to a picture by recognizing the objects depicted, that is response by a.n.a.logy, since the pictured object is only {407} partially like the real object; a bare outline drawing may be enough to arouse the response of "seeing"

the object. Other instances of response by a.n.a.logy will come to light when, in the next chapter, we come to the study of perception.

[Ill.u.s.tration: Fig. 58.--Response by a.n.a.logy. The letters, A, B, X, Y, represent the several stimuli that make up the original object, and each of them becomes well linked with their common response (seeing the object, and perhaps naming it). When the linkage between X and Y and the response has become strong, a similar object, presenting X and Y along with other new stimuli, C and D, appears, and arouses the old response, by virtue of the now-effective linkage from X and Y to this response.]

[Ill.u.s.tration: Fig. 59.--a.s.sociation by similarity. Everything here as in the previous diagram, except that C and D get a response in addition to that aroused by X and Y, and so the new object is seen to be new, while at the same time it recalls the old object to mind.]

The machinery of response by a.n.a.logy is easily understood by aid of the law of combination. A complex object, presenting a number of parts and characteristics, arouses the response of seeing and perhaps naming the object. This is a unitary response to a collection of stimuli, and each of the parts or characteristics of the object partic.i.p.ates in arousing the response, and the linkage of each part with the response is thus strengthened. Later, therefore, the whole identical object is not required to arouse this same {408} response, but some of its parts or characteristics will give the response, and they may do this even when they are present in an object that has other and unfamiliar parts and characteristics.

The machinery of a.s.sociation by similarity is the same, with the addition of a second response, called out by the new characteristics of the present object.

II. SUBSt.i.tUTE RESPONSE EXPLAINED BY THE LAW OF COMBINATION

The subst.i.tute response machinery is more complicated than that of the subst.i.tute stimulus, as it includes the latter and something more.

What that something more is will be clear if we ask ourselves why a subst.i.tute response should ever be made. Evidently because there is something wrong with the original response; if that were entirely satisfactory, it would continue to be made, and there would be no room for a subst.i.tute. The original response being unsatisfactory to the individual, how is he to find a subst.i.tute? Only by finding some stimulus that will arouse it. This is where trial and error come in, consisting in a search for some extra stimulus that shall give a satisfactory response.

Suppose now that the extra stimulus has been found which arouses a satisfactory subst.i.tute response. The original stimulus, or the reaction-tendency aroused by it, still continuing, partic.i.p.ates in arousing the subst.i.tute response, playing the part of the originally ineffective stimulus in the conditioned reflex. Thus the original stimulus becomes strongly linked with the subst.i.tute response.

The process of reaching a subst.i.tute response thus includes three stages: (a) original response found unsatisfactory, (b) new stimulus found which gives a satisfactory subst.i.tute response, (c) attachment of the subst.i.tute response to the original stimulus.

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There are two main cases under the general head of subst.i.tute response. In one case, the subst.i.tute response is essentially an old response, not acquired during the process of subst.i.tution, but simply subst.i.tuted, as indicated just above, for the original response to the situation. This represents the common trial and error learning of animals. The second case is that where the subst.i.tute response has to be built up by combination of old responses into a higher unit.

C. Subst.i.tute Response, but not in Itself a New Response

I. Trial and error.

Our much-discussed instance of the _cat in the cage_ need not be described again, but may simply be ill.u.s.trated by a diagram.

[Ill.u.s.tration: Fig. 60.--How the cat learns the trick of escaping from the cage by unlatching the door. S is the situation of being shut up in a cage, and T is the tendency to get out. R1 is the primary response aroused by this tendency, which response meets with failure, not leading to the end-result of the tendency. Responses are then made to various particular stimuli about the cage, and one of these stimuli, the door-latch, X, gives the response R2 which leads to the end-result. Now the response R2 was in part aroused by T, and its pre-existing weak linkage with T is so strengthened by exercise that T, or we may say S, comes to give the correct response without hesitation.]

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2. Learning to balance on a bicycle.

When the beginner feels the bicycle tipping to the left, he naturally responds by leaning to the right, and even by turning the wheel to the right. Result unsatisfactory--strained position and further tipping to the left. As the bicyclist is about to fall, he saves himself by a response which he has previously learned in balancing on his feet; he extends his foot to the left, which amounts to a response to the ground on the left as a good base of support. Now let him sometime respond to the ground on his left by turning his wheel that way, and, to his surprise and gratification, he finds the tipping overcome, and his balance well maintained. The response of turning to the left, originally made to the ground on the left (but in part to the tipping), becomes so linked with the tipping as to be the prompt reaction whenever tipping is felt. The diagram of this process would be the same as for the preceding instance.

D. Subst.i.tute Response, the Response Being a Higher Motor Unit

1. The brake and clutch combination in driving an automobile.

This may serve as an instance of _simultaneous coordination_, since the two movements which are combined into a higher unit are executed simultaneously. The beginner in driving an automobile often has considerable trouble in learning to release the "clutch", which, operated by the left foot, ungears the car from the engine, and so permits the car to be stopped without stopping the engine. The foot brake, operated by the right foot, is comparatively easy to master, because the necessity for stopping the car is a perfectly clear and definite stimulus. Now, when the beginner gets a brake-stimulus, he responds promptly with his right foot, but neglects to employ his left foot on the clutch, because he has no effective clutch-stimulus; there is nothing {411} in the situation that reminds him of the clutch.

Result, engine stalled, ridicule for the driver. Next time, perhaps, he _thinks_ "clutch" when he gets the brake-stimulus, and this thought, being itself a clutch-stimulus, arouses the clutch-response simultaneously with the brake-response. After doing this a number of times, the driver no longer needs the thought of the clutch as a stimulus, for the left foot movement on the clutch has become effectively linked with the brake-stimulus, so that any occasion that arouses the brake-response simultaneously arouses the clutch response.