But there is a very ready and serious objection to this argument; for it may and does happen that an unsuccessful response is repeated several times during a single {393} trial, while the successful response is never made more than once in a single trial, since success brings the trial to a close; and thus, as a matter of fact, frequency often favors the unsuccessful response--which, nevertheless, loses out in compet.i.tion with the successful response.

Can the law of effect be interpreted as an instance of the sub-law of recency? The successful reaction always occurs at the end of a trial, and is the most recent reaction at the beginning of the next trial.

This recency might have considerable importance if the next trial began instantly (as in uns.p.a.ced learning), but can have no importance when so long as interval as a day is left between trials; for evidently the recency of twenty-four hours plus ten seconds is not effectively different from that of an even twenty-four hours. Recency, then, does not explain the law of effect.

Can it be explained as an instance of the sub-law of intensity? An animal, or man, who sees success coming as he is making the reaction that leads directly to success, throws himself unreservedly into this reaction, in contrast with his somewhat hesitant and exploratory behavior up to that time. The dammed-up energy of the reaction-tendency finds a complete outlet into the successful reaction, and therefore the successful reaction is more intensely exercised than the unsuccessful. This seems like a pretty good explanation, though perhaps not a complete explanation.

Limitations of the Law of Exercise

The law of exercise, with all its sub-laws, is certainly fundamental and universal; it is always in operation whenever anything is learned; and yet, just by itself, it goes only halfway towards accounting for learned reactions. For a reaction to be exercised, it must be _made_, and the law of exercise presupposes that it is made, and does not attempt to account for its being made in the first place.

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The law of exercise does not cover the formation of new linkages, but only the strengthening of linkages that are already working. It does not explain the attachment of a response to some other than its natural stimulus, nor the combination, of responses into a higher unit, nor the a.s.sociation of two facts so that one later recalls the other. We learn by doing, but how can we do anything new so as to start to learn? We learn by observing combinations of facts, but how in the first place do we combine the facts in our minds?

How, for example, can we learn to respond to the sight of the person by saying his name? Evidently, by exercising this linkage of stimulus and response. But how did we ever make a start in responding thus, since there is nothing about the person's looks to suggest his name?

The name came to us through the ear, and the face by way of the eye; and if we repeated the name, that was a response to the auditory stimulus and not to the visual. How has it come about, then, that we later respond to the visual stimulus by saying the name?

In short, the more seriously we take the law of exercise, the more we feel the need of a supplementary law to provide for the first making of a reaction that then, by virtue of exercise, is strengthened.

This is the problem that occupied the older writers on psychology when they dealt with "a.s.sociation"; and their solution of the problem was formulated in the famous "laws of a.s.sociation". The laws of a.s.sociation were attempts to explain how facts got a.s.sociated, so that later one could recall another.

These laws have a long history. From Aristotle, the ancient Greek who first wrote books on psychology, there came down to modern times four laws of a.s.sociation. Facts become a.s.sociated, according to Aristotle, when they are {395} contiguous (or close together) in s.p.a.ce, or when they are contiguous in time, or when they resemble each other, or when they contrast with each other. The psychologists of the earlier modern period, in the eighteenth and first part of the nineteenth centuries, labored with very good success to reduce these four laws to one comprehensive law of a.s.sociation. Contiguity in s.p.a.ce and in time were combined into a law of a.s.sociation by _contiguity in experience_, since evidently mere physical contiguity between two objects could establish no a.s.sociation between them in any one's mind except as he experienced them together.

a.s.sociation by Similarity

Continuing their simplification of the laws of a.s.sociation, these older psychologists showed that resemblance and contrast belonged together, since to be similar things must have something in common, and to be contrasted also two things must have something in common.

You contrast north with south, a circle and a square, an automobile and a wheelbarrow; but no one thinks of contrasting north with a circle, south with an automobile, or a square and a wheelbarrow, though these pairs are more incongruous than the others. Things that are actually a.s.sociated as contrasting with each other have something in common; and therefore a.s.sociation by contrast could be included under a.s.sociation by similarity. Thus the four laws had been reduced to two, a.s.sociation by contiguity and a.s.sociation by similarity.

The final step in this reduction was to show that a.s.sociation by similarity was a special case of a.s.sociation by contiguity. To be similar, two things must have something in common, and this common part, being contiguous with the remainder of each of the two things, establishes an indirect contiguity between the two things, a {396} sort of contiguity bridge between them. One thing has the parts or characteristics, A B X Y, and the similar thing has the parts or characteristics, C D X Y; and thus X Y, when seen in the second thing, call up A B, with which they are contiguous in the first thing.

A stranger reminds me of my friend because something in the stranger's face or manner has been met with before in my friend; it has been contiguous with my friend, and recalls him by virtue of this contiguity. The stranger, as a whole individual, has never been contiguous with my friend, but some characteristic of the stranger has been thus contiguous. In a.s.sociation by similarity, it is not the whole present object that arouses recall of the similar object, but some _part_ of the present object. This kind of a.s.sociation is important in thinking, since it brings together facts from different past experiences, and thus a.s.sembles data that may be applied to a new problem. If every new object or situation could only be taken as a whole, it could not remind me of anything previously met; and I should be like an inexperienced child in the presence of each new problem; but, taken part by part, the novel situation has been met with before, and can be handled in the light of past experience.

Exactly what there is in common between two similar faces or other objects cannot always be clearly made out; but the common characteristic is there, even if not consciously isolated, and acts as an effective stimulus to recall.

a.s.sociation by Contiguity

This reduction of all the laws of a.s.sociation to one great law was no mean achievement; and the law of a.s.sociation by contiguity in experience holds good. If one thing recalls another to your mind, you can be sure that the two {397} have been contiguous in your experience, either as wholes or piecemeal. For two things to become a.s.sociated, they must be experienced together.

Yes, the law holds good, when thus stated--but notice that the statement is virtually negative. It says, in effect, that two things do _not_ become a.s.sociated _unless_ they are contiguous in experience.

If it were turned about to read that two things do become a.s.sociated if they are contiguous in experience, it would no longer be a true law, for the exceptions would then be extremely numerous.

The memory and testimony experiments have brought many exceptions to light. Show a person twenty pictures in a row, and let him examine each one in turn so closely that he can later recognize every one of them; and still he will not have the adjacent pictures so a.s.sociated that each one can call up the next in order. To accomplish his last task, he has to observe the order specifically; it is not enough that he simply experiences pictures together. Or, again, read to a person twenty pairs of words, asking him to notice the pairs so that later he can respond by the second word of any pair when the first word is given him; and read the list through three or four times, so that he shall be able to make almost a perfect score in the expected test; still he will have formed few a.s.sociations between the contiguous pairs, and will make a very low score if you ask him to recite the pairs in order. Many similar experiments have yielded the same general result--contiguity in experience and still no a.s.sociation.

The law of a.s.sociation by contiguity is unsatisfactory from a modern standpoint because it treats only of the stimulus, and says nothing about the response. It states, quite truly, that stimuli must be contiguous in order that an a.s.sociation between them may be formed, but it neglects to state that the a.s.sociation, being something in us, must {398} be formed by our reaction to the stimuli. It is especially necessary to consider the response because, as we have just seen, the response is not always made and the a.s.sociation, therefore, not always formed. Only if the stimuli are contiguous, can the a.s.sociating response be aroused, but they do not infallibly arouse it even if they are contiguous.

The law of contiguity is incomplete, also, because it is not applicable to the a.s.sociation of two motor acts into a coordinated higher unit, or of the combination of two primary emotions into a higher emotional unit.

In a word, the time-honored law of a.s.sociation is no longer satisfactory because it does not fit into a stimulus-response psychology. It comes down from a time when the motor side of mental performances was largely overlooked by psychology, and when the individual was pictured as being pa.s.sively "impressed" with the combinations of facts that were presented to his senses.

The Law of Combination

What we need, then, as an improvement on the old law of a.s.sociation by contiguity, and as a supplement to the law of exercise, is some law governing the response to two or more contiguous stimuli. Now we already have such a law, which we put to some use in studying attention, [Footnote: See pp. 268-264.] and called the law of "combination", or of "unitary response to a plurality of stimuli". We had better fetch that law out again and put it in good repair, and see whether it is adequate for the job that we now have on hand. In a very general, abstract form, the law of combination read that "two or more stimuli may arouse a single joint response". Let us add a single word, which had not risen above the horizon when we formulated the law before, and say that {399} _two or more contiguous stimuli may arouse a single joint response_.

That seems very little to say; can we possibly go far with so simple a statement? Well, let us see. In saying that two or more stimuli arouse a single response, we imply that _there is already some rudimentary linkage between each stimulus and their common response, and that this linkage is used in arousing the response_. Now bring in our trusty law of exercise, and we see that the use, or exercise, of such a linkage may strengthen it to such an extent that, _later, a single one of the stimuli may arouse the response which was originally aroused by the whole collection of stimuli_.

Does that promise any better? Probably it requires further discussion and exemplification before its value can be appreciated. Let us, then, first discuss it a bit, and then apply it to the explanation of the chief varieties of learned reaction that have come to our attention.

The law of combination attempts to show how it comes about that a stimulus, originally unable to arouse a certain response, acquires the power of arousing it; and the law states that this occurs only when the originally ineffective stimulus is combined with others which can and do arouse the response. The ineffective stimulus, being one of a combination of stimuli which collectively arouse the response, partic.i.p.ates to some slight degree in arousing that response and may thus become effectively linked with the response.

Notice an a.s.sumption underlying the law of combination. Evidently a stimulus could not take part in arousing a response unless there were some pre-existing linkage between it and the response. This linkage may however be extremely loose and feeble, and wholly incapable by itself of arousing the response. The a.s.sumption of pre-existing loose linkage between almost any stimulus and almost any response is justified by the facts of playful behavior and trial and error {400} behavior. In addition to the close reflex connections provided in the native const.i.tution, and in addition also to the close connections formed in previous training, there are at any time, and especially in childhood and youth, a vast number of loose connections. These are too weak to operate singly, until they have cooperated in producing a response, and thus been individually strengthened, after which they may be able singly to produce the response.

The law of combination, then, as applied to learning, includes four points:

(a) A collection of stimuli may work together and arouse a single response.

(b) This is possible because of pre-existing loose linkage between the separate stimuli and the response.

(c) When any stimulus, working together with others, helps to arouse a response, its linkage with that response is strengthened by exercise.

(d) The linkage may be sufficiently strengthened so that a single stimulus can arouse the response without help from the other stimuli that were originally necessary.

Having now abundantly stated and reiterated the law of combination in the abstract, let us turn to concrete instances of learned reactions, and see how the law takes care of them. We have already cla.s.sified a large share of all the concrete instances under a few main heads, as subst.i.tute stimulus, subst.i.tute response, combination (or a.s.sociation) of stimuli, and combination of responses. We shall presently find it possible to reduce these four cla.s.ses to two, since the a.s.sociation of two objects, by virtue of which one of them later recalls the other, is a rather complicated case of subst.i.tute stimulus, while the combination of movements into a higher unit is a complicated case of subst.i.tute response.

[Footnote: To distinguish between "subst.i.tute stimulus" and "subst.i.tute response" is, in strict logic, like distinguishing between "inside out" and "outside in." Whenever there is a subst.i.tute stimulus there is also a subst.i.tute response, of course, since this stimulus, in being subst.i.tuted for another, gets that other's response in place of its own original response; and in the same way, you can always find subst.i.tute stimulus in any instance of subst.i.tute response; for, in being subst.i.tuted for another, a response gets that other's stimulus in place of its own original stimulus. For all that, the distinction between the two main cases of learning is of some importance, since sometimes the changed stimulus, and sometimes the changed response, is the interesting fact.]

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I. SUBSt.i.tUTE STIMULUS EXPLAINED BY THE LAW OF COMBINATION

Here the response, without being itself essentially changed, becomes attached to a new stimulus. We distinguish two cases under the general head of subst.i.tute stimulus. In the one case, the subst.i.tute stimulus was originally extraneous, and unnecessary for arousing the response, while in the other case it was originally necessary as part of a team of stimuli that aroused the response.

A. Subst.i.tute Stimulus Originally Unnecessary for Arousing the Response

1. Conditioned reflex.

This is the very simplest case belonging under the law of combination.

The dog that responded to the bell by a flow of saliva, after the bell plus a tasting substance had acted together on him time after time, is the typical instance; and another good instance is that of the little child who was "taught" to shrink from a rabbit by the sounding of a harsh noise along with the showing of the rabbit. [Footnote: See p.

303.] The explanation of all instances of conditioned reflex is the same. We have an effective stimulus acting, i.e., a stimulus strongly linked with the response; and we also have acting an ineffective stimulus, which gets drawn into the same reaction. The effective stimulus determines what response shall be made, and the other stimulus finds an outlet {402} into that response, being, as it seems, attracted towards the activated response, sucked into it. The weak linkage from the ineffective stimulus to the response, being thus used and strengthened, later enables this stimulus to arouse the response single-handed.

This sort of thing is best presented in a diagram. A full line in the diagram denotes a linkage strong enough to work alone, while a dotted line denotes a weak linkage. Letters stand for stimuli and responses.

In the diagram for conditioned reflex, A is the original effective stimulus (the rasping noise in the instance of the child and the rabbit), and B is the ineffective stimulus (the sight of the rabbit).

R is the shrinking response, linked strongly to the stimulus A and only weakly to the stimulus B, which has several other linkages fully as good as the linkage B-R. But A arouses the response R; and R, being thus activated, draws on B and brings the linkage B-R into use. After this has occurred a number of times, the linkage B-R has been so strengthened by repeated exercise that it can operate alone, so that the rabbit brings the shrinking response even in the absence of A, the noise.