How may we explain the late distinction of right and left as compared with up and down? At least four theories may be advanced: (1) Something depends on the frequency with which children have occasion to make the respective distinctions. (2) It may be explained on the supposition that kinæsthetic sensations are more prominently involved in distinctions of up and down than in distinctions of right and left. It is certainly true that, in distinguishing the two sides of a thing, less bodily movement is ordinarily required than in distinctions of its upper and lower aspects. The former demands only a shift of the eyes, the latter often requires an upward or downward movement of the head. (3) It may be due to the fact that the appearance of an object is more affected by differences in vertical orientation than by those of horizontal orientation. We see an object now from one side, now from the other, and the two aspects easily blend, while the two aspects corresponding to above and below are not viewed in such rapid succession and so remain much more distinct from one another in the child’s mind. Or, (4), the difference may be mainly a matter of language. The child undoubtedly hears the words up and down much oftener than right and left, and thus learns their meaning earlier. Horizontal distinctions are commonly made in such terms as this side and that side, or merely by pointing, while in the case of vertical distinctions the words up and down are used constantly. This last explanation is a very plausible one, but it is very probable that other factors are also involved.
The distinction between right and left has a certain inherent and more or less mysterious difficulty. To convince one’s self of this it is only necessary to try a little experiment on the first fifty persons one chances to meet. The experiment is as follows. Say: “I am going to ask you a question and I want you to answer it as quickly as you can.” Then ask: “Which is your right hand?” About forty persons out of fifty will answer correctly without a second’s hesitation, several will require two or three seconds to respond, while a few, possibly four or five per cent, will grow confused and perhaps be unable to respond for five or ten seconds. Some very intelligent adults cannot possibly tell which is the right or left hand without first searching for a scar or some other distinguishing mark which is known to be on a particular hand. Others resort to incipient movements of writing, and since, of course, every one knows which hand he writes with, the writing movements automatically initiated give the desired clue. One bright little girl of 8 years responded by trying to wink first one eye and then the other. Asked why she did this, she said she knew she could wink her left eye, but not her right! One who is resourceful enough to adopt such an ingenious method is surely not less intelligent than the one who is able to respond by a direct instead of an intermediate association.
It seems that normal people never encounter a corresponding difficulty in distinguishing up and down. The writer has questioned several hundred without finding a single instance, whereas a great many have to employ some intermediate association in order to distinguish right and left. It is the “p’s and q’s” that children must be told to mind; not the “p’s and b’s.” The former is a horizontal, the latter a vertical distinction.
Considering the difficulty which normal adults sometimes have in distinguishing right and left, is it fair to use this test as a measure of intelligence? We may answer in the affirmative. It is fair because normal adults, notwithstanding momentary uncertainty, are invariably able to make the distinction, if not by direct association, then by an intermediate one. We overlook the momentary confusion and regard only the correctness of the response. Subjects who are below middle-grade imbecile, however long they have lived, seldom pass the test.
This test found a place in year VI of Binet’s 1908 scale, but was shifted to year VII in the 1911 revision. The Stanford statistics, and all other available data, with the exception of Bobertag’s, justify its retention in year VI. It is possible that the children of different nations do not have equal opportunity and stimulus for learning the distinction between right and left, but the data show that as far as American and English children are concerned we have a right to expect this knowledge in children of 6 years.
VI, 2. Finding omissions in pictures
Procedure. Show the pictures to the child one at a time in the order in which they are lettered, a, b, c, d. When the first picture is shown (that with the eye lacking), say: “There is something wrong with this face. It is not all there. Part of it is left out. Look carefully and tell me what part of the face is not there.” Often the child gives an irrelevant answer; as, “The feet are gone,” “The stomach is not there,” etc. These statements are true, but they do not satisfy the requirements of the test, so we say: “No; I am talking about the face. Look again and tell me what is left out of the face.” If the correct response does not follow, we point to the place where the eye should be and say: “See, the eye is gone.” When picture b is shown we say merely: “What is left out of this face?” Likewise with picture c. For picture d we say: “What is left out of this picture?” No help of any kind is given unless (if necessary) with the first picture. With the others we confine ourselves to the single question, and the answer should be given promptly, say within twenty to twenty-five seconds.
Scoring. Passed if the omission is correctly pointed out in three out of four of the pictures. Certain minor errors we may overlook, such as “eyes” instead of “eye” for the first picture; “nose and one ear” instead of merely “nose” for the third; “hands” instead of “arms” for the fourth, etc. Errors like the following, however, count as failure: “The other eye,” or “The other ear” for the first or third; “The ears” for the fourth, etc.
Remarks. The test is one of the two or three dozen forms of the so-called “completion test,” all of which have it in common that from the given parts of a whole the missing parts are to be found. The whole to be completed may be a word, a sentence, a story, a picture, a group of pictures, an object, or in fact almost anything. Sometimes all the parts of the whole are given and only the arrangement or order is to be found, as in the test with dissected sentences.
Further discussion of the completion test will be found in connection with [test 4, year XII]. For the present we will only observe that notwithstanding a certain similarity among the tests of this type, they do not all call into play the same mental processes. The factor most involved may be verbal language coherence, visual perception of form, the association of abstract ideas, etc. To pass Binet’s test with mutilated pictures requires, (1) that the parts of the picture be perceived as constituting a whole; and (2) that the idea of a human face or form be so easily and so clearly reproducible that it may act, even before it comes fully into consciousness, as a model or pattern, for the criticism of the picture shown. The younger the child, the less adequate, in this sense, is his perceptual familiarity with common objects. In standardizing a series of “absurd pictures,” the writer has found that normal children of 3 years often see nothing wrong in a picture which shows a cat with two legs or a hen with four legs. Such children would, of course, never mistake a cat for a hen. Their trouble lies in the inability to call up in clear form a “free idea” of a cat or a hen for comparison with the perceptual presentation offered by the picture. Middle-grade imbeciles of adult age have much the same difficulty as normal children of 4 years in recognizing mutilations or absurdities in pictures of familiar objects.