Introduction. — Psychological tests of one kind or another have been in use since the founding of psychology. During the early history of psychology, tests were developed largely around sensory reactions. Fairly serviceable tests of keenness of vision, auditory acuity and color defects have been in use for more than fifty years. Sometime later methods of testing accuracy of motor coordination, speed of reacting to simple and complex situations appeared. Until the last two decades such tests were incorporated in the general treatment of psychology. These tests were looked upon as a part of the routine of the laboratory and no particular use was made of them except in the testing of railway and marine engineers. Within the past twenty years there has grown up a veritable school of testers which has ab- stracted the sensory methods from psychology and added a very much larger number of special tests. Since the time of Binet's early work, tests have gradually taken on a broader character. They have had to do with general abilities, "intelligence level" correlated with age and with occupations, rather than with the special senses. The field of testing is now extensive and even though the value of the results obtained from the various methods is not yet agreed upon, it is generally admitted that this work is in line with common-sense and has wide possibilities of still further extension. In general we may consider the tests under three headings: (1) general behavior tests for determining whether the individual possesses the various functions and the degree of plasticity (capability of forming new habits) demanded by society (so-called intelligence tests); (2) tests of special ability, and (3) research and statistical work in tests.
A good many psychologists are inclined, or were inclined in the beginning, to look upon tests as a development of a purely practical side of psychology, and hence asserted that they be- longed wholly to applied psychology. But by degrees this differ- ence between "pure" and' "applied" science has given way in psychology as it has in other fields. Now we look upon tests as we look upon any other group of methods in psychology. When the psychologist has special need of making them he either uses 44 PSYCHOLOGY a test already available or else goes about in a^systematic way the development of a test to suit his needs. He does this, or he should do this, in the same spirit that he would carry out other psycho- logical investigations. On the whole though this distinction is valid, viz., that psychological experimentation is carried out usu- ally without any reference to the immediate usability or applica- bility of the results, whereas the tests are used in practical situations and are (or ought to be) scientifically developed in the laboratory in order to meet practical situations.
The tests so far developed have had most to do with the language behavior of individuals and depend largely upon the individual's ability to speak; that is. they have concerned them- selves with the ease and complexity of the language response to social and other environmental settings. This is, of course, un- fortunate since we have many individuals who are deprived of speech altogether and many others with defective speech (aphasics and bad stammerers, for example), and still others who speak only the most difficult foreign languages. The ability of such individuals to do certain things with their hands, to form certain habits with the remaining musculature of their bodies, has not been disturbed. To meet such cases, and indeed to serve many other purposes as well, very much greater em- phasis should be laid upon tests of explicit and overt types of behavior where language is not necessary.2 Owing to the re- markable but widespread notion that language behavior has some peculiarly great significance, the development of perform- ance tests has been seriously handicapped. We can give only a brief characterization of the various types of tests here.
1. Tests to Determine the General Level of Behavior.
The validity of general behavior tests depends upon the fact that in individuals of approximately the same age and from the same general environment, certain systems of common activi- ties are developed. A^ has been brought out before, this expected or demanded level of activity is a purely conventional one. Nevertheless, every individual must be possessed of a certain minimal set of assets and activities, such as speed in forming 2 Some of the recent army tests have met this difficulty.
PSYCHOLOGICAL METHODS 45 habits, number of habits and a certain level of language attain- ment; of certain methods of attack upon problems and conven- tional modes of reacting to parents, teachers and companions. If the individual is lacking in any of these requirements, a prop- erly devised test should bring the matter out. Certain tests have been developed which bring out the completeness or incom- pleteness of such accomplishment with respect to age. We can, for example, give an individual of eight years all of the tests from six to nine years. It he passes all up to and including the eighth year, we say that his attainments are normal. If his attainments age is near that of a six-year-old child, we say that the individual is two years retarded. The mere fact that the individual may be two years retarded calls for special considera- tion of his case. Is he two years retarded because he has been ill and has not been able to go to school to the same extent as other children of his age? Has he been in a region where he was not able to go to school? Is there any particular psychosis of a permanent or temporary character which has been instrumental in producing retardation? Or has the youth constitutional de- fects which make it impossible for him to put on the habits required of the other children in his group? The special con- sideration of the retarded child thus requires the cooperation of a psychologist, a psychiatrist and oftentimes of a surgeon. Serious damage is often done to individuals who are passed upon by a physician alone or by a psychologist alone.
The scales or special tests used in this practical way are those of Binet-Simon with their various modifications at the hands of Terman, Yerkes, Goddard and others, and the performance tests of Healy, Pintner and many others. The various special tests described below may also be utilized to determine the general be- havior level of individuals. By the use of special tests in arith- metic, vocabulary, speed and rapidity of habit formation, we arrive at a much more just estimate of the individual's capabil- ities than by any of the tests for general behavior. Indeed, few of the modifications of the Binet-Simon and other general testing methods are serviceable beyond the 15th year. In estimating an adult's attainments we usually have to employ many special tests.
46 PSYCHOLOGY 2. Tests of Special Ability. — On account of various practical demands upon the psychologist both in the realm of the evalua- tion of attainment in schools and in the economic world, a num- ber of tests too numerous for special mention have grown up for the determination of special abilities. Tests have already been devised for determining the range of general information of an individual, information along a particular line, his mathe- matical ability, his vocabulary, English, handwriting, musical ability, ingenuity, the possibility of his attaining success in the fields of railway engineering, telephony, stenography, music and aviation. These special ability tests are sometimes used jointly in abbreviated form for running applicants through who are desirous of entering certain vocations. The tests are gradually becoming* wider in their scope so as to include personality fac- tors, for example, whether an individual is arrogant, proud, neat, whether he is friendly, or emotionally unstable. It has indeed been suggested that the psychiatrists might assist the psycholo gists in determining whether a candidate for the more important positions has the proper characteristics and temperament to make him desirable. In connection with this it may be said that an individual's characteristics are dependent to a large extent upon the various conflicts and stresses and strains against which he has had to contend from infancy through adolescence to his present age. Some further discussion of this is given on page 415.
3. Research and Statistical Work in Tests.— So far in our discussion- of tests we have assumed the existence of more or less adequate tests for a given purpose. Such tests now at hand for practical use have been developed by means of actual .reeearch work. Suppose, for example, we have to develop a test for determining an individual's qualifications for filling a posi- tion in stenography. We first set down the various character- istics and attainments we desire such an individual to have. We then go into any large stenographic office and still further in- crease our knowledge concerning the speed a successful individual should have in taking dictation, speed in typewriting from writ- ten material and copying from stenographic notes, length of time it takes the best individuals to make copies of letters, abilitv to PSYCHOLOGICAL METHODS 47 spell, to write unusual words, to file letters and to find letters in a file. On the basis of this wider knowledge we construct a series of performance tests which take, say, half an hour for any stenographer to go through. We may find that our first test is entirely too complicated and that only three or four of the best individuals in a large typewriting office can pass it. But we are just as likely, on the other hand, to make a test which is too easy, so easy indeed that even the poorest members of the group can pass it. We then work at the method until the average good stenographer can pass the test. Naturally the test must be constructed with reference to the field of general stenographic work. This test would not be suitable for accountants, for news- paper reporters or for any other vocational field. Such work is being done constantly by many business houses in consultation with psychologists. Indeed, many of the larger business houses now employ psychological experts for devising such tests. The construction of the test is a research problem. The use of the test can possibly be left to individuals who are not psychologists, but who may have received special instructions in its use.
A slightly different task it at hand when we have to ask the question: What are the general factors which enter into the make-up of a successful lawyer, statesman, newspaper corre- spondent, or aviator. We may say in, advance that no very ser- viceable correlations throwing light upon such questions have yet been obtained. To make the problem specific we may take up the study of the make-up of a successful aviator: What factors in the previous life of the aviator make for success in flying? Has the amount and kind of academic education anything to do with it? The stratum of society from which he comes, age, pre- vious occupation and salary obtained in it, marriage, and athletic attainments? To answer the question the necessary data are obtained from successful and unsuccessful pilots. The material so obtained is then subjected to statistical treatment and the co-efficients of correlation obtained.3 3 For method see Thorndike's Mental Measurements. For the extent to which such correlations have been worked out see Thorndike's article Science, 1919.
CHAPTER III THE RECEPTORS AND THEIR STIMULI Introduction. — As has already been pointed out, the under- standing of the nature of human response depends to a large extent upon a knowledge of the various types of stimuli which affect man; of the places where such stimuli must be applied in order to produce appropriate action; and of the various physical and physiological factors which must be taken into account in the control of both the organism and the stimulus. To make this concrete we need only to mention the fact that if the skin of cer-. tain animals is stimulated by light of high intensity an overt response will be produced. In man, light, neglecting its heat value, must fall upon, a certain part of the eye if action is to be produced. Furthermore, light necessary to produce an overt response in man must have a wave length not less than 397/x/x (violet) and not greater than 760^ (red). To bring these fac- tors out, we must to a certain extent "dissect" our human being and find the parts which are sensitive to stimulation (bodily areas which each sense organ comprises) and the adequate stimuli which, when applied upon these sense organ areas, will produce action. It must be borne in mind that this procedure is some- what artificial and like the one the physiologist uses when he studies the heart action, respiration, etc., to the exclusion of the other bodily functions. In later chapters, however, we will put the organisms together, as it were, and study our creation from the standpoint of its reactions as a whole. We must never lose sight of the fact that when man reacts to even the most minute sensory stimulus, the whole body cooperates in the reaction, even if he only raises a finger or says the word ' ' red. ' ' A General Neuro-Muscular Consideration. — We shall find in Chapter V that in every simple reflex act, such as the with- drawal of the hand from a hot object, there is involved on the structural side a receptor, or sense-organ structure, a set of neural conductors and an effector (muscle or gland). When a sense 48 THE RECEPTORS AND THEIR STIMULI 49 structure, like the eye, ear or nose, is played upon by a stimulus, a chemical process of some kind is started which releases a neural impulse in the system of conductors. This neural impulse passes through the conductors, finally reaching the muscle or gland. Under the action of this impulse, the muscle shortens or the gland begins to secrete. The animal thus moves or acts. In order to have these various mechanisms clearly before us, we shall have to study (1) the sense organ side of man: the eye, the ear, the senses of touch, olfaction, warmth, cold, pain, the organic and the kinaBSthetic; (2) the neural or conducting mechanism, i.e., the peripheral and central nervous systems (and the sym- pathetic nervous system); (3) the motor and glandular systems — the effectors, consisting of the striped muscles which are under the control of the peripheral and central nervous systems, and the unstriped muscles and glands which are usually under the control of the sympathetic. The student should formulate his problem somewhat as follows: * ' ( 1 ) What extra-organic and intra-organic stimuli will cause my subject, man, to act; how can I arrange simple and complex situations which will cause him to act in harmony with environmental demands? (2) From my general reading it would appear that the function of the stimulus is to arouse a neural impulse. I want to know for both practical and theoretical reasons what the course of this neural impulse is, i.e., how it finds a way to the muscle, because if there happens to be a defect, either anatomical or functional in this chain of conductors, I know that any stimulus I may apply will not lead to the usual reaction. (3) In order to understand what can be done with man in the way of establishing integrated sys~ terns of response, I must have at least an elementary knowledge of the ways in which muscles, tendons and joints function: and know something about the kinds of glands he has, and the influence of these glands upon the muscles." The student who has had no physiology will find it profitable to read straight through the three chapters on the sense organs, the conductors, and the muscles and glands, ani then turn back and study in detail the chapters in the order in which they appear. In our study of the sense organs which immediately follows, we shall 4 50 PSYCHOLOGY Sp- Sr-— have to neglect many points of interest. £)nly the common and more every -day phenomena of sensory physiology are treated here. ^ I. SENSE ORGANS IN THE SKIN (CUTANEOUS) AND THEIR ADEQUATE STIMULI.
Area. — The whole surface of the skin, including the red por- tion of the lips, the conjunctiva and cornea of the eye, the mucous membrane lining the mouth and other external openings of the body, must be looked upon as the area where cu- taneous stimuli may be effec- tively applied. Fig. 6 shows a cross section of skin of the body with the epidermis, or outer layer of the surface, removed.
If we investigate this area by either the condition- ed reflex method or by the verbal report method (page 38), we shall find that in the skin we are really deal- ing with four distinct sense organs, each with its proper group of stimuli. They are (1) the cold sense, (2) the Fio. B.-Cross-section of skin, with epidermis Warm Sense, (3) the pressure or outer layer removed (after Ruffini). At, cross- sense and (4-} thp rrnin QPTIQP section of small artery; cM, Meissner corpuscles; >• ' me Pam Sense.
cP, transverse section of Pacinian corpuscle; Sp', 1 anr? 9 arp Irnrvom nr\\ papillary layer of the skin; Sr, reticular layer of em.u. ^ die I\.IHJW.LL CUi- ?te«^^^l^Sa;S^iSS&BM; Actively as the temperature ' sense.
1 and 2. The Temperature Sense.— The adequate stimuli for these senses are, from the standpoint of physics, heat radiation. From the practical standpoint, they are objects: metal, wood, fluids and gases (air), being the most common examples. To ,nrl THE RECEPTORS AND THEIR STIMULI 51 initiate activity it is not necessary to bring such objects into direct contact with the skin. In general in order to affect the cold sense, their temperature must be lower than the so-called physiological zero, approximately 30° C. The physiological zero is not fixed, but depends upon the state of adaptation of the sense organ. If the temperature of the objects is above this point, the warm sense is called into function. The end organs of tem- perature can also be stimulated from within by organic changes which occur in fevers, in extreme emotions, either through con- stricture of the blood-vessels (cold) or by dilatation (warmth). They may also be stimulated mechanically by the action of sub- stances like mustard, pepper, alcohol or menthol, by an electrical current and possibly even by mechanical stimulation — slight tapping, puncturing with a needle, etc. Extremes of tempera- ture tend to destroy the tissue, and hence objects of excessively high temperature stimulate both the warm sense and the pain sense. The essential factor in providing a temperature stimulus is the bringing about of thermal changes in the skin. Unless the temperature of any part of the skin can be changed, fairly rap- idly at that, there is no response. This can be illustrated by the old example of immersing the frog and then raising the tem- perature very gradually. The death of the frog occurs before a temperature (or pain) response is obtained.
Punctiform. Type of Stimulation. — In making a systematic and detailed investigation of these senses, one usually marks off on the skin a small, well-defined area and goes over it with a hollow point of metal which can be kept at a constant tempera- ture by passing through it a fluid — water for warmth and moder- ate degrees of cold, alcohol or other anti-freezing fluids if low temperatures are to be used. For ordinary work the point of metal should be kept at about 12° to 15° C. when the cold sense is being investigated, and 37° to 40° C. when working with the warm sense. If the skin is gone over in a punctiform way, it is found that characteristic responses can be obtained only at cer- tain definite circumscribed spots or points (!/2 mm- or less ^n area). Moreover, points which respond to the cold metal point are distinct from those which respond to the warm. Appar- 52 PSYCHOLOGY 52 PSYCHOLOGY ently they are permanent: that is, the sjpots are probably situ- ated immediately above the true sense-organ structure lying within the skin. In general it is found that those regions which are most responsive to pressure stimuli as, e.g., the hands and finger tips, are less responsive to temperature. Parts which are usually covered with clothing are more responsive to temperature than those which are left uncovered, partly because of lack of exposure to changes, but also because they are more generously supplied with temperature organs. The face is exceedingly sensitive, although in most countries it is left uncovered. It is found to be richly supplied with sensory structures. The threshold of stimulation of these spots varies widely.1 Stimula- tion of certain warm spots will produce response when the tem- perature of the object is only slightly above the physiological zero, while the more resistant are not stimulated except by tem- peratures lying around 40° C. The cold spots show equal vari- ation in the intensity of the threshold stimulus. The number of spots sensitive to these forms of stimuli in any given square centimeter differs widely on the different parts of the body. In general the cold spots are much more numerous than the warm 1 There are two kinds of thresholds. Liminal thresholds, abbreviated R. L.: by this is meant merely that any stimulus in any sense field can be made so weak that the work it does upon the sense organ is not sufficient to produce either an explicit or an implicit response. The state of adapta- tion or the amount of work the sense organ has just done may affect the magnitude of the stimulus necessary to produce a response. The differential threshold (D. L.) always involves two stimuli: a subject may react to a white light of a given photometric value. Suppose we introduce a second white light. By how much must we increase (or decrease) the intensity of this second light in order to have at hand the condition for the subject to react in one way to the first light, and in another way to the second light? Reactions to such stimuli are called in the text differential reactions or responses. There is a separate division of psychology which deals almost exclusively with such relations of stimuli. It is called quantitative psy- chology. The originators of this type of study were Weber and Fechner. Their studies have been incorporated into- so-called laws — the Weber law and the Fechner law, or the Weber-Fechner law. On account of the very narrow application of quantitative.psychology and by reason of the tech- nical difficulties in the way of its study, it is neglected in this text, although the subject matter belongs to objective psychology.
THE RECEPTORS AND THEIR STIMULI 53 spots. On the average the proportion is about 13 cold spots to 2 warm spots. In the matter of the distribution of these spots, attention is called to the fact that the conjunctiva of the eye and the external mucoufc membrane of the genital organs are insen- sitive to warmth but sensitive to cold.
Areal Stimulation. — Punctiform stimulation such as we have just described rarely occurs in the daily life of man. It is the cold wind striking all of the exposed surfaces of the body which leads him to put on his overcoat or to go to the coal yards and lay in his winter supply of fuel. It is the warm rays of the sun that make him doff his winter garments and eagerly hunt rail- way time-tables for summer resorts. Areal stimulation may, apart from daily life, be investigated in the laboratory. A thermal stimulation distributed over a large area of the skin is reacted to more strongly than if the same temperature is applied to a smaller area. A temperature which will just not produce a reflex withdrawal when the finger alone is dipped into a fluid will produce a withdrawal movement if the whole hand or arm is immersed. Most of us have many times tested our bath water with the finger tips, jumping in only to bounce out again when the entire leg or body is suddenly immersed. Objects with different heat conductivities affect markedly the reactions of the subject. Water at 25 °C. is a stronger cold stimulus than oil at the same temperature, but less strong than mercury. In addi- tion to the heat-conducting properties, the action (as seen in R. L. and D. L.) induced by the temperature of an object depends to some extent upon the smoothness or roughness of its surface.