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{"created":"2022-01-31T15:19:33.861207+00:00","id":"lit28748","links":{},"metadata":{"alternative":"Studies from the Yale Psychological Laboratory","contributors":[{"name":"Scripture, Edward W.","role":"author"}],"detailsRefDisplay":"Studies from the Yale Psychological Laboratory 8: 1-20","fulltext":[{"file":"p0001.txt","language":"en","ocr_en":"A TEST OF SAFE COLOR VISION\nBY\nE. W. Scripture.\nThe problem that confronts the examiner of the color vision of applicants for positions on the railway and on shipboard has been frequently misunderstood. The usual test with colored wools aimed at picking out two classes of men with so-called green-blind and red-blind vision. The object of any test for color vision employed in these two services should be to pick out the men who can with absolute safety be trusted to recognize the signal colors. The two systems of testing are quite opposite ; the one picks out and excludes men conspicuously unsafe and lets all the others into the service, while the other picks out and passes only the absolutely safe ones and excludes all others. When human life may be endangered by a mistake, the only admissible test is the latter one. It is my opinion that one, and only one, test.of color vision should be used by examiners : namely, one that proves every person tested by it to be of safe or of unsafe color vision.\nPrinciples for a test of color vision.\nThe fundamental requirement for a test of color vision is that of reliability ; the test must with absolute certainty exclude all forms of color defect that would interfere with service on the railway and on shipboard, and must not exclude persons who do not possess such defects.\nThis requirement is not met by the wool test. In the first place there are many cases of rejection for color blindness which later examination proves to have been unjustified. There are also many cases of color blindness discovered after the person has passed the test ; these are regularly treated as cases of \u201c acquired\u201d color blindness without the certainty that they are not sometimes cases of overlooked color blindness.\nOn the other hand, railway and marine surgeons who use a test with colored glasses in addition to the wool test, constantly report the discovery of cases by the one form of test which have successfully passed the other one. This would indicate that neither the wool test nor the usual test with colored glasses is reliable.\nThe first principle to be adopted for a test is that of the closest possible resemblance to the actual conditions under which lights are to be\ni","page":1},{"file":"p0002.txt","language":"en","ocr_en":"2\nE. W. Scripture,\njudged. In practice a railway man or a pilot is required to decide for himself which of the lights he sees are red, green and white. An ideal test would consist of an immense number of such lights under all the variations of brightness, distance, fog, etc. Any concrete test should consist in the reduction of this ideal to a convenient form.\nThe usual wool test fails in respect to this principle. In practice the railway man or pilot is never required to put into a pile all the objects that resemble a certain sample.\nThe second principle is derived directly from the first one : the objects used in the test should resemble the objects in actual practice. Colored lights would conform to this principle.\nA third principle may likewise be deduced from the first one : the person tested should be required to name the objects. This is just what he does in thinking about the lights he sees when at work ; he decides that this one is \u201c red,\u201d that one is \u201c green,\u201d etc.\nThe judgment of the likeness or unlikeness of colored objects is an utterly different matter and involves a different form of mental activity. Great trouble and uncertainty arise in the wool test because it demands a different form of judgment from that to which the men have been accustomed.\nThe usual objection to having the colors named arises from the fact that such naming is inadmissible in the Holmgren test.\nA fourth principle may also be deduced from the first one : several colors should be presented simultaneously for coihparison. In practice the person sees several lights together ; he compares them and decides on their colors. The secret of the past success of the Holmgren test over the tests of the Donders form with colored glasses lies in its use of the principle of comparison. The ideal test would combine this principle with the other three in which the Holmgren test fails.\nThe color sense tester as first devised1 has undergone several changes. The principles on which it is based were first published2 in outline in 1899; the foregoing account summarizes them briefly. The present account of the first model is reproduced with some changes from an account in the Proceedings of the IV. International Congress of Psychology, Paris, 1900. The second model is here described for the first time.\nThe color sense tester (first model).\nIn general appearance the color sense tester resembles an ophthalmo-\n1\tScRirTURE, Some new apparatus, Stud. Yale Psych. Lab., 1895 III 103.\n2\tScripture, Color blindness and its tests, Proceedings of the N. Y. Railway Club, Nov. 16, 1899.","page":2},{"file":"p0003.txt","language":"en","ocr_en":"A test of safe color vision.\n3\nscope. On the side toward the person tested, Fig. i, there are three windows of glass 8m,n in diameter, numbered i, 2 and 3 respectively. The opposite side of the tester, Fig. 2, consists of a movable disk carrying twelve glasses of different colors. As this disk is turned by the finger of the operator the various colors appear behind the three windows.\nFic.. i.\tFig. 2.\nAt each movement of the disk the subject calls off the colors seen at the windows. Number 1 carries a very dark smoked glass ; all colors seen through it will be dark. Number 2 has no glass, showing all colors in full brightness. Number 3 carries a light smoked glass. There are thus thirty-six possible combinations of the colors. The twelve glasses are, however, reds, greens and grays.\nA suitable arrangement of tl>e colors gives direct simultaneous comparisons of reds, greens and grays of different shades. The well-known","page":3},{"file":"p0004.txt","language":"en","ocr_en":"4\nE. IV. Scripture,\nconfusion by color-defectives of dark gre\u00ebns with reds, greens with gray, etc., are exactly imitated, and the instrument gives a decisive test for color blindness. A peculiar advantage, however, lies in the fact that it presents reds, greens and grays simultaneously in a large number of different shades of intensity. The light of a green lantern, as it appears to a color defective at different distances, is simulated by the red behind the darker gray ; at the same time a white light [ is also changed. The color defective to whom weak green is the same as gray (white at a distance) is confused and thinks that the weakened green is gray (white) and the dark gray is green.\nThe actual test is performed in the following manner. The tester is held before a window or a white surface, but not in the bright sunlight, at about 5 meters from the person tested. The operator begins with any chance position of the glasses, and asks the person tested to tell the colors seen through the three glasses, numbers 1, 2 and 3. He answers, for example, \u201c number 1 is dark red ; number 2 is gray ; number 3 is green.\u201d The operator records from the back of the tester the letters indicating what glasses were actually used. Suppose he finds that A, D and G were opposite the glasses numbered 1, 2 and 3, he records: A,, dark red; D2, gray ; G3, green. The disk is then turned to some other position, the colors are again named, and the operator records the names used. For example, the result might be : \u201c number 1 is dark green ; number 2 is white; number 3 is red \u201d; and the record would read : G,, dark green ; J2, Avhite ; As, red. Still another record might give : J\u201e dark gray ; Aa, red; Ds, medium gray. Similar records are made for all combinations. Of course, the person tested knows nothing concerning the records made.\nThe records can be taken by anyone, and, on the supposition that the record has been honestly obtained and that the instrument has not been tampered with after leaving the central office, the comparison is likewise mechanical. There is none of the skillful manipulation required in the wool test and none of the uncertainty attaching to its results. The only instruction given to the subject is \u201c Name the colors \u201d; the results render the decision with mechanical certainty.\nThe requirements of simplicity and portability have, I hope, been successfully met ; at the same time the instrument is thoroughly scientific in its principles.\nThree colors at a time make a number agreeable to the subject ; more would probably distract him. It is a fact well established by experimental psychology that under ordinary circumstances the mind cannot well attend to more than five objects at a time ; the number 3 is within the limit.","page":4},{"file":"p0005.txt","language":"en","ocr_en":"A test of safe color vision.\nS'\nThe kind of comparison required is exactly the kind demanded in practice The pilot, for example, is never required to decide if one -color is \u201clike\u201d another, but to decide which colors are red, which green and which white. The Holmgren test requiring a judgment of \u201clikeness \u201d or \u201c unlikeness \u201d forces the subject to go through a difficult and complicated mental process. With the color sense tester the subject, seeing three colors at a time, passes judgment as to what colors they are.\nThe slide shown in Fig. 3 renders it possible to carry out tests quantitatively after the method proposed by Donders. The slide contains holes with the diameters of 1, 2, 3, 4, 5, 6, 7, Smm respectively. Using a standard source of illumination and placing the person tested at a given distance, the examiner can determine the smallest opening with which a certain color, say red, can be distinguished. If the smallest opening as determined for the average person be R mm and for the person tested rmm,\nr\nthe sensitiveness can be said to be indicated by S = \u2014. The other quan-\nK\ntitative test can likewise be readily carried out ; a standard opening, say imm is selected and the person tested is made to approach the instrument until he can distinguish the color. If D mm is the average distance found and dmm that for the person tested, his sensitiveness can be indicated\nCases of color defect of the central part of the eye only are generally due to the excessive use of tobacco, especially when combined with the abuse of alcohol. To detect these cases the slide (Fig. 3) is placed in\nFig. 3.\nwindow number 2 of the tester, and the person is required to call off the colors seen through the opening of imm or 2\u201d\"\u201c while the examiner shows them in rapid succession. The rapid succession is needed to allow no time for the person to turn his eye sidewise so that the colors fall outside the center.\nThe tester can be carried readily in the pocket, and can be used wherever a light of medium intensity is available.\nWhen portability is not desired, the tester can be used in front of a properly arranged lantern. The ordinary semaphore lantern may be readily adapted to the purpose as shown in Fig. 4 by putting a cap and a small support in front of the lens. I use a semaphore lantern contain-","page":5},{"file":"p0006.txt","language":"en","ocr_en":"6\nE. IV. Scripture,\ning a sixteen-candle power incandescent lamp and a sheet of white glass. The tester is simply laid in the small projecting arm in front of the glass. The examiner can see the letters marked on the edge of the tester. This form of the test is highly convenient for a permanent station, as it is always ready with the correct light.\nThese testers are now in use in several places. One examiner writes that \u201cthe men examined say that this test is more like the signals they\nare used to seeing every day on the road, and is therefore fairer than to ask them to pick out a lot of delicately tinted pieces of yarn.\u201d Yet this same examiner relates that he has by means of the tester caught a number of men who slip through the wool test.\nThere remains the question : Is this test alone sufficient for full protection of the traveling public? A proper test should be absolutely reliable. The employment of several tests indicates that none of them is reliable. I believe that the color sense tester is thoroughly scientific in its\nFig. 4.","page":6},{"file":"p0007.txt","language":"en","ocr_en":"A test of safe color vision.\n7\ncharacter and that it is reliable and decisive. Moreover, I have in my experience caught with it a number of men who had passed the wool test, and have never found one who passed the tester and yet showed any indication of color blindness in any way.\nInstructions.\nThe following instructions are issued for the use of the examiner :\nThe eyes should be examined separately ; a small blinder may, if desired, be hung over the eye not in use.\nHold the tester toward a bright surface (a window, the sky or the glass of a lantern) directly in front of the person to be examined, at a distance of five meters from his eye. The side with the three windows should be toward him. Ask him to call off the colors of these three windows in their order, beginning at the left window marked i ; thus, he is to say \u201cNumber i is such or such a color ; number 2 is such or such a color; number 3 is such or such a color.\u201d You, the examiner, are then to notice the letters under the colored circles behind the three windows and to note the results on the record blank in the proper spaces. Thus, if he answers \u201c Number 1 is red ; number 2 is gray ; number 3 is green,\u201d you look at the back of the tester and find, for example, that glass G is opposite number x, D opposite number 2 and A opposite number 3. On the record blank you find a line containing in three blank spaces numbered Gj, D\u201e, A3 and you write the answers in these places. While making the record you will have laid the tester down. You now turn the movable disc one or two or more notches either way; you hold the tester before the window and ask for answers as before. In this way you proceed until the record blank has been completely filled. A comparison of the answers with a list of the actual colors will at once reveal the defect if present. When color blindness is present, it is well to write the true colors in red ink in the same space with the answers of the person examined.\nOccasionally it occurs that the person examined has a central defect of the field of vision which affects his perception of the object directly looked at if it is small. To detect this defect, place under the central window of the tester, the slide having the small holes. Place the xmm or 2\"\"\u201d hole in the middle of the window. Ask him to call off the colors as you turn the movable disc with considerable rapidity. The rapidity is advised in order to hinder the person from forming an opinion by using a sjde portion of the eye.\nAt the bottom of the blank the decision should be recorded as to the good or defective color sense of the person examined. No attempt","page":7},{"file":"p0008.txt","language":"en","ocr_en":"8\nE. W. Scripture,\nshould be made to state whether an existing defect is due to \u201cred blindness\u201d or \u201c green blindness\u201d or \u201ccolor weakness,\u201d as such theoretical matters are still unsettled, the most common forms of color blindness being probably neither red nor green blindness. The question for you to decide is : Can this person distinguish and recognize with absolute certainty the lights used in practical service ? The foregoing test will give the answer and any further testing or experimenting is a personal matter with the examiner.\nRecord blank.\nExamination with E. W. Scripture\u2019s Color Sense Tester No.\nPlace...................................Date........\nName of Examiner....................................\nName of Person examined.............................\nAge........Residence................................\nRemarks.............................................\nLeft eye.\nRight eye.\nA>\tJ,\tGs\nB,\tk2\th3\nC>\tl2\t\\\nD,\ta2\tJs\nEl\tb2\tK,\nF 1\tC2\tl3\nG,\tD*\ta3\nH,\te2\tBa\nI,\tf2\tC3\n\tg2\tD3\nKi\th2\te3\nL,\tI,\tF3\nA,\tA \tG3\nB,\tK\th3\nc,\tl2\tI.\nD,\tA2\tJ3\nE,\tb2\tK3\nEl\tC2\tl3\ng,\tD2\ta3\nHl\t\tb3\nI,\t_F\"\tC3\nJl\tG,\tD3\nK,\th2.\te3\nL,\t\tF3\tI","page":8},{"file":"p0009.txt","language":"en","ocr_en":"A test of safe color vision.\n9\nThe examiner must answer the following questions by \u2018 \u2018 Yes \u201d or \u201c No. \u2019 \u2019 i Do the results of the tests with large openings indicate safe color\nvision for the left eye?....for the right eye ?......\n2. Does the test with the small opening indicate a central defect for the left eye ?.....for the right eye ?......\nThe color sense tester (second model).\nThe second model of the color sense tester differs from the first in providing for a much greater number of combinations of colors. The handle supports a brass frame holding a piece of white glass in front of which are ten circular holes. This provides ten windows of evenly dis-\ntributed white light. In addition to this part there is first a disc with ten windows of glass of the colors used for signaling. These colors are carefully matched with the signal colors and tested by the spectroscope ; the disc is lettered along its edge. Another disc of similar arrangement carries ten shades of glass from clear glass to the darkest smoke-glass that can be obtained. A number is placed on the edge opposite each glass. Two diaphragms are also provided. One has five holes of the full size of the windows so arranged that as the diaphragm is turned in front of the windows each window is at some time compared with every other window. The other diaphagm has five holes of imm diameter arranged in the same way.","page":9},{"file":"p0010.txt","language":"en","ocr_en":"IO\nE. IV. Scripture,\nThe lantern for this tester may be used with either a small incandescent electric lamp or an oil light. For permanent testing stations a semaphore lantern with an 8 c.p. incandescent lamp of the candle shape has been found convenient. The back window of the lamp serves for recording results when the room is darkened. In darkness the letters and numbers on the edges of the discs are read by lifting the tester from its support ; it can be lifted or replaced by a single movement of the hand. Usually it will be found sufficient to note only the mistakes of the person tested, recording the name given by him and the true name of the color. Practice and experience will soon enable the examiner to conduct the test efficiently with no other record than the final \u201c safe \u201d or \u201c unsafe.\u201d\nInstructions.\nThe instructions for making the test differ somewhat from those with the first model.\nThe examination should be made in a dark room. The eyes should be tested separately ; a small blinder may be hung over the eye not in use.\nPlace the lantern on a table at the height of the eyes of the person tested and at ten feet (three meters) from him. Place the tester in the catches on the front of the lantern.\nThree separate tests are to be made.\nFirst test.\nUse only the disc with the colored glasses and the diaphragm with five large holes.\nTell the person to call off promptly the colors he sees, beginning with the color farthest from all the others or with any one you may indicate by covering it a moment with the finger and proceeding around in the direction of the hands of a clock.\nNote down any mistakes that are made. Thus, if he calls yellow \u201cred,\u201d you should note down under the heading of Test I: Yellow called red. Confusions between yellow and white are not to be considered as mistakes, because the source of light is itself yellow, although ordinarily called white.\nTurn both disc and diaphragm irregularly and again call for the names. Note mistakes as before.\nRepeat about 10 times.\nA person who makes mistakes in this test can be at once declared of unsafe color vision without further testing.\nIn testing it is well to use as few words as possible. Thus, the instruction should be given : \u201c Name the colors in this order,\u201d etc. It is also","page":10},{"file":"p0011.txt","language":"en","ocr_en":"A test of safe color vision.\n11\nproper to demand, \u201c What is this color that I cover with my finger for a moment,\u201d but it is not proper to ask, \u201cIs this color red? \u201d and the like.\nSecond test.\nUse only the disc with the colors and the diaphragm with 5 small holes.\nThe test is conducted in the same way as the first test, except in requiring the answers with great rapidity.\nThe object of this test is to detect cases of color defect that are confined to the central spot of the eye. The naming must be done with sufficient rapidity to prevent the person from using the side portions of the eye.\nThird test. \u25a0\nPlace the disc with colors first on the axle, then on that the disc with smoke-glasses and finally the diaphragm with 5 large holes.\nThe test is conducted in the same manner as the first test except in turning irregularly all three parts of the tester.\nThe ten smoke-glasses give ten shades of each color, and the ten possible relative positions of the diaphragm disc to the color discsmultiply the number of combinations by ten. The ten possible positions of the color disc itself further multiply the result. There are thus 1,000 different combinations. It will be necessary to use only 15 or 20 of these, produced at random by the irregular movement of the parts in different directions, provided the person makes no mistakes. Confusions between dark green and blue and between white and yellow are not to be counted as mistakes.\nIf the subject makes mistakes or hesitates in his answers, a considerably larger number of combinations should be tried and the mistaken answers should be carefully recorded, the true color being written under the name given it.\nAny person who calls a white or a yellow by the names \u2018 \u2018 red \u2019 \u2019 or \u201c gr\u00ea\u00e8n, \u201d or a red by the names \u201cwhite,\u201d \u201cyellow\u201d or \u201cgreen,\u201d ora green by the names \u201cwhite,\u201d \u201cyellow\u201d or \u201cred,\u201d is to be classed as of unsafe color vision.\nGeneral suggestions.\nWhile the test is going on, never tell the person whether his answers are right or wrong. If deemed advisable, the mistakes can be told at the end of the test.\nIn putting on the color disc it is well to vary the side toward the lantern ; this varies the order of the colors.","page":11},{"file":"p0012.txt","language":"en","ocr_en":"12\tE. W. Scripture,\nThe following form of record is suggested :\nName of person examined.......................................\nAge Residence.................................................\nPrevious history..............................................\n(Note here anything that may have a bearing on color sense. )\nFor the left eye the color sense was found to be..............\n(The examiner must answer \u201c safe \u201d or \u201c not safe.\u201d)\nFor the right eye the color sense was found to be.............\n(The examiner must answer \u201c safe \u201d or \u201c not safe.\u201d )\nTest I. Mistakes made :\nTest II. Mistakes made :\nTest III. Mistakes make :\nPossible forms of color vision that may be met in testing.\nIt seems a well-established fact that most persons possess a color system in which any color can be considered as resulting from the union of three fundamental colors, red, green and blue. Such persons are called \u201ctrichromats.\u201d\nIf all trichomats possessed exactly the same vision of color, we could establish equations showing how much red, green and blue are required to produce any given color. It is a fact that, if we allow room for considerable variation, such equations can be established for a large portion of the trichromats. Such a group of persons might be said to possess a common \u201c type \u201d of color vision. By this we would not mean that the color vision was exactly alike in all cases but that they varied according","page":12},{"file":"p0013.txt","language":"en","ocr_en":"A test of safe color vision.\nr3\nto the usual laws of organic variation around a mean or average form of color vision. This type of color vision, which is that of the majority of human beings, is called \u201cnormal trichromasy.\u2019\u2019\nAs color vision is one of the properties of an organism, we may expect it to vary as other properties do. The fundamental principle of variation leads us to expect that among trichromats there will be individuals in whom the red, or the green, or the blue sensation is weaker than in the normal trichromats. Such individuals have been found ; they may be called \u201c color weak trichromats.\u201d\nI have had cases of this color weakness among my students. The first one I observed was absolutely perfect in passing the usual wool test but told me, after it was over, that when watching an approaching car carrying a red or a green light, he was unable to tell the color until it had approached within a block or two. When the wools were removed to a considerable distance away, he became completely confused and made judgments like a person in whom the green sensation was weak or lacking.\nThe cases are not so uncommon or so striking as would at first be supposed. Engineers have confessed\u2014generally regarding some friend\u2014 that the wool tests have been passed by men who could not distinguish the signal lights in a fog. Some years ago several letters appeared on the subject in the London \u201cTimes\u201d of which I quote a few.1 One engineer made the following statement : \u201cI have been on the railway for thirty years, and I can tell you the card tests and wool tests are not a bit of good. Why, sir, I had a mate that passed them all, but we had to pitch into another train over it. He couldn\u2019t tell a red from a green light at night in a bit of a fog.\u201d Another wrote : \u201c To me the colored skeins of the wool test are no test at all, for both reds and greens in all shades are unmistakable ; and although I have undergone this examination whenever an opportunity has presented itself, I have never tripped. Close at hand, reds and greens are to me as to other people ; at a distance, however, my sense of color, in regard to red especially, is all astray. Standing on the edge of a large field glowing with poppies, I see them up to about thirty or forty yards as other people see them ; but beyond that distance they gradually merge into a neutral tint and become lost. ... A distant red light over a chemist\u2019s door appears to be a dull yellow, and the same applies to a red railway signal.\u201d Another person writes, concerning his wife : \u201cThe red geraniums near my window she could see as well as I could ; but those a hundred yards off were lost in the green. She could choose and compare colored\n1 Eldridge-Green, Color Blindness, 216, 217, 227, London 1891.","page":13},{"file":"p0014.txt","language":"en","ocr_en":"14\nE. W. Scripture,\nsilks or worsteds, and could paint well, and was a remarkable good colorist. \u2019 \u2019 Such persons can be considered as cases of color-weakness.\nIn another type of color vision, known as \u201cabnormal trichromasy \u201d the red and blue fundamental sensations are apparently the same as those in normal trichromasy but the green sensation is of a different kind.\nThese abnormal trichromats seem to be quite common. They ave been described by Rayleigh, Donders and Koenig.1\nI have for several years tested my classes in the following way ; the origin of the test I have forgotten. A large red and a large green Maxwell disc are placed in the usual fashion on the axle of a motor ; a small black and a small white disc are then placed before the others. The room is darkened and a sodium light is produced by inserting salt (contained in a little platinum basket) in a Bunsen flame. Both sets of discs appear in grayish yellow. Their proportions are changed until they match. About 70% to 80% of my pupils agree on one match and the rest on a different one. This would seem to indicate a rather large number of abnormal trichromats. It is difficult to make any statement concerning how the world appears to these abnormal trichromats beyond saying that is certainly quite different-. Koenig and Dieterici\u2019s measurements suggest that the preponderance of green is shoved toward the red end of the spectrum. We might infer that for such persons our reds and oranges are more yellow, our yellows more green and our greens more blue to them. This might lead to some understanding of the peculiar colorings used by some artists.\nThe same principle of variation leads us to assume the existence of cases in which one of the fundamental sensations is entirely lacking. We thus would have \u201c red blindness, \u201d \u201c green blindness \u2019 \u2019 and \u2018 \u2018 blue blindness. \u2019 \u2019\nCases of acquired color blindness are presumably of this form. The excessive use of tobacco and alcohol quite frequently produces color blindness. Accidents, such as severe falls and contusions, may also produce it. Cerebral troubles, over-strain of eyes, and other diseases, sometimes result likewise.\nIn all such cases of acquired color defects we may readily assume the condition to arise by injury of the organ of one or more of the three fundamental colors ; it is thus a true \u201c color blindness \u201d for one of the colors red, green or blue.\n1 Rayleigh, Experiments on colour, Nature, 1881 XXV 67.\nDonders, Kleurvergettjkingen, Onderzoek. i. Labor, d. Utrecht. Hoogesch. 1883 (3) VIII 170.\nKoenig und Dieterici, Die Grundempfindungen u. ihre Intensit\u00e4tsverteilung im Spektrum, Zt. f. Psychol., 1893 IV 291.","page":14},{"file":"p0015.txt","language":"en","ocr_en":"A test of safe color vision.\n15\nMany persons have been found for whom it was possible to produce all colors by mixtures of two fundamental colors, a \u201cwarm\u201d color and a \u201c cold \u201d color. Such persons would be called \u201c dichromats. \u201d\nTwo distinct classes of dichromats are known ; they are said to be \u201cof the first class\u201d and \u201cof the second class.\u201d\nThe cold color of the dichromats is the same as the blue of the tricho-mats, the warm color is, in all probability, yellow, and not, as formerly supposed, either red or green.1\nThe two classes of dichromats differ only in the proportions of yellow found in any color of nature. The spectrum and all nature appear to them as systems of yellow, yellowish white, white, bluish white and blue ; particular objects in the two systems differ only in yellowness or blueness. It is inconsistent with the facts to speak of \u201cgreen blindness \u201d and \u201cred blindness \u201d; the only safe way is to use the terms \u201cdichromasy of the first class\u201d and \u201cdichromasy of the second class,\u201d as these will not imply a supposition that may prove incorrect.\nIt has been suggested that congenital dichromasy may be a phenomenon of atavism, or a return to the condition of color vision at a period in the ancestry of the animal kingdom when only two color sensations were present.\nStill another form of color-vision is found in monochromasy. All the visible objects are seen as shades of one color. What this color is, it has as yet been impossible to say. In cases of congenital monochromasy it is undoubtedly not red, green or blue.2\nWe can also expect cases of \u201cdouble color blindness\u201d to arise from the failure of two of the fundamental sensations. Thus we would have red, or green, or blue monochromasy. Such forms of monochromasy may occur in pathological cases. Other cases of acquired monochromasy seem to follow still different types.3\n1\tv. Hippel, Ein Fall von einseitiger congenitaler Roth- Gr\u00fcnblindheit bei normalem Farbensinn des anderen Auges, Archiv, f. Ophthalmologie, 1880 XXVI (2) 176 ; v. Hippel, Ueber einseitige Farbenblindheit, 1881 XXVII (3) 47.\nHolmgren, Flere Fall of ensidig F\u00e4rgblindheit, Upsala L\u00e4karef. F\u00f6rh., 1881 XVI 222. Also in Centralblatt f. d. med. Wiss., 1880, 898; Congr\u00e8s internat, p\u00e9riodique des sciences m\u00e9d., 8me Session, Copenhague, 1884; Ann. d\u2019Oculiste, 1884 XCII 132.\nKoenig und Dieterici, Die Grundempfindungen u. ihre Intensit\u00e4tsverteilung im Spectrum, Zt. f. Psychol., 1893 IV 345.\nHelmholtz, Physiologische Optik, 458, Hamburg und Leipzig, 1896.\n2\tKoenig und Dieterici, Die Grundempfindungen und ihre Intensit\u00e4tsverteilung im Spektrum, Zt. f. Psychol., 1893 IV 327.\n3\tKoenig, Ueber den Helligkeitstverth der Spektralfarben, Beitr\u00e4ge z. Psychol, u. s. w-> Helmholtz gewid., Hamburg, 1891.","page":15},{"file":"p0016.txt","language":"en","ocr_en":"16\tE. IV. Scripture,\nThe principles underlying these views of the nature of color defects can be more precisely stated in the following way.\nIf the amounts of red, green and blue be laid off on the rectangular axes, X, Y, Z, any color i will be given by\n* =f(x> y> \u00ab)\u25a0\nThe assumption that the function is of the form\ni= x +y + z,\nis recommended by its simplicity. Such a color equation means that any actual color seen can be represented as a compound consisting of certain quantities x, y, z of the three fundamental sensations X, Y, Z. It also implies that the composition is a simple addition of the three fundamentals\nFig. 6.\nwithout an influence of one on the other. Although this apparently does not hold with exactness for some phenomena of color, yet is valid within wide limits with close approximation.1 2\nSuch a color equation is represented in Fig. 6.\nIf r, g, b be taken as the strongest sensations of red, green and blue, obtainable in any person, the color-system for that person will be a pyramid whose base is rgb and whose apex is at the origin of coordinates (F'g- 7)-\nBy supposing that r\u2014g=b we have the right pyramid used by Lambert 2 to indicate the color system. This supposition is, however,\n1\tHelmholtz, Physiologische Optik, 376, 2 ed., Hamburg und Leipzig, 1896.\n2\tLambert, Farbenpyramide, Augsburg, 1772.","page":16},{"file":"p0017.txt","language":"en","ocr_en":"A test of safe color vision.\n17\nnot a necessary one. In fact, the general character of our whole constitution would lead us to believe that an equality of this sort is not the usual case.\nWe can justifiably apply to color certain principles that have been found valid for the whole organism. One such principle is that of variation. We can, at the start, expect that any property common to a\nr\nFig. 7.\ngroup of organisms will be found in various degrees in the various members of the group.\nApplying this principle to color, we may say that a given series of colors zj, zj, \u2014, in derived from the equations zj =\t+ y1 -f zv zj = x2\n+ y2 + zv \u2014 for one type of color vision might require slightly different equations for various individuals. Thus the same colors zj, zj, \u2022\u2022\u2022, zn might require the equations zj = xi +yt' + 2i> h = *i+y+ *,'> -, for a second kind of vision ; zj = xf + yf + zf, zj = xf + yf + zf, \u2014, for a third kind, etc. We might consider the type i = x + y -f z as the standard and express the varying individuals in terms of it by equations of the form i = ax + \u00dfy + yz where a, \u00df, y are coefficients changing for each individual.\nThe individual sets of values for a, \u00df, y may group themselves around various most frequent values and may represent types of color vision. We may say that a = \u00df = y = i is the expression for the normal type for which the equation is i = x + y + z. Any other group of individuals whose equations are similar enough to furnish a typical form may be classed as an abnormal type. All persons belonging to abnormal types might be called \u201c color defectives.\u201d\nThe fundamental principle of variation leads us to assume a type in which a is much less than \u00df and y. This gives an equation of the form 1 ~ a'x + \u00dfy + yz in which a' < /5 = y. The equations i = ax + \u00df\u2019y -f yz and z = ax -f \u00dfy + y'z would arise likewise for analogous types.","page":17},{"file":"p0018.txt","language":"en","ocr_en":"18\tE. W. Scripture,\nThese would be the equations of persons who have been called \u201ccolor weak. \u2019 \u2019\nWhen the variation is so great that a, \u00df or y become o, there arise cases of what is properly called \u2018 \u2018color blindness. \u2019 \u2019 Such persons might be characterized as \u201cred blind\u201d with the equation i =\u00dfyyz, \u201cgreen blind \u2019 \u2019 with the equation i = ax + yz, and \u2018 \u2018 blue blind \u2019 \u2019 with the equation i = ax + \u00dfy.\nOther types of variations of a, \u00df, y may occur but no data yet exist for stating the facts.\nIt is also quite possible that the three fundamental sensations may not be the same in all persons. In one class of persons already discovered the fundamental green sensation is different from that of the majority ; such \u201cabnormal trichromats\u201d would have equations of the form i = x + v + 2. The analogous types of abnormality like i = u + y -f z and i = x + y + w and also the subordinate types probably also exist but have not been discovered.\nThe two forms of dichromasy are characterized by equations of the forms i = u\\-\\- z and i = w2 + z. These also are to be considered only as typical forms from which the individuals vary just as in the cases of trichromasy.\nTypical monochromasy is indicated by i \u2014 p while the possible cases of double color blindness, or red, green or blue monochromasy, would be expressed by i '= x, i \u2014 y and i \u2014 z.\nThe preceding treatment is, as stated, based on the supposition of only three fundamental colors in normal trichromatic vision. If a fourth color is to be added, the treatment would be modified by the introduction of a fourth variable into the fundamental equation on p. 16, with the result\ni \u2014f (x> y> z> v)\nwhich on the usual assumption becomes\ni=x+y + z+v.\nIf this is the type of vision of the majority of eyes, the persons classed as normal trichromats (pp. 12, 16) are really tetrachromats and those classed as abnormal trichromats (p. 14) are really abnormal tetrachromats. The possibilities of variation in any or several of the fundamental sensations would lead us to expect to find among the forms of defective color vision four types of triple color blindness, i = x, i \u2014 y, i= z, i = v ; six types of double color blindness, i = ax = \u00dfy, i = ax + yz, i\u2014 ax + 5v, i = \u00dfy + yz, i = \u00dfy + Sv, i = yz + 8v ; four types of single color blindness, i = ax + \u00dfy + yv, i = ax + \u00dfy + Sv,","page":18},{"file":"p0019.txt","language":"en","ocr_en":"A test of safe color vision.\n*9\n/_ ax _(- yZ -(- Sv, i\u2014\u00dfy+yz + Sv, with numerous types of mono-chromasy, dichromasy and trichromasy in which several colors are combined in one fundamental sensation w (p. 15).\nOnly a few types of color vision are at present accurately known and a decision concerning the three or the four color theory cannot yet be definitely made.\nIn conclusion we may repeat that the forms of color vision are merely types of groups of individuals, that the members of a group vary from the type and that more extended examination of unusual cases would probably show most of the intermediate steps between the typical forms.\nIn the midst of such diversit\u00e9s in the types of color defect it would be hardly safe to base any test on the supposition, that the prevailing defect is of any one or two types. To suppose that all essentially important cases of defect belong to the two types of dichromasy known as the first and the second would be a neglect of somewhat numerous other types. Such a supposition is used as the basis for the Holmgren wool test ; it is evident that the various forms of \u2018 \u2018 color weakness \u2019 \u2019 and the like are not provided for. Furthermore, the Holmgren test is based on the additional supposition that the two forms of dichromasy are \u201c green blindness\u201d and \u201c red blindness \u201d\u25a0\u2014-a supposition that is unquestionably unjustifiable.\nUnder these circumstances the only safe method of procedure in selecting a test seems to lie in avoiding all suppositions while making the test conform as closely as possible to the conditions of actual practice.\nCharacteristics of the color sense tester.\n1.\tThe forms of color defect are so numerous and so various that a reliable test must be one that imitates the conditions found in the actual exercise of color vision. The color sense tester imitates these conditions closely.\n2.\tThis imitation of the practical conditions extends to the kind of object used, namely, colored lights under different conditions of brightness ; to the kind of decision required, namely, the character of the light ; to the kind of mental operation required, namely, a judgment after comparison.\n3.\tThe colored glasses are unchanged by use or time ; the test is a constant one and needs no readjustment or renewal.\n4- The performance of the test requires only a few minutes.\n3. The instrument can be used in a portable form. Employees can be tested on shipboard or on a train.\n6. The test is absolutely automatic. The decisions of the person tested","page":19},{"file":"p0020.txt","language":"en","ocr_en":"20\nE. W. Scripture.\nare recorded on the prepared blank. A comparison of the results with a list of the actual colors will render the decision immediately. No call is made upon the intelligence or color vision of the examiner ; it is only required that he shall record the answers honestly.","page":20}],"identifier":"lit28748","issued":"1900","language":"en","pages":"1-20","startpages":"1","title":"A test of safe color vision","type":"Journal Article","volume":"8"},"revision":0,"updated":"2022-01-31T15:19:33.861212+00:00"}