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{"created":"2022-01-31T14:29:40.197931+00:00","id":"lit28761","links":{},"metadata":{"alternative":"Studies from the Yale Psychological Laboratory","contributors":[{"name":"Seashore, C.E.","role":"author"}],"detailsRefDisplay":"Studies from the Yale Psychological Laboratory 1: 56-70","fulltext":[{"file":"p0056.txt","language":"en","ocr_en":"ON MONOCULAR ACCOMMODATION-TIME\nBT\nC. E. Seashoke.\nThough the limits of accommodation and related problems have received due attention from Helmholtz and others, the time of changing the focus of the eye has hitherto been scarce investigated. Yolkmann' seems to have been the first to experiment upon the subject. By applying Scheiner\u2019s experiment he found that he could change the accommodation of his practiced left eye 20 times from 11 in. to 6 in. and back in half a minute. Vierordt1 2 devoted a special treatise to the subject in 1857 and Aeby3 later examined the duration of the act of accommodation within the limits of 315mm. The latest and only important investigation on the subject that has come to the writer\u2019s notice is a series of experiments by Barrett.4 It will be referred to and compared with the present study from which it differs both as to method and results. The success of these experiments in Yale Psychological Laboratory is due to the efficient advice of Dr. E. W. Scripture, under whose supervision they have been conducted.\nThe problem I have undertaken is, to determine the time required to change the accommodation of the eye in either direction between two given points. As the object was the establishment, of fundamental laws and not the collection of statistical material, this research is limited to observations on the right eye of persons with a normal eyesight accommodating for points in the direct line of vision under the most favorable circumstances. The psychological method of differential reaction-time has been used because it is apparently impossible to determine the accommodation-time by any. direct physiological methods.\n1\tSehen, Wagner\u2019s Handw\u00f6rterbuch d. Physiol. 1850 III 1. Abth. 809.\n2\tVersuche \u00fcber die Zeitverh\u00e4ltnisse des Accommodationsvorganges im Auge, Arch. f. physiol. Heilkunde, n. F., 1857 117.\n* Die AccommodationsgeschwiHdigkeit d. menschlichen Auges, Zt. f. rat. Med., in. Reihe, 1861 XI 300.\n4 The velocity of accommodation, Joum. of Physiol. 1885 VI 46.","page":56},{"file":"p0057.txt","language":"en","ocr_en":"57\nMonocular accommodation-time.\nApparatus.\nThe variables are : (1) the distance of the nearer point, (2) the distance of the farther point, (3) the direction of accommodation, i. e. whether the focuB is to be changed from near to far or vice versa.\nThe solution of the problem required (1) an apparatus that holds the nearer point in view and suddenly exposes a point further off, (2) one that holds the further point in view and suddenly exposes the nearer point, (3) an arrangement to mark the instant the second point comes in view, (4) a reaction-key, (5) an apparatus for recording the time.\t^\nIn the first experiments I used a revolving disc having holes near the edge through which the further point could be seen. The nearer point was indicated hy objects on the disc at points alternating with the holes. The disc was arranged with weights, pulleys, springs and levers so that in its revolving it could be stopped to expose the nearer and the further point alternately. The person experimented upon was required to look through a tube extending from the eye nearly to the disc. One electric wire was connected with an isolated copper brush which made contact with the disc at the moment the second point could be seen. The brush was at all other points isolated from the metal plate by a cardboard covering. The other wire was connected with the disc and went through a closed-circuit reaction-key. Both wires were then run to the chronograph-room where they completed the circuit through an electromagnetic time-marker. Two markers were used on the drum. One registered the vibrations of the tuning-fork ; the other, running parallel to it, indicated the make and break of the current from the experiment room. To compare the two lines of the record perpendiculars were dropped from one line to the other at the points of make and break of the current.\nAfter the first and second sets of experiments I used another* apparatus which served the purpose better. With that I also used a simpler and more accurate method of recording. This latter apparatus consisted of a Laverne pneumatic camera-shutter to which electrical connections were added. There were two arrangements of the slide and the electric connections : (1) to drop the slide and expose the nearer point, (2) to raise the slide and expose further point. In the first arrangement one end of the electric wire was connected with the metallic body of the shutter. The other end was fastened to a binding-post which was connected (1) with a wire","page":57},{"file":"p0058.txt","language":"en","ocr_en":"58\nMonocular accommodation-time.\nspring which made contact with a projecting spring-arm on the slide at the moment the further point was cut off from view and the nearer point exposed, and (2) with a metal plate on which the projecting arm rested and made permanent contact when the slide came down. Both the contact-point and the metal plate were isolat\u00e8d from the metallic body of the shutter. In the second arrangement the slide was made to fly up and stop against a special catch. When the slide flew up its projecting arm struck the special contact spring at the moment the nearer point was removed from view and the further point was exposed. The special catch against which the slide finally rested at the top, and with which it made permanent contact was connected with the same binding post as the metal plate in the other arrangement. The current went through a closed-circuit reaction-key by means of which it could be interrupted. The current was made for an instant when the slide arm struck the special contact spring, permanently made by the slide arm resting on the metal plate or the special catch, and again interrupted by the reaction-key. The time required was that indicated between the first closing of the current and the breaking by the reaction-key. Heavy wires led from the shutter and the key to the chronograph-room where the circuit was completed.\nIn taking all except the first two sets of records I used the spark-coil method invented in this laboratory. For a full description of apparatus and method see the article by Bliss on p. 7-10. I did not, however, use the multiple-key described there but led the current directly to the research-room. A 100 v. d. tuning-fork was used but the drum was turned with such rapidity that the waves were sufficiently long to be easily estimated in tenths without error, thus giving me a direct record in thousandths of a second.\nThe nearer point was represented by a small capital o with a height of 0.7mir' and the further point by a large capital O with a height of 25mnl, except at the point represented as at infinite distance when a larger object had to be used. This object was a section in the crown of a distant chimney. The letter at the near point was on the slide. The other letter was on a card in a movable support.\nThe course of the investigation was somewhat in the following manner. First, the nearer point was kept constant at 20cm, and the further points made respectively 500m, lm, 2m, 4m, 8m, 12m, and infinite distance. A point over 100m away was considered the same as a point infinitely distant. Then the further point was kept constant","page":58},{"file":"p0059.txt","language":"en","ocr_en":"Monomlar accommodation-time.\n50\nat infinite distance and the nearer point was made successively, 20cm, 50cm, l\u00ae, and 2m. On these ten distances observations were made in accommodating the eye (1) from near to far and (2) from far to near. Both points lay in the line of direct vision. In this line was a tube extending from the front of the cornea in the eye of .the subject to within a short distance of the nearer object. The tubes were adjusted at a sufficient distance from the slide to allow light to fall upon the nearer object. There was a special tube for each near distance. The 20cm and 50cm tubes had a bore of 2cm. The lm and 2m tubes had a bore of 4om.\nPerson experimented on.\nThese results aim to be the records of a typical case. I selected a subject who could well represent the average and gave him the most favorable circumstances, i. e. a comfortable position, good light, medium temperature and avoidance of anything that would distract attention. The results thus have uniformity and comparative value because they are taken on the same person and, as nearly as possible, under similar circumstances. The subject was an exceptionally critical and reliable observer\u2014a fact of considerable importance where we have to trust to his judgment and faithfulness for the attainment of our results.\nThis series of observations was made on Mr. August Nelson, aged 29, a graduate student of philosophy. His eye is emmetropic with near-point 15\u00b0'\u201c and far-point oo ; volitional ability, as exercised in concentrating attention, excellent. Reacting over 4000 times to the same stimulus he acquired considerable practice. Practice may have shortened his reaction-time slightly in the later experiments, but the variation was not great as he had made nearly a thousand reactions before I took the records upon which this article is based. Of other subjects reacting to the same stimulus, some take a longer and others a shorter time than N. ; his records can be considered as representative of the average man.\nPrecautions and variations.\nReaction to a visual stimulus is a very complex act. It involves sensation, judgment, determination and other factors. In order to make the act as simple as possible precautions were taken to avoid intricacies and to facilitate perception. Thus, to avoid long and irregular time for discrimination and decision, the plain letter O was selected as the object for which to accommodate. The subject knew just what to expect and where to look for it.","page":59},{"file":"p0060.txt","language":"en","ocr_en":"Monocular accommodation-time.\nThe criticism was made during the investigation that it took time for the second object to \u201c clear up.\u201d It was \u201c blurred \u201d at first and \u201cgradually\u201d became clear. That is just the point here investigated, viz: the time required to change the focus of the eye so as to make a clear image. The subject was instructed to use his best judgment and react when the object became clear to him.\nMuch of the mean variation in time on any one distance we may ascribe to the fluctuation of attention. Its effect upon reaction-time is to be considered as established. In this case I think attention was the great factor in determining the fluctuations around the mean time of \u201c clearing up.\u201d\nAs a constant source of error I would mention the time that it took the slide to move a distance corresponding to the size of the letter at the nearer point. This time was less than 2\u00b0. Hence the uncertainty as to the time when one letter went out of view and the other was exposed cannot exceed \u00b1 lff.\nConsidering all the other objective sources of error, such as direction and strength of light, jarring of the apparatus and disturbances in the room, I would estimate that all the variations due to these do not exceed \u00b1 5\u00b0. The total limit of error was thus within \u00b1 6\u00b0. No uncorrected sources of error could be detected. In the earlier experiments where the unit of measurement was .01 sec. the latent time of the Deprez time-marker was quite negligible; in the later experiments with a unit of 1\u00b0, the latent time of the electric spark was far beyond negligibility, as was proved by experiments described in the article referred to above.\nMethod of experimenting.\nThe person experimented on was seated erect with the right eye before the tube. The left eye was closed but free to move. The reactions were made with the second finger of the right hand. The instructions were: \u201cLook sharply at the first O until the second O is exposed; when you see the second O clearly, react.\u201d\nThe time of the operation indicated on the drum included the time of changing the condition of the accommodation plus the time of reacting to a given stimulus. To get the simple reaction-time I proceeded as above except that the subject was required to focus for the second object only, or on the place where it was supposed to be, and, without any change of accommodation to react every time he saw the same object again. To get the accommodation-time, i. e. the time of changing the adjustment of the eye between two focal","page":60},{"file":"p0061.txt","language":"en","ocr_en":"Monocular accommodation-time.\n61\npoints, I subtracted the simple reaction-time. The records of the reactions were taken in sets of ten to twenty in each; hence, under similar circumstances. The first object was exposed about two seconds before the change and there was an interval of about ten seconds between each successive observation.\nI added all the records on each distance in a set and took the average. The tables give these final averages with the mean variation and number of experiments corresponding to each.\nResults.\nIn the following tables I use these abbreviations: N, nearer point;\nF, further point ; oo, practically infinite distance; F--> JV, from\nfar to near; F-----> F, from near to far; n, number of experiments\nof which the average is taken; A, accommodation-time ; R, reactiontime ; AR, accommodation-time plus reaction-time; MV, mean variation.\nTABLE I.\n(Curve I) N---> F. N= 20cm. Unit of measurement, .01 Bee.\nF\tAR\tMV\tn\tR\tMV\tn\tA\n50\"\u201d\t27.2\t7.4\t39\t26.5\t3.8\t18\t0.7\n1\u201c\t28.4\t3.1\t40\t26.5\t4.4\t16\t1.9\n2m\t34.8\t4.4\t37\t32.2\t3.7\t13\t2.6\n4\u201d\t36.1\t2.6\t31\t32.3\t4.0\t19\t3.8\ngm\t40.9\t7.6\t37\t35.5\t6.3\t20\t5.4\n12m\t41.4\t11.2\t40\t31.9\t5.7\t20\t9 5\n00\t40.9\t5.9\t40\t31.5\t4.5\t20\t9.4\nThe figures in tables I and II express hundredths of a second, the last figure being simply the decimal obtained in averaging a column. All the other records are in thousandths of a second. For the sake of comparison apd uniformity the first two curves are also marked","page":61},{"file":"p0062.txt","language":"en","ocr_en":"62\nMonocular accommodation-time.\nin thousandths of a second hut it must be remembered that they are based upon the figures in the first two tables.\na\nFig. 20. Curve I.\nThis table shows that when N is constant, the time of changing the accommodation of the eye from iV to F increases with the dis-\nTABLE H.\n(Curve II) N-----> F. F=cc. Unit of measurement,, .01 sec.\nN\tAB\tMV\tn\tR\tMV\tn\tA\n20cm\t40.9\t5.9\t40\t31.5\t4.5\t20\t9.4\n50cm\t40.0\t7.5\t40\t34.7\t5.6\t20\t5.3\n1\u201c\t32.5\t4.7\t35\t27.2\t3.5\t18\t5.3\n2m\t39.8\t7.8\t40\t35.5\t5.4\t20\t4.3\ntance of F up to 12m. Beyond 12m the time of monocular accommodation does not vary because the rays are practically parallel for all such distances. It will be observed that in proportion to the distance of F the greatest change in time is when F is near JV, and","page":62},{"file":"p0063.txt","language":"en","ocr_en":"Monocular accommodation-time.\n63\nthat the ratio diminishes to infinity as the distance between the two points is increased. a\nFig. 31. Curve II.\nWhen F is constant the time increases inversely with the distance of JV from the eye up to 2m or more. The greatest change in time\nTABLE HI.\n(Curve III) F--> N. Ar=20CI\". Unit of measurement, <r=.001 sec.\nF\tAR\tMV\tn\tR\tMV\tn\tA\n50cm\t169\t24\t40\t159\t30\t18\t10\nlm\t168\t22\t40\t165\t21\t19\t3\n2m\t178\t18\t40\t157\t12\t18\t21\n\t185\t33\t40\t163\t15\t17\t22\n8\u201c\t189\t27\t34\t166\t19\t12\t23\n12m\t313\t37\t37\t152\t19\t10\t61\n00\t250\t29\t34\t206\t19\t20\t44","page":63},{"file":"p0064.txt","language":"en","ocr_en":"64\nMonocular accommodation-time.\nis when JV is near the eye. The law of relative variation is the same as in table I, i. e. within certain limits the accommodationtime varies with the distance between iV and F, though this variation is not in proportion to the distance. a\nFig. 22. Curve III.\nThe same general law is brought out here as in table I; but in this case (F----> F) the time is shorter and the mean variation is\nTABLE IV.\n(Curve IV) F --> JV. F=ao. Unit of measurement, <r=.001 see.\nJV\tAR\tMV\tn\tR\tMV\tn\tA\n20\"\"\t250\t29\t86\t206\t19\t20\t44\n50cm\t267\t51\t33\t203\t16\t19\t64\nlm\t214\t19\t40\t178\t17\t20\t36\n2m\t205\t18\t40\t162\t15\t16\t43\nless than in the other (N---> F). From a comparison of AR and\nR in this table it becomes evident that the deviation in the case","page":64},{"file":"p0065.txt","language":"en","ocr_en":"Monocular accommodation-time.\n65\nof the last figure is wholly due to an exceptionally long reactiontime.\nFig. 23. Curve IV.\nThis is complementary to table III, and corroborates the same principles for the case where the nearer point is constant.\nTABLE V.\n(Curve V) AR taken F----> N and V-----> F alternately. V=20om. Unit of\nmeasurement, u=.001 see.\nF\ta F\t> N\tMV\tn\t6 N\t> F\tMV\tn\tb\u2014a\n1\u201c\t174\t18\t40\t183\t13\t28\t9\n2\u201d\t184\t37\t39\t220\t18\t36\t36\n\t211\t35\t38\t229\t22\t38\t18\n8\"\t269\t44\t38\t297\t71\t35\t28\n12m\t335\t65\t34\t398\t105\t29\t63\nCO\t243\t65\t40\t363\t102\t40\t120\n5","page":65},{"file":"p0066.txt","language":"en","ocr_en":"66\nMonocular accommodation-time.\nThe purpose of this set of experiments is to adduce further proof for the facts brought out in tables I and III, and to show how the\nFig. 24. Curve Y.\ntime is influenced by the direction of accommodation. This table is a comparison of Alt taken in series of 20 in each direction alter-\nTABLE VI.\n(Curve VI) AH taken F----> N and N-----> F alternately. F = oc. Unit of\nmeasurement, <r=.001 sec.\nN\ta F\u2014\u25a0> N\tMV\tn\t6 N\t> F\tMV\tn\tb\u2014a\n20cm\t243\t65\t40\t263\t102\t40\t20\n50cm\t193\t19\t30\t229\t26\t35\t36\nlm\t208\t28\t27\t222\t29\t30\t14\n2m\t187\t25\t32\t244\t48\t26\t57\nnately. It conforms to the principles laid down in tables I and III, and also shows that the difference between AH taken F-----------> N and","page":66},{"file":"p0067.txt","language":"en","ocr_en":"Monocular accommodation-time.\n67\nN------> F varies with the distance of F up to 12m when N is con-\nstant.\na\nFig. 25. Curve VI.\nWhen F is constant, the difference between the A1\u00cf taken F------> W and the AF taken iY-----------> F varies inversely with the\nFig. 26. Curve VII.\ndistance of N up to 2m or more. This is complementary to table Y, and confirms the same principles.","page":67},{"file":"p0068.txt","language":"en","ocr_en":"68\nMonocular accommodation-time.\nCurve V shows the difference in time depending on the direction of accommodation. This difference is further proved and illustrated by other data in curve VII, which is a comparison of the simple accommodation-time as given in tables and curves I and III. In the same manner curve VIII, complementary to curve VII, is a com-\n<7\n100\n90\n80\n70\n60\n50\n40\n80\n20\n10\n0.2\t0.5\t1\t2m\nFig. 21. Curve VIII.\nparison of curves II and IV, and proves with A the same principle as curve VI proves with AH.\nAside from the time itself and minor conclusions which may he drawn from these figures, three important principles have been established.\n(1)\tWithin certain limits the accommodation-time varies with the distance between the points for which the eye is to he accommodated.\n(2)\tIt takes longer to change the accommodation from near to far than from far to near, and this difference in time varies directly with the length of the accommodation-time.\n(3)\tFor equal distances in the same range the accommodation-time is greatest for points near the eye and decreases with the distance of the points from the eye.\nFrom the second fact arises the important question: what is it in the mechanism of the eye which will account for this difference in time depending on the direction of accommodation ? It may be due","page":68},{"file":"p0069.txt","language":"en","ocr_en":"Monocular accommodation-time.\n69\nto the difference in time required for relaxation and contraction of the muscles controlling the lens, or to the difference in range of movement and sureness of adjustment in changing the form of the lens to focus for points at different distances from the eye. For a satisfactory answer to that question we must, however, look to further investigation on the physiology of accommodation.\nComparison with previous results.\nBarrett\u2019s apparatus consisted of a skeleton compound microscope, supplied with electric connections by means of which the time was recorded on a drum. The experimenter carefully pointed out and obviated many errors of previous workers, yet his apparatus necessarily involved three sources of error which have been avoided by the apparatus in the Yale laboratory.\n(1)\tInstead of using lenses, as Barrett did, the eye was required to look directly upon the object to be accommodated for.\n(2)\tHis apparatus measured accurately to 0.1 sec. only, while the present apparatus measures with accuracy within \u00b10.006 sec. That his apparatus not only contained some great error but also gave very inaccurate records, can be seen from the frequent remarks, \u201c time too short too be measured.\u201d\n(3)\tThe greatest error is, perhaps, due to his method of deducing the simple accommodation-time. The present method of observing the reaction-time (without any movement of accommodation) to the same stimulus, for each distance and under exactly the same circumstances is the only trustworthy plan. Barrett arbitrarily subtracted 0.4 sec. in all cases.\nAdditional records on six other persons, which have not been introduced into the tables in order not to disturb their value for comparison, agree with Barrett\u2019s conclusion, that accommodation-time varies according to different circumstances, of which the principal are (1) age, (2) practice, (3) individual characteristics and (4) time of day.\nIn regard to fatigue, however, my results are contrary to the usual supposition. Experiments of some 300 accommodations in one continuous set do not support that theory. Fatigue soon sets in and may become very painful, but as long as the eye can accommodate clearly it causes a fluctuation in time which tends more to accelerate than to retard the velocity of accommodation.","page":69},{"file":"p0070.txt","language":"en","ocr_en":"70\nMonocular accommodation-time.\nThe most surprising deviation from previous results and theories is the conclusion drawn from my tables as to the relation of velocity in accommodation between near to far and far to near. Vierordt, Aeby and Barkett all agree that the accommodation-time is greater than the relaxation-time, i. e. that it takes longer to accommodate from far to near than from near to far. This statement is contradicted by every table and diagram given above.","page":70}],"identifier":"lit28761","issued":"1892-1893","language":"en","pages":"56-70","startpages":"56","title":"On Monocular Accommodation-Time","type":"Journal Article","volume":"1"},"revision":0,"updated":"2022-01-31T14:29:40.197936+00:00"}