-^w^ ^u ^ff 'M [|I»N THE EFFECT OP ASE ON HABIT FORllAT I OH IN Tffi ALBIHO RAT. DISSERTATION Submitted to the Board of University Studies of the Johns Hopkins University in con- formity with the requirements for the Degree of Doctor of Philosoj-hy by ;IEN B. HUBBERT. Baltinore, Maryland, June, 1915. no.^4.rork could not have been brought to a STiccesaful conclusion. Dr. Knight Dunlap , Associate Professor of Psychology at The Johns Eojkins University, offered much needed assist- ance in the handling of the data. Dr. Gardner C. Basset, of the Pittsburgh University, gave valuable suggestions regarding technique and method. Dr. Henry H. Donaldson, director of The Wistar Insti- tute, furnished practically all of the rats used for breed- ing puri OSes as well as a few of those employed in the ex- perinent, and was most helpful in suggestions throughout the experiment. Dr. Shinkiski Eatai prepared anatomical data for each rat used in the experirrent, which cannot be adequately handled in this discussion, and which will probably be taken up in a separate jublication to aj.pear later. 4 THi. EFJJ'KOT OJJ' AGh OA HABIT FUHKiATIOU liJ THt ALBINO HAT. INTRODUGTIOU. The ].roblem ooncerning the relation of the age of an animal to its learning Gaj.acity forma the basis for the in- vestigation herein discussed. Exi.eriments were begun in the Psychological Laboratory of The Johns Hopkins University dur- ing the winter of 1912, and continued until the spring of 1915. HISTORICAL. So far as the writer has been able to determine, prac- tically no experimental work has been undertaken on the rela- tion of age to learning ability, although the importance of the problen has been generally conceded. In the field of human psychology, I^unn carried out a series of "substitution tests" on children in the grades, on normal school pupils, and on two elderly persons, to determine the relative rapidity of gain in ability to make the required substitutions. Her records were taken in the terms cf time, and showed that althoiigh the children gained much more rapid- ly than the alults, their actual rate of speed at the begin- ning was lov.er, and they did not reacli the same levol of effi- 1. I.^unn - Curve of Learning, Archives of Psychol. IIo. 12, p. 37. 5 cieucy within the limits of the experiment. Only two elderly aubjecta were obtained, hence too much reliability cannot be attributed to the results from the last group, but apparently, v.hile their initial rtte is intermediate betv.'ecn that of the children and the norrr.al school pupils, they fail to reach the final rate attaiiied by either of them. IJunn gives neither the average nor the rate of gain for this last group, but the form- er was easily obtained, and appears in the table below. Adults - first test - 42 sec. last test - 14 sec. Children- " " -384 sec. " " - 3?^ sec. Old persons'' " - 72 sec. " " _ 3^. sec. Gain in first 5 tests : Adults 16 seconds Children 34 seconds Gain in second 5 tests: Adults 5 seconds Children 14 seconds It would appear from these results that, if the rate of im- provement is the question considered, children learn about twice as fast as adults. Turning to the field of animal behavior we find a somewhat larger amount of experimental work on the matter under discus- sion, although practically all of it occurs as a side issue to some other problem. Slonaker undertook a study of the normal activity of the white rat at iifferent ages, hoi ir.g to ''ascertain how the age of greatest activity comi ared with that at 1. Slonaker, J.R., The Normal Activity of the White Rat at Different Ages, Journ. Comp . Meur. & psych. 17, (07), 342-69. 6 which the rats were moat capable of education." Kia conclusions which relate particularly to the subject of this discussion are as follows: "1. White rats of difference ages show a marked difference in their activity. 2. The very young rat and the very old rat are each notice- ably inactive. 3. These experiments indicate that the age of greatest activ- ity ranges between 87 and 120 days. 7. From these preliminary experiments no correlation can be made between the age at which they are most active and the age at which they learn most rapidly." In a later paj er he places the age of greatest activity for the males at ten months, and for the females at twelve and five- 2 tenths months. The daily activity increases with the advance in age until a certain age is readied, after which there is a gradual reduction till death occurs^ "The female is much more 4 active than the male." In this paper^ as in the earlier one, no attempt is made to correlate amount of activity with capac- 1. Slonaker. J.H., The Ilormal Activity of the Albino Hat from Birth to Natural Death, «bG., Journ. An. Behav. II, ('12), 20-42. 2. Log. cit. , p. 30. 3. Loc. cit. , p. 26. 4. Loc. .cit., p. 42. itj'^ to learn. Yerkea-^ raised the question of the relation of age to habit formation in the dancing mouse. Ee worked first on the acqi:isition of the v;hite-black disorimination hubit, and later on the learning of simple labyrinth pathways. The indices of modif iabiliti as given by the number of training tests requir- ed to complete the habit for dancers of one and four months respectively, show that the males learned the -.vl.ite -black dis- crimination habit more quickly at one month (30 days) than at four months (120 days) while the reverse was true of the fe- males. The female was superior to the male, however, in the formation of the labyrinth habit. In later work he finds that male dancers ten months old learn the labyrinth more rapid- ly than those one to two months old, while there is practical- ly no difference in rapidity of learning of one to two month and ten month females. The old dancers are somewhat suj,erior to the young in their ability to learn the labyrinth paths. With regard to the sensory habit he says: "1. The dancer at one month of age acquires a particular white-blac]; visual discrimination habit more rapidly than do older in'\ividuals. Prom the first until the seventh month there 1. Yerkes, R.i:., The Dancing Mouse , The :acmillan Co., Ii07. Z, Loc. cit. p. 2 74. 5. Log. cit. i . 275. 4. Yerkes, R.I.:., L^odif icability of Behavior in its relation to the Age and Sex of the Dancin.- House, Journ. Comp. rieurol. and Psychol. 19, (150&) 257-2 71. 5. loc. cit. pp. 266-267. Is a a-teady and marked decrease in rapidity of habit formation; from the seventh to the tenth month the direction of the change is reversed. These statements hold for both sexes. 2^. Younp males acquire the habit more quickly than young fenalcG, but between the ages of four and ten months the females 1 acquire the halit the more quickly." 2 Eaecker, in work on the I'exican axolytl, found that the habit of distinguishing betvieen wood and meat when offered to the animals in forceps, was learned with far greater difficul- ty by the young (nine month) individuals than by the old ones, whose are is not given. 3 Watson in his Animal Education, discusses work both on habits involving simple motor ability and on those requiring skill in manipulation. He concludes that "a young rat will solve for the first time more quickly than a mature rat any probler. conditioned on mere random activity, but that a problem involving associative activity and manipulation is more easily solved by the older animals." Ee found that with the simple saw-dust box the average time of entrance for t].e old rats was 85.50 minutes, while that for the young ones was 6.87 minutes and says further, "there is a gradation in the number of use- 1. Log. cit. p. 269. 2. Eaecker, Arch. f.d. ges . Isych. , 2^, 1-7j5. 3. .Vatson, J. 3., Animal Iducation, University of Chicago Press, 1903. 9 less movements made by rats at different ages. At thirty -five dajj-s of age, when physical activity appears to have reached its highest stage, the percentage of useless movements is larg- est. As the rats grow older, this superabundant activity dis- aipears, and in its place comes direction of activity." To summarize the main points in this brief historical sur- vey, we may note-. First: - That there is disagreement as to the age of greatest activity, Slonaker putting it first between eighty- seven and one hundred twanty days, and later at ten months for the males and twelve and five-tenths months for the females, while Wataon believes it to be at about thirty-five days; Second: - That Yerkes finds the labyrinth habit more easily learned by the old dancers than by the young, v.hile if Watson's interpretation is correct the reverse should be true; Third: - Yerkes concludes that the fe[;:ale is superior to the male in learning the labyrinth. APPARATUS AiJD lilOCEDlTRL. Albino rats were chosen as subjects in this investigation for several reasons: Slonaker, rVatson and Yerkes v.-orked with rodents, and we deaired to compare our results with theirs. Nearly two hundred animals were required for actual experiment- al work and many more than that had to be kept on hand to pro- vide for replacing any who might become unfit for work, and to allow for the usual liJSses through death and sickness. It has 10 been fonnd that white rats are easier to breed, handle, and care for in large numbers than any other anall mammal. For reasona wliich will appear later, we adopted tlie circular maze as our problem since it is generally conceded that the rat is pre-eminent among animals in his ability to tl:read a labyrinth, while his satisfactoriness as a subject for experimental work is attested by the number of experimenters who have employed him in various capacities. The rats were bred in our own laboratory as needed, in- breeding being carefully avoided and all possible care being taken to maintain uniformity of breeding conditions. All of the rats were weaned at from eighteen to twenty-three days,* and the sexes were separated at tliirty-five to forty days and kej t seiarate thereafter. The livin,?- cages were protected fror. mice and gray rats by screened compartments cons tri;c ted of pine and 1/4 inch wire mesh. Every two weeks the cages were thoroughly cleaned, the shelves washed with a disinfect- ing solution, and the rats dipped in a one j er cent solution of "kreso" to prevent the rise and spread of vermin. The animals were carefully watched and treated immediately upon the appearance of jarasite^;, so that they were kept continual- ly in a healthy condition. The diet consisted of milk-soaked bread given every day, and a mixture of cracked corn and sun- flower seed every other day. They seemed to thrive on this somewhat restricted diet, so that no additions were made to it * :io bed effects were noticed from this early weaning and the rata were found to be extremely active as early as the 16th day. See Slonaker, op. cit. p. SCO. 11 althoTish both Basaet and Ulrich uaed carrots and fruit occasion' ally. The rats were handled freely from birth, and consequent- ly were ^rerfectly tame and evinced no fear of the e>4.ariraenter. Special care was taken to tame any rat seeming a little v.ild, before beginning v\ork: with him, since it was believed that fear and timidity might cause irregularities in behavior, a belief which was substantiated during the course of the exi:eriment. It was deriired in this work to obtain not only a record of time but also a distance record of the learning process, since it was felt that this might throw considerably more light on the factors involved in learning than had yet been obtained. The raarre problem seemed to offer greater possibilities in this line than either sensory problems requiring a long and tedious course of ^preliminary training or problems of maniiula- tion permitting of movements In two dimensions which would be praotioally impossible to trace. We therefore selected as our problem the learning of the circular maze. Heretofore, the only data possible on such a proble.-n have been in terms of time and errors, the time being the only re- liable record since it is practically imi^ossible to evaluate 1 ? and standardize errors. With regard to this Hiaa Kicks sa^ "The prevalent practice of omittinp- all total and partial re- 1. Watson, J.B., Iloddy and Sooty Terrac?, Carnegie Pub. :io. 103, p. 24 9, note 1. 2. Eicks, V.C., The Relative Values of Different Curves in learning. Jour. An. Behav. I, 138-156. 12 turns from the error record, and of making no attempt to eval- uate varying degrees of error gives a curvo which ia not only worthless hut false" fp. 156). She says further: "The total distance criterion presents so many difficulties as to render it imrracticahle for ordinary v.ork. One difficulty lies in the natter of taking records accurately. The rats, after a few trials, run so rapidly that it is extremely difficult for one person to observe and record at the same time. To do this, it is necessary to mark off the maze into small segments and commit to memory some scheme of representation so that records can be jotted down in a purely automatic manner. The work of transcribing this record into distance terms and computing the same is very laborious. Eliminating these practical difficul- ties, the distance criterion is in some ways an ideal one. (italics mine.) There can be no divergence of practice as to what shall be omitted or included and results obtained by dif- ferent experiments ui on the same maze will be strictly compar- able." (page 154) "The distance and error criteria are funda- mentally alike. The distance curve is the better representa- tive of the progressive approximation of the act towards auto- matic accuracy. It portrays all the details of this elimina- tive process and it approximates the ideal of uniformity and regularity of descent. However, it is impracticable from the standpoint of recording and manipulating the data." These practical difficulties in "recording and manipulat- ing the data" have been cvercome, at least where small animals are the subjects used in the maze. The total distance can be 18 Plats I - The Maze. 14 obtained aocurately by means of the camera lucida attachment de- signed by rrof. 'w'atson (see plate I) for use with hia circular mas^e. This maze has a wooden base 150 om. in diameter and six aluminum runways 15.5 cm. high and 10 cm. v.ide. The entrances to the alleys are 10 cm. wide, and are at alternate ends of a quadrant arc. The radial stops in alleys 1 to £ are also i^lac- ed at alternate ends of a quadrant arc, the stoi. in each alley being directly opposite its entrance. Thus it is possible for a rat to run only l/S the circumference of a runway in either direction before being forced to turn. This is not true of ailey 6, where no stop is employed. The central circle, or food compartment is 20 cm. in diameter. A 3/4 inch mesh, wire top prevents the animals from escaping v.ithout interfering with observations of their movements. The camera lucida attachment consists primarily of tvvo mirrors and an achromatic lens. The arrangement is as follows: A large plate glass mirror is fas- tened by sui porting framework at an angle of. 45° v\ith its cen- ter directly above and 1.8 meters from the center of the maze. A somewhat smaller mirror is placed facing the first and making an angle of 90° with it at such a distance away that t.:e light reflected downward fal"'s outside the maze area. In the path of this reflected light is placed a single achromat, 6 om. in diameter and of 50 cm. focus^ in a mounting provided with rack and pinion adjustment which is fitted into the ceiiter of a wooden disc 30 cm. in diameter. Below this at the focus of the lens is jlaced a second wooden disc of the same diameter as the first, which serves as a holder for the paper Ui.on which 15 the ima(je of the maze is reflected. Both of these dlaca are attached to iron collars which slide independently up and down the rod CR.thus making it possible to vary the size of the image. A snail curtain of dull black velvet attached to the upper disc serves to exclude all extrarieous light from the re- cording table and as a further aid in sensitizing the eye, a large curtain of dark material encircles the space occupied by lens and recording apparatus as well as the experimenter's chair. This ciirtain also serves the purpose of completely hid- ing the experimenter from the animals while they are running in the naze. Illumination is obtained by means of six 40 watt tungsten lamps placed symrietrically around the maze and one 150 watt tungsten in the center. These lights are mounted on brass rods and fitted with aluminum shades blackened on the upper surface. The central shade is circular, those for the peripheral lights are half shades. The floor of the maze is covered v.ith white linoleum, which can be thoroughly scrubbed whenever necessary. The en- trance to the starting box is supplied vvith a hinged door which can be securely fastened after the animal has been placed in- side. The exit is provided with a sliding door which is rais- ed by means of a cord, and closes oi its own weight when the tension on the cord is released, thus making it impossible for a rat to return into the starting box after it has once enter- ed t}.e maze. 3y means of the two mirrors (V and i:'), and the lens (L), 16 'ig, 1 - Tracing of the actual path followed by a rat at one stage of the learning process. Pig. 2 - Ohartoneber, 17 an exact image ( I r ) of the maze is thrown on the recording table where the exj-erimenter can follow every movcme^nt of the animal during any j asaage through the maze. Actual records of these trij 3 are made by tracing on the record sheet v;ith a soft pencil the successive movements of the rat. (See Fig. 1) Theoe (5'i$.2) tracings, measured with a chartometer shown by calibration to be accurate to within one j er cent, form the basis for the dis- tance record. Since the maze is 6.4 tines as large as the image, the distance record obtained in centimeters by the char- tometer, must be multiplied by 6.4 to obtain the actual dis- tance traversed in the maze. For example, if the distance indicated by the chartometer is 121 centimeters we obtain the actual distance run thus, 121 cm. x 6.4 = 7744 cm. The values given in the tables represent the actual distance covered by the rats. Both chart and maze distances were tabulated, and the multiplications made to obtain the latter were checked on the adding machine, In addition to tne distance record, such charted pathways also furnish accurate account of the excess effort expended, enabling a comparison as to the frequency and extent of the several possible errors as well as a record of the exact steps in their elimination. It can be determined whether a certain error is lessened at each trial and finally dlsaipears, or whether it is dropped out all at once. In short, we have an accurate method of tracing the several fac- tors in-'olved in the learning of the maze i robleni, and a basis for the analysis of the learning process which has heretofore been lacking. The exact method employed in this research concerning the 18 relation of age to the learning ability was as follows: One week preceeding the day on which the animal was to begin work, food waa removed from the living cage and the rat was fed each day in the center of the maze v.'hich waa temporari- ly jartitioned off from the remainder, making it imj osaible for him to roam at will through the maze. The first day, he was allowed to eat for forty-five minutes; the second day, for thirty minutes; the third day, for twenty minutes. The feed- ing tine was then diminished five minutes on each succeeding day, 30 that the day before beginning the problem, the rat had been fed for five minutes in the food box of the maze. Tv;o things were accomplished by this procedure - lat: The rat was rendered quite hungry, a necessary stej , since food was the stiniilus used, but the shock which would have resulted from en- tire absence of food v/as avoided. 2nd: It becane accustomed to some extent to exi^erimeatal conditions. On the day when the problem was actually begun, the tem- porary partition was removed from the maze, a dish of milk- soaked bread placed at the center and the rat placed in the starting box (3. B. Plate 1]. The instant it emerged into the maze proper, the door (indicated but not shown in the illustra- tion} , was closed behind it making return into the starting box impossible, the stop watch was started and the tracing be- gun. TTwelve or fourte'3n minutes might be required to reach the 1. Grain was given in the cage each day at tlie orA of the feed, ing period. 19 food, and aa many as sixteen sheets of paper have been neces- sary to trace the pathway during a single trial. At the moment of entrance into the food box (F.B.), the watoh was stopped, the time noted, and the animal at once removed. This constitut- ed one trip or one trial. The rat was imn.ediately introduced for a second trial, in whieli the same procedure was followed excejt that on reaching the food it was allowed to eat for five minutes before being removed. Tlie feeding j.eriod was care- fully timed with the purpose of keeping the hunger stimulus as uniform as possible. A short ration of grain was throv.n into the living cage, and no more food was allowed luitil the next day's work. Basset had given grain only twice a week, and noted in consequence a disturbance in behavior on the day fol- lowing that on which grain was given. Ulrich^ fed his animals in the cage after work, which may account for their slowness in learning the maze as compared with the rate used in this problem. Two trials were given each day until the problen was learned, i.e., until in six trips made on three consecutive days no error was made from start to finish. In boti. Basset's and Ulrich's work, a time norm was set, and although no useless 1. Bassett, G. C, Eabit Formation, Scc, Behavior Ponograph 2, (1914), Ho. 4. 2. Ulrich, V/ork unpublished. 30 movements were made, unless the act was performed within the limits of the time set, it was not considered perfect. For the purposes of this experiment si:ty -five, two hundred, three hundred and five hundred days old res} ectively, since it was thought that these ages represented fairly well the successive stages in the growth and development of the animal; twenty-five days for youth, aixty-five days for sexual maturity, two hundred days for ma- turity, three hundred days for age, and five hundred days for old age. The attempt was made to have thirty rats in each groui , hilt sickness and unavoidable accidents among the animals have brought the number 3omev;hat lower. it has been found ex- tremely difficult to obtain rats for the last group (500 days). Although Slonaker finds the average length of life of the v.hite rat to be thirty -four months, and Donaldson gives it as three years, from tl^rea hundred to four hundred days is the ma>:imum longevity for most of the rats used in this laboratory, and up to this tire only ten have lived to work at the five hundred day age, one of these dying ap.iarently of old age before the problem was learned. The groups used, v.ith the number of rats in each group 1. op. cit. Jourl. An. Behav. jp. 37-38, tables. 2. Dr. r/atson has informed the writer that his exj crience was quite similar, very few of his rats living to be more than 500 to 600 daya old. were as follov.s; - Age at which work began number of rats in the grou>v 25 days 8 7 65 " 27 200 " 28 300 " 28 500 " 10 Throughout the exi.eriment two conditions have been rigid- ly conii lied vath. 1st: Every animal was started on the problem ui on the exact day at which the proper age was reached. This procedure was follov.ed even when it necessitated starting eighteen rats on the same day, in order that exj erinental con- ditions night be kej: t strictly comparable. 2ad: Kvery animal was run twice every day fron its first trial until tiie last, even though at one stage of the work this required having as many as fifty -eight rats under observation at one time. Such strict continuity of trials precluded the introdiiction of any factors aside from those involved in the learning process proper. Removal from experimental conditions for even one day would not only cause a change in the physiolog- ical tonus of the organism, but would also bring in the matter of retention. 3o far as was possible the rats were run at the same hour each day, but where large numbers were being used it was impossible to adrere strictly to this rule, although rats accustomed to run at night did not do so well if used in the morning and vice versa; which was probably attributable to the acquiring of a certain food rythm that might not be broken with impunity. Thus it was found that while a difference of an hour 23 in the working time, and henoe the feeding time caused no notice- able change in the behavior of the rata, marked disturbance re- sulted from a delay of four or five hours. In general, the behavior of individuals of each group on first entering the maze was the same. The rats showed great hesitancy in leaving the starting box^ returned to it frequently after finally entering the maze proper, and endeavored to push up the sliding door; they were also to leave a familiar alley for one unexplored, became excited when a stop was encountered, trying repeatedly to push it aside or to gnaw through the mesh top, and made frequent efforts to escape from the maze. Departure from this type of behavior was noticed among the very old rats aad the very young ones. Many of the former evidenced no excitement whatever, often slee^-ing for several minutes between periods of activity, while the latter were far more ac- tive than the rats of any other group, and showed no hesitancy in entering unfamiliar portions of the maze. The time usually decreased very rapidly, the distance less so, during the first three or four trials. For example, on its first trial, rat 34 of the 300 day group required eleven minutes and forty seconds to reach the food and the distance covered was forty -nine and six-tenths meters. On its second trial, seven minutes six seconds were required, and the distance run vias thirty and nine-tenths meters; at the fourth trial success was attained after 1 minute nineteen seconds; the pathway traversed measuring ten and two-tenths meters, while for the sixth trial the time record was only forty-nine seconds, the distance eight and six- tenths meters. By the tenth or fifteenth trial the decrease in 24 both tine and distance become much more gradual, and continued 30 until the problem was learned. Tlie rat roferrei to above re- quired on the fifteenth trial twenty -four seconds, and ran seven and two-tenths meters, on the thirtieth trial the trip occupied fourteen seconds and covered five and six-tenths meters. This ] articular animal completed the problem at the sixty-sixth trial when the time record was seventy and two-tenths seconds and the distance record four and five-tenths meters, which, it will be remembered, constitutes a perfect run. The data set forth above may be conveniently tabulated thus Distance run in maze be- Trial Time required to reach fore reaching food. (The food true pathv»ay 4.5 M. ) 49.6 meters 30.9 10.2 8.6 7.2 5.6 4.5 This rapid decrease in time and distance at the beginning of the problem was characteristic ai all groups, and is clear- ly shown in the initial drop in all the curves. The Twenty-five Day Rats. Work on this group began at twenty-five days when the rats were so small that they could crawl through the mesh toi- of the maze, and could touch the sides of the alleys only by running from side to side, while other rats could remain in the center of the path and touch both walls of the runways with 1st 11 min. 40 sec 2nd 7 " 6 " 4 th 1 " 19 " 6 th 15th 30 th 49 " 24 " 14 " 66th 7.2" 25 their vibrisaae. Theae rats were weaned at eighteen days, and were fed in the maze for five daya preceding the experinent, the forty-five and thirty minute feeding perioda being omitted. For the first day or tvvo after starting the problem, they were allowed to eat for six or seven minutes instead of live miuutes at the end of each day's work, since it developed that a short- er ration had a weakening effect on animals so young. The lit- tle rats %ere exceedingly active, and on entering the maze ran so rapidly that it was very difficult, but never impossible, to trace their movements. For the most part they showed great eagerness to escape from the starting box, some even acquiring the habit of lifting the door partway with the nose, and as a rule they had no hesitancy in entering unexplored portions of the naze, in this resject differing from most of the rats in this experiment. The error of circling the food box occurred more often with rats of this group than Aith those of any other, the explanation being, perhaps, that in their over- eagerneas to reach the food they acquired such momeatum than they ran past the entrance to the food box. Twenty-seven rats were experimented with at this age, eleven males and sixteen females, eight straias being repreaent- ed,as fellows: Wl! ,/^j^ Y f C F )z/,^u G Jy/^'/f AL ^'4/4 XL ^J's/n Y L fo/,^ Z 7; '//m T.Y i'M Al 1 Males C 2111 51 2 11 Females 2 1113 55 0 16 Total 2 3 2 2 4 8 4 2 2 7 26 The first letter indicates the father, the second letter the mother, of the litter. Indlviiual rats were distingruishable fron each other by a convenient syatam of ear marks, and on every cage was a tag showing the e>:j erimental number, parentage, late of birth, dex and ear mark for each rat contained therein. Thus, W M 1/9/14 H-± 4, would be deciphered, rat number four, female, right ear straight, born January ninth, 1114, mother !', father W. Tlie number of trials required by animals of this group in learning the problem varied from fourteen to fifty-one, the absolute time from four and nine-tenths seconds to nine and one- tenth seconds, the total time from siity-four minutes to six hundred forty -nine minutes; and the total distance from one hundred thirty-nine meters to four hundred eighteen meters. The "absolute time" is the average time for the last six trials, represents the limit of efficiency in speed for a given group, and varies among individual rats ivithin the group as well as for the groups themselves. Thus, the record time for the twenty-five day group was made by a rat which could ruji fron entrance to food box in four seconds, but no other rat at- tained this speed, and one in particular could not make the run in less than eight seconds. The last six trials were all with- out err^ r and would seerr. to afford a fair basis for judging the average final efficiency, which for thi.. group was five and aeven-tenths seconds. The ab^^olute distance is the same for each group, since the last six trials are errorless, and the true pathway measure.: approximately four and five-tenths meters. The enormous number of figures involved, makes the showing of individual records inexpedient. An exact copy of the daily record for rat number fifteen of the twenty-five day groujc , from the first to the last trial appears aa Table I. The averages a>id totals for each rat which appear in Table II are obtained by adding and averaging the daily records for each rat. Trial, time and distance variation for each animal are also given. The total time, total distance, total number of trials and the absolute time of the twenty-seven rats v.ere added and averarred to give the average total time, the average total dis- tance, the average number of trials, and the average absolute time for the grouji . The ST eed is the average nuijiber of centimeters traveled per second throughout the learning procesp, and is obtained by dividing the total time into the total distance. For the twenty-five day group these averages were: Trials Time Distance Speed Absolute Total 30 5.7 sec. 224 min. 271.6 meters 20.1 The curves shown in Fig. 3 are based on the I'igures in columns 2, 4 and 6 of Table II. Only one rat finished in less than fifteen trials, and this is indicated on the first point 01 the curve. Three rats finislied at between fifteen and twen- ty trials, one at seventeen and two at eighteen trials each, the average being seventeen as indicated on the curve. Between TABLE I. Rxin In day time Eat 15 - 26 days Distance X L 3/l5/l4 B_ male Day Trial Time Seconds Chart Uaze 1248.0 Ellm. 4-5-6 896.0 " 3-4-6-wronc turn-1 C78.4 Elim. 1-3-4-5 448.0 Perfect 25.8 158 1011.2 Elim. l-2-4-5-6-Lo8t in 3 768.0 " 2-4-5-6-w.t.l-3 460.8 " 2-3-4-5-6-w.t.l 678.4 •• " " " 10.4 70 448.0 Perfect 25.8 120 768.0 Elim. 2-4-5-6-w.t.l-3 6 70 448.0 Perfect 19 132 844.8 Elim. 3-4-5-6-w.t.l-2 5.6 70 448.0 Perfect 6.2 70 44.8 " 11.8 99 633.6 Elim. 2-3-4-5-6-ret.-l 32.4 129 825.6 •♦ 2-3-4-5-C-ret. , w.t.l 4/9/4 1 2 1,7.8 67.8 37.2 195 140 2 4/10 3 4 15 10 106 70 3 4/11 5 6 25.8 17.4 158 120 4 4/12 7 8 11.8 18.6 72 106 5 4/3 10 6 4/l4 11 12 7 4/15 13 14 8 4/16 15 16 TABLE I (Continued) Run in day time Eat 15 - 26 days Trial Time Distance Seconds Chart Maze X L 3/15/14 B_ male 9 4/17 17 18 10 4/I8 19 20 11 4/19 21 22 12 4/20 23 24 13 4/21 25 26 14 4/22 27 28 4/23 29 30 16 4/24 31 32 17 4/25 33 34 7.8 5.4 70 446.0 Perfect 7.4 83 531.6 Elim. 2-L^-4-6-6-w.t.l 5.4 70 448.0 Perfect 5.2 70 448.0 n 6.4 70 448.0 Perfect 6 72 460.8 Elim. 2-3-4-5-6-too far 5.2 70 448.0 Perfect 9 101 464.4 Elim. 2-3-4-5-6-w.t.-l 5 70 448.0 Perfect 5.6 70 448.0 •• 7.6 72 460.8 Elim. l-2-3-4-6-w.t.-5 5.4 70 448.0 Perfect 5 70 448.0 '• 5.2 70 448.0 r« 4.8 70 448.0 Finished 4/25/14 4.4 70 448.0 34 Trials 4.6 70 448.0 " 5.6 70 448.0 n 80 twenty and twenty-five trials three rata finished, at twenty- three, twenty-four and twenty-four trials resj.eotively; the average is twenty-three, and the third point on the curve in- dicates that three rats finished at twenty-three trials. The same procedure is followed in drawing the time and distance curves except that they are necessarily more condensed. Three rats required approximately four hundred seconds each in which to learn the problem, (numbers 11, 15 and 24], and the first point on the time curve indicates this fact. The fourth point shows that six rats consumed from fifteen thousand to twenty thousand seconds (average for the six seventeen thousand sec- onds), in their total number of trials. The fifth point in the distance curve is interpreted to mean that six rats cover- ed between three hundred thousand and three hundred fifty thous- and centimeters, (average for the six, one hundred seventy thousand), in learning the maze. It might be well to notice at this point that all of the curves appearing in this paper are constructed on this same plan. The trial curve, (Pig. 3-A) for this group reaches the apex at about thirty, which is the average number of trials for this age . Two maxima appear in the time curve, (Pig. 3-B) at eight hundred seconds, and at seventeen hundred seconds re- spectively. A point intermediate between the two v.ould give the tine average for the group, approximately thirteen hundred seconds. The apex of the distance curve, (Pig. 3-C ) , is at three hundred thousand centimeters, which is not far from the grouj, TASUC 11-25 DAY RATS. 81 11 males - 16 fema les Hat Trials Trial Tirae(3eos) Time Var. Distance Dist.Var. Abso- Dev. (cm) lute T. "d^" 4 18 12 2541.4 -1196.3 18035.2 9127.1 5.7 6 45 -15 1903.4 - 558. 3 38666.8 -11504.5 5.1 8 32 2 959.8 385.3 36732.4 -9570.1 5.3 10 20 -2 699.6 645.5 23770.4 3091.9 5.0 15 34 -4 423.2 921.9 19424.0 7738.3 4.9 16 27 3 1592.2 -247.1 30016.4 -2044.9 5.5 19 4c -10 721.2 623.9 29207.2 11030.7 5.5 24 24 6 388.4 956.7 16131.6 -2854.1 6.1 27 51 -21 1588.0 -242.9 41816.0 -14553.7 5.6 26 30 0 1603.2 -258.1 28454.4 -1292.1 9.1 37 30 0 1632.8 -287.7 23070.4 4091.9 5.5 ? 1 23 7 2623.2 -1278.1 37819.2 -10656.9 7.2 2 26 4 562.2 782.9 21913.6 5248.7 5.5 " 5 14 16 3897.2 -25 r 2.1 30348.8 - 3186.5 5.2 9 38 -8 723.6 621.5 27129.6 32.7 5.4 11 18 12 401.4 943.7 13900.8 13261.5 5.7 12 32 -2 2381.0 -1035.9 32648.8 - 5486.5 6.1 13 46 -16 999.4 345.7 30407.0 - 3244.7 4.9 14 24 6 519.6 825.5 18553.6 8608.7 5.6 17 26 4 612.8 732.3 18771.4 8390.9 5.6 20 34 -4 945.6 399.5 25779.2 1383.1 5.3 21 36 -6 900.6 444.5 26208.0 954.3 5.1 22 32 -2 536.2 808.9 23979.2 3183.1 5.4 25 36 -6 597.6 747.5 30882.8 - 3720.5 5.2 28 28 2 2643.2 -1298.1 36672.0 - 9509.7 5.2 31 44 14 1838.2 - 493.1 30332.2 - 3169.9 5.2 41 17 13 2082.8 - 737.7 23212.8 3949.5 7.6 Totals 822 19 7 36317.8 20370.7 733383.8 161686.5 153.5 Av»r- 30 7 1345.1 754.4 27162.3 5988.3 5.7 Eg«S Average for e/;3 BH '^y^ff/^ BH ^H'^ V.B'^^ZL ^/o/^Total 1 1 3 1 2322 15 0 2 2 2 4201 13 Total 1 3 5 3 6523 28 Trials varied in number from fourteen to one hundred twelve, absolute time varied from five and tv.o tenths seconds to twenty - four and one tenth seconds, total time from eighty-two to nine- hundred forty -nine minutea, and total distance from one-hundred twenty-five and five tenths meters to nine-hundred and twelve neters. As for previous groups trials bear little relation to time or distance, but the proportion between total time and to- tal distance is fairly constant. f3ee Table IV) The lowest trial record was fourteen, and the time and distance records for the rat making this record were also low. The lowest time record, as 'Aell as the lowest distance record was made by a rat finishing in twenty trials. The rat requiring the largest xium- ber of trials (112) had a time record but little higher than one which required only thirty-four trials, vrhile its distance record was next to the highest. The highest time record was that of a rat which finished in one hundred aeven trials, with the next to the highest distance record, the higliest distance TABLE lY - 2U0 DAY RATS. 16 Males - 13 females 40 Eat Trials Trial Dev. Time (SecsJ Time Var. Distance (om) Dist. Var. Absolute T 2 18 24 b 28 14 8 44 - 2 9 26 16 10 20 22 11 20 22 23 30 12 24 30 12 29 lOi -62 30 107 -65 31 64 -22 33 32 10 34 22 20 36 32 10 38 14 28 810.2 1548.2 1767.0 646.3 496.4 1548.6 1191.0 1564.8 2636.1 4735.6 1877.2 1343.8 1084.6 777.8 732.8 1298.9 560.9 342.1 1462.8 1612.7 560.5 918.1 544.3 - 527.0 -2626.5 231.9 765.3 1024.5 1331.3 1376.3 15010.4 30275.2 16672.0 12559.2 18387.2 22828.8 28355.2 64632.2 91293.8 47627.2 25446.4 18240.3 18675.2 12569.6 18900.7 11978.7 3635.9 17239.1 21351.9 15523.9 11082.3 5555.9 -30721.1 -57382.7 -13716.1 8464.7 15670.8 15235.9 21341.5 8.7 8.6 10.7 5.7 6.8 7.4 7.0 7.6 17.3 24.1 6.5 8.5 10.5 8.1 7.9 3 26 16 4 112 -70 6 18 24 7 54 -12 15 32 10 17 56 -14 18 79 -37 19 49 - 7 20 27 15 21 32 10 25 35 7 27 22 20 35 37 5 Totals 1170 588 AVfarages 41.7 21. 1280.4 3014.0 1825.2 3851.1 2409.0 2995.8 3663.4 2031.4 5694.8 2440.0 2990.6 963.4 3135.8 36294.9 2109.1 828.7 19744.0 14167.1 9.4 - 904.9 69781.6 -35870.5 7.4 283.9 13475.2 20435.9 8.0 -1742.0 51143.4 17232.3 7.2 - 299.9 31522.8 2388.3 5.2 - 886.7 46335.8 12424.7 6.5 -1554.3 59373.2 25462.1 6.6 77.7 44944.4 11033.3 5.4 -3585.7 32960.0 951.1 8.7 - 330.9 35686.0 1774.9 6.1 - 881.5 35697.6 1986.5 7.8 1145.7 19043.6 14867.5 7,8 -1026.7 45104.8 11193.7 7.3 28731.7 949517.5 437589.1 238.8 1026.1 33911.1 15628.1 8.5 1012.2 29633.6 17186.7 9.7 1042.2 38847.1 13060.5 7.2 At. foro" 39.4 23 1517.3 " " ? 44.5 19 2791.9 41 TWO HUNDRED DAY BATS Pig. o en 5 ^ M 4 S3 M 2 UNIT = 1 10 20 30 40 oO 60 70 30 dO 100 110 120 HUMBBR OP TRIALS UNIT =» 10 11575 200 SOO 400 500 — 600 700 TOTAL TIME (SECONDS) 800 900 IQOO 1100 1^0 35 0 i 4 UNIT = 100 100 200 300 400 500 600 700 TOTAL DISTANCE (CENTIUSTSRS) 300 930 1000 1100 1200 42 record by one finishing in twenty-sevon trials, whose time was consiierably above the average. The averages for this group are-. Time Trials Absolute Total Distance J] eed 42 8.6 sees. 351 min. 35&.1 m. 16 cm. per sec. The apex of the trial curve, (/ig. 5-A,)lies at thirty-three, while the average for the group is forty -one, but the explana- tion of the apparent discrepancy is to be found in the records of the six rats who required from fifty-six to one hundred twelve trials to learn the problem, thus running the group average up. No well defined apex can be found in the time curve (Pig. 5-S) the group average, twenty -one hundred seconds showing rather as a depression, nor could it be divined by a glance at the dis- tance curve that the average lay in the neighborhood of thirty- three thousand cm. The average mean variations are: Trials 42 ± 21 bZ'fo variation Time 852 min. ± 171 min 48/^ Distance 339.1 m. ± 156.2 n 46';^ " The distance variation is again the least. If the averages for the males and females be compared, it appears that the former are somewhat superior to the latter ex- cept in absolute time. The averages are: Time Trials Absolute Total Distance Males 39 9.7 sec. 219 min. 296.3 m. Females 45 7.2 " 465 " 388.4 " In the matter of mean variation, the males have the lower time variation, but the female distance variatioa is lower. The figures are: Time Variation Distance Variation I'ales 169 sec. 171.8 m. Females 173 " 130.6" Three Hundred Day Rats. This group consisted of twenty-eight rats from ten fami- lies, thirteen males and fifteen females, who began the jroblem when three hundred days old. AD- wl/„ BD^= r/,a WF ^/"/2 BY'H'zi ,'fVV'2 BFy^/, CF^/ 4|,BE^/ */.CF^/^Total 0 1 1 4 0 1 1 1 0 4 2 1 2 2 1 2 1 2 13 0 15 Total 1 5 1 2 2 6 3 3 3 2 28 They were fed in the maze for ten days before the beginning of 44 the problenn, preliminary feeding being thua exteniecL bectuse it was found that rats so old contracted digestive troubles unless the decrease in food supply was mala more gradual thhn for the younger animals. They were allowed t- eat for from six to eight minutes instead of five, at the close of each day's work, since they ate much slower than the younger rats, and could not obtain sufficient nourishment in the shorter time. These rats differ- ed markedly in behavior from those in any of the preceding groups in that they were lethargic, inactive, and often went to sleep in the naze instead of working at their problem. A few of the animals of this group were from The 'Vis tar Institute, and were somewhat timid and difficult to handle, but even among animals bred in this laboratory the same disinclination to v/ork was noted although with our own rats it id not last so long. V/hen the rats finally begun to work, they went about it differently from those of other groups. They were very deliberate, follov.ed the culs de sac out to the bitter ead whereas the other rats often turned back toward the true path before reaching the alley stop, furthermore, they did not hesitate to enter the unexplored run- ways as dii most of the other rats, in this last respect resemb- ling the twenty-five day rats. The trials varied from fourteen to eighty-four, absolute time from five and eight tenths seconds to thirty-five and two tenths seconds, total time from one hundred nine minutes to two thousand two hundred seventy-foir minutes, and total distance from one hundred seventeen and three tenths meters to six hun- dred nine and six tenths meters. 45 No conneotion between number of trials and time or dis- tance was found, and the ratio of total time to total distance did not a^j^ear to be constant. (Table V). Thu3 , tiie loweat num- ber of trials (14) was made by a rut whose total distance was ne>.t to the lowest, but whose time record v.as higher than that of one rat finishing at sixteen trials and those of tvvo rats finishing at thirty-eight trials each. The greatest number of trials (84) was made by a rat whose time record was exceeded by eighteen others, while its distance record was exceeded by four others. The lowest time record as well as the lowest distance record was made by a rat which finished in sixteen trials, the highest time record by one requiring twenty-four trials, whose distance record was an average one. The highest distance record belongs to the rat with next to the highest number of trials whose time is also next to the greatest. Group averages were; Time Trials Absolute Total Distance Speed 41 11.6 sec. 743 min. 367.5 m. 8.2 cm. per second The apex of the trial curve (Pig. 6-A) lies at twenty-eight, although the average is forty-one. The large number of rats finishing after thirty trials however easily accounts for the apparent discrepancy. Two maxima are found in the time curve, (Pig. 6-B), at seveiiteen hundred and twenty-eight hundred re- spectively, but again the general average is raised by the twelve 46 TABLE V - 300 DAY lOTS. 13 males - 15 female s Kat Trials Trial Itev. Time (sees] Time var. Distance (cmj Diet. Var. Absolute T ~d^~' 5 29 12 8221.0 3759.7 30962.8 5792.1 12.7 17 48 - 7 1943.8 2517.5 35558.4 1196.5 9.5 22 82 -41 1222U.6 -7759.3 72300.4 . -35545.5 14.5 24 42 -11 5605.8 -1144.5 43411.2 6656.3 13.5 25 54 -13 1862.4 2598.9 33017.6 3737.3 10.2 26 19 22 8937.2 -4475.9 33760.0 2994.9 11.3 30 27 14 3167.4 1293.9 19980.8 16774.1 13.1 33 16 -25 956.4 3501.9 11731.2 25023.7 19.5 34 66 -25 2899.0 1562.3 55929.6 19174.7 10.7 36 26 -15 2618.4 1842.9 24358.4 12396.5 8.6 37 44 - 3 2861.2 1600.1 33068.8 3686.1 13.0 38 34 7 1706.6 2754.7 26793.6 7961.3 6.5 39 35 6 4227.2 234.1 35916.8 838.1 6.9 ■ 1 20 21 11113.2 -6651.9 31609.6 5145.3 35.2 2 62 -21 4745.6 - 284.3 56636.4 -19881.5 5.8 9 25 16 7029.6 -2568.3 34898.6 1856.3 9.0 12 24 17 13639.6 -9178.3 32563.0 4191.9 7.4 14 19 ZZ 432U.6 139.7 26163.2 10591.7 21.4 15 78 -37 2646.4 1814.9 50601.8 -13846.9 11.5 16 20 21 1640.2 2621.1 18227.2 18527.7 14.3 18 40 1 2431.4 2029.9 42406.4 5651.5 6.6 19 14 27 1598.4 2862.9 15059.2 21695.7 13.0 2U 58 -17 4614.9 - 153.6 66342.4 -29587.6 15 .-5 21 30 11 1682.6 2778.7 26035.2 10719.7 8.3 27 70 -29 7567.6 -3106.3 60960.0 -24205.1 6.2 28 38 3 1134.0 3327.3 24652.8 121U2.1 6.2 31 84 -43 2087.0 2374.3 56115.2 19360.3 8.3 35 38 3 1438.4 3022.9 28076.8 8678.1 6.7 Totals 1142 480 124916.5 78163.1 1029137.4 347818.4 325.4 Averages 40.7 17 4461.3 2797.2 36754.9 12422.1 11.6 Av. for d' 40.4 15 4402.0 2696.0 34437.6 10905.8 11.5 " " ? 41.3 19 4512.6 2874.3 38U23.1 13736.0 11.7 THREE HONORED DAY HATS 47 DNIT - 1 10 20 30 40 50 60 70 80 90 100 NUMBER OP TRIALS DNIT = 10 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1 TOTAL TIMS (SECONDS) DNIT = 100 100 200 300 400 500 600 700 300 900 1000 TOTAL DISTANCE ( CENTIMETERS) 48 animals who required more than three thousand seconds in which to learn the maze pathway. There is a decided apex in the dis- tance curve (Fig. 6-G) at thirty-three thout^and, which nearly corresponds with the group average of thirty-six thousand. Average mean variations for the group were: Trials 41 ±17 41,% Time 745 ri:in. ±466. min 63^^ Distance 367.5 m. ± 12^.^ m 365^ Once more the distance variation ia seen to be the least. There was almost no difference between the learning of the males and that of the females, such difference being even less marked than in the twenty-five day group. The averages are : Trials Time Absolute Total Distance Males Females. . ..40 ..41 11.5 sec. 11.7 " 733 min. 752 " 344.8 m. 380.2 " Both time and distance variation for the males were less than for the females. Time Variation Distance Variation Kales 449 min. 109 m. Females 479 " 137.3 ra. ?ive Hundred Day Rata. Records on only ten rata h&ve been obtained in thi3 group, six strains being represented by four malea and uix femalea who began the problem when five hundred days old. These rata lixe the 300-day animals were fed in the maze for ten days previous to the commencement of the problem, and allowei to eat for from six to eif^ht minutes at the clone of each days work on account of their age. Little differeace in behavior was noted between them and the three hundred day animals. CF i.2/n BE ^/s/m CP V^//^ BH %^-/n V.^ '^/t/^ EJ ''/"//^ Total 0 0 10 3 0 4 112 10 1 6 All 1 1 3 1 5 1 10 Too few rats have been used to make this group really com- parable with the rest, but averages and totals are nevertheless shown. Trials varied in number from eighteen to fifty-six, ab- solute time from five and four tenths seconds to seventeen and eight tenths seconds, total tine from one hundred and sixty-seven minutes to eleven hundred and sixty-seven minutes, and total distance from one hundred seventy-tv.o and eight tenths meters to six hujidred forty-one and six tenths meters. Again there is no relation apparent between trials and time or distance, and total time and total distance do not bear a pro- portional relation to each other. (Table VI) The rat which finished in the fewest trials (18} had next to the highest time TABLE VI - 500 BAY RATS. 50 4 males - 6 females hat Trials Trial Dev. Time I sees J Time Var. Distance Dist.Var. Absolute Icm) T 1994.0 20922.2 12666.4 16.2 -3678.2 42167.8 -8579.2 7.6 -2696.0 17280.0 16S08.6 17.8 448.2 64167.4 -30578.8 5.4 cP 6 32 6 1331.8 9 43 - 5 7004.0 10 18 20 6021.8 11 56 -18 2877.6 9 1 47 - 9 2 34 4 3 45 - 7 4 38 0 7 32 6 14 30 8 totals 375 83 Averages 38 8.3 3117.3 208,5 41450.4 - 8159.0 13.2 1570.2 1755.6 27381.6 5909.8 9.4 3763.8 - 438.0 37791.2 - 4499.8 10.5 3124.2 201.6 30559.6 2731.8 7.5 1005.2 2320.6 2U577.0 12714.4 8.7 3443.0 - 117.2 30616.8 2674.6 11.7 33268.9 13857.9 332914.0 104822.4 108.0 3325.9 1385.8 33291.4 10482.2 10.8 Av. for £^38 12.0 Av. for 36$; 56 age except for the 65-day grouj, where again the loT/ering of the average is due to the aui-eriority of males over those of the 25 day group, the females being auj-ericr in the 25 day grou; As compared with the 65 day grouj . The difference between the two younger groups a id the two older ones is not so marked as that for trials or time but it in nevertheless apparent that the mem- bers of tlie latter covered more ground than those of the former. Yerkes found his older dancers somewhat superior to the younrer ones in learning the labyrinth. The writer finds that the young- er rats learn the maze in fewer trials, that their absolute time is leso , their total time and distance are less, and that their speed is greater than in the case of the older rats. His ten month dancers were superior to those of one to two months while the 25 and 65 day rats of this experiment formed the maze habit more quickly than those 300 days old. The si,eed (which it will be remembered is the average number of centimeters run per second throughout the learning process, no distinction being made between early and late trials] without exception decreases with increased age. The last group is distinctly slower than any other and this to our mind is again proof of the lessening of activity with age. The absolute time, which we have taken as the indication of final efficiency, also diminishes with increasing age, and is considerably lower at 300 days than at any previous age. Thus, while at 2r days the average length of time required for the execution of a peri^ect run was 5.7 seconds, at 300 days the very best tine in which the food could be reached was 11.6 seconds, more than twice the time of the youngest group. It follows that 57 in the formation of habits in which the factor of speed is of an importance equal to or greater than that of exactuess, the older animals would be considerably handicajped. In the field of ani:T^al experimentation illustrations of habits where speed is an important factor are difficult to find. On the human side such an illustration might be had in the acquiring of tech- nique in piano playing or voice culture, either of which de- mands the rapid succession of the muscular activities involved in rendering scales, arpeggios, trills, etc. It would seem that habits requiring extreme rapidity of excession within a jre- ^ scribed rthym could not be learned by the older animals. A comparison of the relation of distance to time in the younger and older groups is interesting. In the first two groui 8 the distance is relatively high showing the excess ac- tivity displayed by the younger animals, in the 200-day group it is about the same as the time, indicating that excess activ- ity is at a minimum, while in the last group it is much less than the time, showing that the effects of old age have begun to manifest themselves through a general slowing up of activity. If the distance alone be taken as a measure of activity, our results agree with those of Slonaker who found the most ac- tive age to be between ten and twelve and a half months, since our 300-day rats covered more distance in learning the problem than any other group. If, however, distance be considered in relation to time, the older rats a] pear much less active t}ian the younger ones, as is shown by the average high speed attain- 68 el by the young in comparison with the old. Certainly the be- havior of the old animals wlien in the maze is much more deliber- ate than that of the young ones, and the writer beliuvea that if SlonaJcer had possessed some means of measuring the amount of activity per unit of time he would have found the young far more active than the old. In Table VIII is given the average speed for each group for the 1st, 2nd and ICth trials, the tv;o trials immediately preceding the last six, and the last six trials. The increase of speed from the first to the 2nd trial is considerable except in the 200-day group where there is a decided decrease. The gain from the 2nd to the 10th trial is great except for the 3C0-day group where it is comiaratively small. From the tenth trial to the two preceding the last six the gain for the 200 and SCO-day groups is greater than for the 25 or 65-day groups, and from these two trials to the last six trials the gain is again greater for the 200-day rats. This gives a slight indi- cation as to where the most rapid learning occurs. A full set of tables showing the speed for every trial of each grouj would be necessary for an adequate discussion of the question, but from the present incomplete data it appears that the learning in the two younger groups is most rapid during the early stages, while for the older groups it is more rapid during the later trials. Especially is this true of the 300-day group, the in- crease in speed being very gradual during the first ten trials then more than doubling from the tenth to tl:e two immediately preceiing the last six. In general, speed, for the separate trials tabulated, decreased with age which accords with our 59 observation on the average speed for each groui during the en- tire jieriod of formation of the maze habit. TABLL VIII jpeed - (cm. per sec) Age l3t Trial 2nd Trial 10th Trial 2 preced- Last ing last 3ix six 25 days 7.8 9.8 52.0 74.2 90.0 65 7.2 11.1 35.0 52.0 75.0 200 8.3 4.7 21.0 40.7 56.2 300 3.0 4.2 5.5 20.8 40.9 IHCIDEIITAIi TESTS. Although the primary object of this investigation was to determine the relation of age to rapidity of habit formation, several minor points of interest have been touched upon in the course of the experimentation which it may be well to mention. Effect of Sex on Rapidity of Learning. The ideal way in which to test this matter would be to have an equal number of males and females from each litter used, and at least twenty animals of each sex used at each age. In our vork this was impossible, but the averages given in Table IX are in no instance based on less than eleven animals. 60 the number in each case being given, TABLE IX. Time Ape Trials Absolute Total Distance Speed (11 Males 32 25 Days) fl6 Females 29 5.7 sees. 215 min. 277.1 m. 21.6 cm. per sei 5.6 232 " 26 7.8 " 19.2 " (16 Males 27 65 Days) (11 Females 37 7.1 6.3 192 257 228.3 " 19.8 307.6 " 19.9 (15 Males 39 9.7 200 Days) (13 Females 45 7.2 263 " 465 " 296.3 " 19.5 " " " 388.4 " 13.8 " " " (13 Hales 40 11.5 300 Days) (15 Females 41 11.7 734 " 752 " 344.3 " 380.2 " .2 " (55 Males 35 8.2 Gen.Av. ) (55 Females 38 7.7 351 •' 427 " 286.5 " 17.2 336.0 " 15.3 MEAN VARIATION Total Time :otal Distance ( 25 days) ( 65 Day8( ) 200 Days( ) 300 Day3( ) Gen. Av.( ) 96 rain. 146 " 103 " 107 " 169 " 173 " 449 " 479 " 208 " 224 " 79.6 52.4 72.7 96.5 171.8 130.6 109.0 137.3 108.2 104.2 61 It maye be seen from the table that the males are at every age aonev'hat suj-erior to the females in learning ability, their superiority being less marked in the young and old grou^-s (25 and 300 days) than in the two intermediate groups (65 and 200 days). The general averages for an equal number of males and. females shov; the males Bujerior to the females in all points save one, that of absolute time. They finished in fewer trials, required less total time, and covered a smaller amount of dis- tance in learning the problem than did the females, while their speed was slightly higher. This conclusion is at variance with that of Yerkes regarding the dancer, he having found the females snperior to the males in learning the laoyrinxn. In the matter of final efficiency as evinced by the absolute time, the females are superior to the males at all ages except three hundred days when the tv«o records are practically equal. The general aver- age shows this to be the one point wherein the record for the females is better than that for the males. The mean variation from the time average is leas for the males at all ages, their distance variation is less at sixty-five and three hundred days. The general average shows the smallest time variation for the males and the smallest diotance varia- tion for the females. These results do not agree with those of Yerkes on the dancer. His ten month fSOO day) dancers learned the labyrinth more rabidly, the number of trials required being the measure of learxiing, than those one to two months oli (30-60 days) while there was no difference in the learning ability of the females at the two ages. My 25 and 6£ day rats of both sexes formed the maze habit considerably more rapidly than the 300 day animals. The fact that in the number of trials, total time and total distance required to learn the problem, the males at 65 days are superior to those at 25 days while the reverse is true of the females, sugp;ests the possibility that the capacity for habit formation develops earlier in the females than in the males. Day and Iflght Work. It has been stated by Slonaker and is generally believed that the albino rat is nocturnal. With a view to testing this matter certain rats in the twenty-five and two hundred day groups were run always in the day time, certain others always at night. The averages for the day and night rats were obtained in the same manner as the group averages, from Tables A and C. The twenty-five day rats run during the day were numbers 1,2,4,5,6,15,16,17,19,20,21 and 24, seven of which were males and six females. Those run at night were numbers 8,9,10,11,12, 13 and 14, two males and five females. The averages which ap- pear below in Table 1 seem to show the day rats slightly super- ior in distance and trials while the night rats consumed less time and had a slightly higher final efficieiicy. These differ- ences are negligible, and there may be said to be no difference in learning at this age between the rats run in the day time and those run at night. The day grouj of two hundred day rats consisted of two males and four females numbers IB, 1^,20,21,23 and 24, while the night group included tv.o malea and four females numbered 6,7,8,'^ 10,15 and 17. The averages ahow the night grou] to be superior to the day grouj in every respect save that of final efficiency. Mevertheless, we are inclined to hold to our previous statement that no difference is shov.'n in learning ability, for the follov/- ing reason^ the general average for the females of this group was considerably higher than that for the males exoeit in the matter of absolute time. In the day group there were only two males and four females. Were the number of males the same as the number of females it is our belief that the average would be considerably lowered and the day and night grouj^s prove to have practically the same ability in learning the maze problem. TABLE X. AVERAGES Time Trials Absolute Total Distance 25 days: Day ES 5.5 sec. 207 min. 247.4 meters Night 31 5.4 " 159 " 261.6 200 days: Day 41 6.2 " 461 " 373.5 Night 34 7.2 " 325 " 267.9 Continuation of V/ork after the Problem has been Learned. Another question which interested us was, what would be 64 the effect on efficiency if rata which had learned the problem were caiiaed to continue their runs in the maze for a long period i.e., would continued i^ractise cause a marked increase in effi- ciency evinced by a lowering of the absolute time rocord, or had the highest possible level already been reached in the last six trials of the learning process? To test the matter six tats of the sixty-five day group were kept at work for more than one hundred sixty trials after learning was complete, the average time for each six trials was computed and appears in Table XI as twenty-seven tests. Taken individually the results show that in every case a lower record than the absolute time record was made, but in no case maintain- ed. If the group average be noted, the absolute time is never quite reached, the curve (Fig. 8) starting a little above it and continually rising. In other words, final efficiency de- creases rather than increases when practice is continued, ^n interesting point is that errors will be made even after the problem is learned. Of the six rats used, three made errors in the first test of six trials after the problem was learned, one in the second test, and one not until the fifth test. Lrrors increased as the work was continued. During the last half of the one hundred sixty additional trials twice as many errors were made as in the first half. A closer examination of the table shows: Ist, that the best record in each case was made during the first fourteen testa; 2nd, that the last test was better than the first in only one case (rat 15]; 3rd, that rats fourteen and fifteen "' : Rat 8 Rat 12 Eat 14 Rat 15 l^t 16 Rat ; 17 Ab. T. 6.6 6.4 5^ li5 5^ 4.3 ^ 1 6.7 7.1 6.5 ee 5.1 5.3 e* 2 6.4 ^ 7.e 5.3 e^ 4.8 11 4.7 * 4.5 3 5.4 i^ 7.9 ee 4.8 i 4.8 6.9 e 6.3 6 4 5.2 :): 9.4 ee 6.1 e 4.1 * 9.1 6.0 e 5 6.7 e 17.6 eee 5.8 # 4.6 # 6.1 5.1 6 5.8 8.5 5.1 # 4.9 # 8.8 10.8 ee 7 7.2 e 6.8 5.8 7.8 6.2 4.8 ee 8 5.3 V 5.4 e * 5.0 e# 5.4 # 7.9 e 4.7 9 5.5 e# 6.4 5.0 # 6.4 e 6.1 4.3 # 10 8.2 eee 5.4 :i: 5.8 # 4.3 # 14.6 eeee 4. 4.7 11 5.2 * 6.1 e ^ 5.5 '> 14.3 0 5.6 e 6.6 e 12 6.9 eeeee 5.5 jt 4.6 $ 4.7 # 6.5 e 4.9 e 13 6.7 e 5.7 e ^ 4.8 i 8.2 e 6.9 e 4.4 # 14 21.5 eee 7.2 e 5.2 # 8.1 6.2 4.7 Errors ~ ~ 15 13 5 5 9 8 ■ 15 6.8 ee 8.8 4.9 e ^ 5.0 // 5.1 ^ 4.7 16 10.0 eee 6.7 e 5.7 19.3 ee 8.4 5.4 17 14.1 eeee 6.2 ^ 4.7 e ^ 5.6 e 8.2 ee 5.1 18 6.9 ee 5.7 # 5.4 ^ 5.1 $ 6.7 4.8 19 10.3 ee 9.9 5.2 # 5.5 7.3 5.4 20 5.9 e ^ 12.2 5.2 # 5.1 i 5.7 4.5 21 19.0 eeeee 7.5 5.8 # 7.7 22.0 e 8.6 ee 22 11.4 eeeee 9.3 e 8.8 5.6 24.3 eeee 7.6 eeee 23 6.5 e ^' 7.9 e 5.7 e# 12.2 14.5 e 19.9 eeee 24 10.1 eee 9.8 eee 6.4 7.1 16.1 eeeee 6.6 e 25 6.9 ee 12.9 f 6.0 5.4 # 8.9 e 5.4 26 11.5 eeeee 6.0 5.4 e# 5.7 10.4 e 6.7 e 27 16.6 ee 8.8 ee 7.1 5.7 15.9 eeeeee 5.1 28 8.1 7.5 6.8 e 5.0 $ 18.8 eeee 6.2 29 9.3 ee 30 7.8 Errors ~ 37 10 5 3 27 12 8 = Error * = lowest record for individual rats # = lower record than absolute time value for certain rat. The dotted line divides the table into first and second halves in order to maJno compariBon of the two stages easier. The number of errors made by each rat in each half is shown. 15 10 Sig. 8 BPPECT 0? rSIAL. CONTINUATIOt^ ON TIME SPPICISNCY 0? SIX SIXTY-PIVS DAY RATS o 10 15 20 25 27 TESTS Each point on the curve rsprsssnts bhs average for 16 trials 167 trials shown here as 27 The asterisk (*) indicates the point of efficiency which had been reached in the learning proper, i.£,,the last six trials of learning. 87 probably had not reached their efficiency level during the learning irocesi', while the other rata had. This fact ia deduced from the number of times each rat male a record low. er than its absolute time record. Rat 8 9 times out of 28 " 12 8 "14 21 "15 14 "16 2 " 17 3 " " Blood Relationahip and Learning. It was found that the learning ability of certain inerbera of a groui could be predicted from the results obtained on other nembera of the same litter. The data appear in Table XII. Three rats from the YfC?) litter v/ere used when twenty-five lays old, and five rats fron the sane litter worked when sij.ty-five daj'S old. Two members of tlie G J litter learned the problem at twenty-five days, and one at sixty -five days. Two A L rats worked when twenty-five days old, and one when sixty-five days old. ?our X L rats learned the problem at twenty-five days, three at sixty-five days and three at two hundred days. The rats belonging to the YfC^) litter required a smaller number of trials at 25 days than the average, but their absolute time, total time and total distance were above the average for rats of that age. At 65 days, rats of the same litter made averaj^eo higher than the group averages for that age exce^ t for the absolute time. The GJ rats twenty-five days old had a trial and distance record higher than that of the entire group while their absolute and total time was less. The same holds true for the GJ rets at 65 days except that their absolute time is higher. AT. rats show records lovver than the grorp averages in every case at 25 days but at 65 days all of the AL averages are higher than that for the group. iiats from the XL litter which worked at 25 days made low- er records than the average except in absolute time. The same is true of the 65 day members of the same litter and the 2C0 day 69 XL rats have a lower record than tlie groui. average in every i,ar- ticular. In tliree out of four cases consilored then, a high or low average at one age seems to indicate whether there will be a high or low average for the age or ages following: It appears that it is possible within limits to predict the capacity for habit formation of .rats of a certain litter at a given age, from the behavior of their blood relations at any other age. TABLE ill. Time Trials Absolute Total Litter Age Distance YCF (25 days )65 " (200 " 25 40 5, 5. ,9 .9 sec. 463 317 min. 290, 369, .1 .4 meters n GJ (25 days (65 " )200 " (25 days )65 days (200 " (25 days )65 " (200 " 35 38 5. 7, .3 .6 n 140 136 n 319, 284, .3 .0 11 AL 23 38 5. 10. ,4 .6 „ 91 330 IT 185, 393, .8 .2 " XL 34 24 29 5, 8, 1, ,4 ,3 ,8 »» 180 153 258 t1 252, IV 5. 254. .5 .3 .4 n (25 days Gen.Av.)65 " (200 " 30 31 42 5. 6. 8. ,7 .8 ,6 " 224 318 3£1 t1 271, 260. 339, .6 .6 .1 n 70 Retention. A retention test was male on five indiviiuala of the 65 day group v\ho were caused to relearn the problem after 90 days. Durin/T this time they were fed daily in the maze except that at the 85th day the food supply was cut down, and on the 89th day no food at all was allowed. Probably a better plan would have been to feed the rats in the food box of the mare for a week preceding the retention test, usinp the same schedule employed in preliminary feeding, and keeping the food box carefully parti- tioiied off from the rest of the maze. Seventy-six percent of the original number of trials were required to relearn, forty-eight percent of the time nec- essary for learning was occupied in relearning, and fifty-two percent of the original amount of distance was covered. The absolute time when learning was 7.9 seconds, when relearning 9 seconds, this difference probably being due to the increas- ed age, since the rats were approximately 200 days old at the time of the retention test and absolute time increases with age. Nothing more is shown by the test on retention than that the interval between learning and relearning must be made very much smaller if it is desired to begin a problem v/ith a view to determining the curve of retention. The relation of time to distance in learning, and the matter of elimination of alleys in the maze have been discussed at length in papers already published. TABLi. XIII. Learning 71 Hat Trials Ab. Tin.e Total Time Diatanoe 1 30 8.2 sec. 1327.4 sec. 23033.6 cm. 2 54 7.8 " 1651.8 sec. 42360.0 " 3 21 7.1 " 1542.0 " 25177.6 " 4 16 S.8 " 496.0 n 11603.2 " 5 2E 6.5 If 2378.0 " 26675.2 " Totals 143 39.5 " 7395.2 " 128857.6 " Averages 29 7.9 " 1479.1 " 25771.5 " Relearning (after 90 days Ab. Time Total Time Rat Trials Distance 1 14 7.7 sec. 316.4 sec. 7264.0 cm. 2 40 8.7 " 861.8 " 23321.6 " 3 14 9.2 n 484.4 It 9081.6 " 4 22 10.3 " 958.8 ■' 15562.6 " 5 18 9.3 " 902.6 " 11426.8 " Totals 108 45.2 n 3524.0 t» 66656.6 " Averages 22 9.0 " 704.8 " 13331.3 " 72 RESUME OF C0NCLU3I0:i3. 1. Youn£- rats learn the maze more rapidly than the oil ones, the rapidity with which the habit may be formed decreasi.ig with increase in age. 2. Absolute time, the time required for the execution of the perfect run, increases with increase in age, the oldest group requiring more than twice as much time as the youngest. 5. The most rapid stage of habit formation occurs ear- lier in the learning process of the younger animals than of the older ones. 4. In the very young rats (25 days )and the very old (300 days) sex differences are negligible, while among the ani- mals of medium age (65 - 200 days) the males learned more rapid- ly than the females. 5. In general, the absolute time for the females is low- er than that for the males suggesting greater efficiency on the part of the former in the execution of the habit v.hen it had once been perfected. 6. Practically no difference in ability to form the maze habit is to be found between rats learning the problem in the day time and those learning at night. 2* Continue! practice after the problem has been learn- ed causes a break in the habit and does not result in an in- crease of final efficiency. 8. The rapidity with which the maze habit will be form- ed is predictable within certain limits from one family group 73 to another. 9. Tn the matter of elimination of errors, the outer alleys are usually those in which useless movements are last to drop out, but a 5-4-;.-2 order does not holl, i.e., errors in 5 dro],ping out first, those in 4 second, etc. This bears directly on the question of the relation of the food to the learning process and seems to negate the pleasure-j^ain hyjo- thfisls, but no conclusive evidence has been obtained. 10. The importance of an adequate test on retention is made quite evident by these results. If an analogy may be drawn between the learning ability of the rat and that of the human subject, it may be seen that in general the old can lear i a given problem as well as the young although more effort is required to do so. The efficien- cy of this learning can only be measured by testing the reten- tion ability. Should such tests show that the old animals forget very rapidly and must relearn the problem continually with little or no lessening of excess effort, comparing ujifavor- ably vith the younger ones in these respect, the above conclu- siont: would have to be modified. If, however, the limits of retention in the groups are fou.id to be very nearly the same, and the amount of effort necessary to relearn not greatly in- creased for the older group over that for the younger, the de- ductions would hold. 74 BIOGRAPHY. Helen B. Hubbert, the author of this diaaertaticn was born at Lincoln, Illinois, June 11th, 1887. Eer early edu- cation was received at the Preparatory Department of Cumber- land University and in the Academy of F.iasouri Valley College. In 1904 she entered Missouri Valley College, Marshall, luissouri, from which she graduated in 190 7 with the A.B. de- gree. In 1907-1908 she was a graduate student at the Univer- sity of lennsylvania. In 1908-9 she attended the Clarke Train- ing ochool for Teachers, and from 1909 to 1912 was a teacher in the Pennsylvania Institution for the Deaf at Lt. Airy, Philadelphia, la. In the fall of 1912 she entered The Johns Eopkina University as a graduate student in Psychology, with Physiology and Paychopathology as subordinate subjects. She received a university scholarship in 1912-13, was Fellov; in Psychology in 1915-14, and held the tellowshii of the I3alti- more Association to promote the university Education of 7/omen in 19i;-15. .mm^