ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR REPORT NO. 3 PSYCHO-MOTOR EFFICIENCY (AS MEASURED BY TIME FOR ACCURATE GUN-LAYING) UNDER HOT CONDITIONS By DOUGLAS H. K. LEE G.H. KLEMM C. WHITE Project 2167 DETROIT ORDNANCE DISTRICT, DEPARTMENT OF THE ARMY CONTRACT DA-20-018-ORD-13146 April, 1954

NOTE This paper was prepared by Dr. Douglas H. K. Lee, now Professor of Physiological Climatology at the Johns Hopkins University, while he was associated with the University of Queensland in Australia. Because of the importance of the paper to Engineering Research Institute Project No. 2167, the Engineering Research Institute of the University of Michigan undertook reproduction for limited distribution. This was done with the permission of Dr. Lee. Project No. 2167 is sponsored by the Detroit Ordnance District, Department of the Army, under Contract No. DA-20-018-ORD-13146.

TABLE OF CONTENTS Page LIST OF TABLES iii 1. APPARATUS 1 1.1. Gun-sight Unit 2 1.2. Target Unit 2 1.3. Recording Unit 3 1,4. Control Units4 1.5. Circuit 4 1.6. Operation 5 2. PLAN OF EXPERIMENT 6 3. EFFECT OF REPETITION 8 4. EFFECT OF HEAT ALONE 9 5. EFFECT OF EXERCISE IN HEAT 10 6. EFFECT OF NOISE IN HEAT 10 7. EFFECT OF LACK OF SLEEP IN HEAT 11 8. EFFECT OF MEALS IN HEAT 11 9. EFFECT OF RESPIRATORS 12 10. COMPARISON OF PHYSICAL WITH PSYCHO-MOTOR REACTIONS 12 11. CONCLUSIONS AND PRACTICAL APPLICATIONS 13 11.1. Conclusions 13 11.2. Applications 14 12. FURTHER WORK REQUIRED 16 13. ACKNOWLEDGMENTS 16 PREVIOUS REPORTS 17 ii

LIST OF TABLES Table Table Table Table Table I II III IV V - Schedule of Experiments in Series T/9 - Schedule of Experiments in Series M/1 - Effect of Repetition upon Gun-Laying Reaction Times - Effect; of Heat Alone upon Gun-Laying Reaction Times - Effect of Exercise upon Gun-Laying Reaction Times in Heat - Effect of Noise upon Gun-Laying Reaction Times in Heat - Effect of Lack of Sleep upon Gun-Laying Reaction Times in Heat - Effect of Meals upon Gun-Laying Reaction Times in Heat - Effect of Respirators upon Gun-Laying Reaction Times - Comparison of Physical with Psycho-Motor Reactions Page 18 19 20 21 Table IV Table VII Table VUII Table IX Table X 25 26 27 28 iii

REPORT NO. 3 PSYCHO-MOTOR EFFICIENCY (AS MEASURED BY TIME FOR ACCURATE GUN-LAYING) UNDER HOT CONDITIONS Everyone who has attempted to investigate fatigue has met the problem of measuring mental as opposed to physical deterioration. The range of tests devised for this purpose is very large - in itself a testimony to the unsatisfactory results obtained. The two main drawbacks to these tests are lack of motivation and difficulty of interpretation. The time of onset and degree of mental fatigue developed are matters of importance in most military operations. To deal with military aspects and at the same time to minimize the drawbacks mentioned above, we endeavored to design a test which would appeal to the majority of service personnel as being something "practical", and permit of fairly direct application to military problems. The only material available when the investigation was started was that to be found in a routine teaching laboratory. Radio valves, galvanometers and electric meters were unobtainable. More specialized equipment is gradually becoming available, but at the time improvisation was the only way through. Fortunately, we possessed a fairly well equipped workshop. The test adopted consisted essentially of measuring the speed with which a gunner laid and fired at a target suddenly appearing at an unknown spot on a landscape. l. APPARATUS A description has already been given (AFV 50 and 30a) of the basic apparatus under the title of "Efficiency Tester - Gtin-laying Type No. 1". This essentially recorded the time taken to lay accurately upon the target, i.e., it answered the question "What time is required for accurate shooting?" Since then, the apparatus has been improved and additions made which permit an examination of the approach to the target as well, so that the complementary question can be answered, "What degree of accuracy is possible in a given time?" 1

2 For convenience, a complete description will be given here of the latest apparatus. In the section describing results, an indication will be given when the original apparatus was used. 1.1. Gun-sight Unit (Fig. 1, Diag. 1) A "gun-sight", consisting of a stepped tube, pinhole ocular and plain glass objective with cross-wires attached, is mounted on traverse and elevation gears (from standard Mecanno parts 25a, 27b and 29) actuated by handles. A reversible eyeshield is mounted near the ocular. Geared to the traverse mechanism is a rotor arm carrying two contacts, the inner one of which (TA) rides over a horizontal ebonite plate bearing six small contacts, and the outer one (TB) over a closely wound resistance coil (28 swg nichrome wire) mounted on the circumference of the ebonite plate and at right angles to its plane. The inner contact has a needle point, the outer a ball point, both spring loaded. The arm is mounted on the spindle by means of an insulating fibre block and retained in position by a clamping screw. The outer contact is insulated from the inner by a bakelite section. A similar arrangement is geared to the elevation mechanism. There are thirty-six positions in which the inner rotor arm points TA and EA will each be in contact with one of the plate contacts, and thus be able to complete a signal circuit ("pinpoint" circuit). In between these positions, the outer rotor arm points TB and EB mark off distances from these positions along the resistance coils, and thus allow their position to be recorded by the varying potentials led off ("approach" circuit). The whole of this mechanism is mounted on a standard with a heavy base. A trigger is mounted on the standard, and incorporated in the "pinpoint" circuit. A total pressure of 2-1/2 lbs is required to establish contact. A levelling bubble is mounted on the traversing support at right angles to the axis of sight. The base is screwed to the floor in such a way that the bubble remains centered in all traverse firing positions. Contacts are also mounted on the two main gear wheels and the two ebonite plates in such a way that a separate circuit is completed with the gun-sight is in a central (neutral) position. 1.2. Target Unit (Fig. 3) When the gun-sight unit is built, the target unit can be made. A plywood board 6 feet square and suitably braced is set up vertically at 12 feet from the gun-sight unit and at right angles to its center line of sight. The positions of 36 targets are mapped out by "spotting".

3 To do this the gun-sight is first pointed at a spot approximately 9 inches away from the center of the board towards one corner. The rotor arms are then adjusted until the needle contact points are just in the centers of the small plate contacts appropriate to this position, and the clamping screws tightened. A lighted bulb is now moved about on the target board by an assistant until it is seen in the center of the sight. The position of the bulb is marked. The sight is now moved by the elevation and traverse handles until the needle contact points are centered in another pair of plate contacts, and the position on the board again determined and marked. This procedure is continued until all 36 positions have been determined. (It is essential, of course, that the initial settings of the rotor arms on the spindles remain undisturbed throughout.) Holes of 1-inch diameter and centered on the marks are now cut in the board and a 3.5 volt torch bulb mounted centrally behind each. The board is now thoroughly painted to minimize water exchange with the atmosphere. A landscape is painted on the board itself, or on sisalkraft tacked on. 36 sisalkraft discs of 2-1/2-inch diameter, each with a central aperture of 1/2-inch diameter, are made, and the apertures covered with thin white paper. Each disc is painted to harmonize with the landscape round the hole pinned over it, so that its aperture is centered on the crosswires when the rotor arm points are centered on the plate points, as judged by a further process of "spotting". Fixed even illumination of medium intensity, such as that provided by two 60 watt lamps with bright tin reflectors 5 feet from the target, is required for comparative work. One-sided daylight is excluded. 1.3. Recording Unit (Fig. 2) In the original apparatus, ink-writing magnetic signals were used. In the later type, continuous records are required of potential variations. As neither ink-writing galvanometers nor optical recording apparatus were available, we fell back upon the classical smoked paper method of recording. Magnetic signals are used to record the switching on of the target light and the successful firing of the "pin-point" circuit. The potential variations produced by the movement of the rotor arm over the resistance coils of the "approach" circuit actuate two D'arsonval type galvanometers. The recording arm of each is fitted with a Sherrington writing-point made of aluminum wire. Care has to be taken in all three planes to get the magnetic signals and the galvanometer writing points properly aligned. Strips of smoked paper 100 cm x 40 cm are used. The drum is driven by an external a.c. induction motor. This has been found to reduce error to less than 5% in a single measurement and less than 1% in the mean of 20 measurements. The paper is kept taut under the writing points by an adjustable roller. To facilitate alignment and the removal of records without marking, the counter-pulley is mounted to swing horizontally.

4 1.4. Control Units The first (Control Unit I) is a panel of 36 double-circuit switches, arranged in ranks and files on the square, each corresponding to one target and controlling simultaneously the switching on of the target light and the pre-selection of the two plate contacts corresponding to that target. Also mounted on this panel is a light to indicate when the gun-sight has been returned to the neutral position. The second (Control Unit II) consists of a pair of rotary switches for separately pre-selecting the appropriate sections of the elevation and traverse resistance coils. 1.5. Circuit (Diags. 2 and 3) There are five basic circuits, which may be described separately. (a) Target Circuit. One half of each double-circuit switch on Control Unit I links one pole of a 4-volt cell to the filament of a target light. The target light filaments are connected in common through a magnetic signal to the other pole of the cell, (b) Pin-point Circuit. One pole of the same 4-volt cell is connected to the traverse rotor arm. Each traverse plate contact is connected to one side of the second half of each double-circuit switch on Control Unit I which lies in the appropriate vertical file. The other side of each switch is connected, with its fellows of the same horizontal rank, to the corresponding elevation plate contact. The elevation rotor arm is connected to the other pole of the cell through successively, the firing key, a bell, and a magnetic signal. The circuit can be completed only when the inner rotor arm contacts are in apposition with the plate contacts corresponding to the target light switched on. (c) and (d) Approach Circuits. The elevation and traverse circuits are similar and operate from separate two-volt cells. In each case one pole of the cell is connected to the arm of the rotary switch in Control Unit II. Each stud of the rotary switch is connected to the resistance coil opposite one of the plate contacts, i.e., in a position corresponding to a target. The other pole of the cell is connected through a balancing resistance to tappings made mid-way between the previous tappings and to the ends of the coil. This pole of the cell is also connected to one of the galvanometers, which is connected in turn to the outer contact of the rotor arm. The galvanometer records the potential drop between the cell tapping and the rotor arm over that section of the coil pre-selected by the rotary switch. This is a maximum with the rotor arm in the target position, a minimum when it is opposite the cell tappingo

5 (e) Neutral Signal Circuit. This is a simple circuit illuminating a light on Control Unit I when the gun-sight is in a central (neutral) position. 1.6. Operation When the gunner is in position, the controller sets the rotary switches of Control Unit II to the numbers indicated the selected target. He then lets in the clutch of the recording drum. When the smoked paper is running steadily, he throws the switch on Control Unit I, corresponding to the selected target. This lights the target lamp and the corresponding magnetic signal makes a mark on the smoked paper. The gunner, on seeing the target light go up, endeavours to lay his gun-sight accurately on the target, as quickly as possible. When he comes within radius of the target, his elevation and traverse movements are recorded by the galvanometers. When he thinks he is accurately "on target" he pulls the trigger. If successful, this will actuate the second magnetic signal and ring the bell. If unsuccessful, he readjusts his sight. When successful, the gunner returns his gun-sight to the central position and the controller reverses the switch on Control Unit I. The drum is then stopped. Before commencing the day's tests and in response to any complaint by the gunner, the controller checks the accuracy of the apparatus and makes any necessary adjustments in the position of the rotor arms. A five second trace is made with the target signal before and after each sequence of targets to measure the paper speed. The record is varnished and dried. The distance between signal marks is measured with a glass rule. The galvanometer records are examined by superimposing a transparent grid of arcs set at 2 mm intervals, As subsequent figures will show, the basic reaction time with the improved apparatus appears to be somewhat less than with the original, but the individual variability seems to be greater. The above explanation may make the apparatus sound complicated, but it is basically simple and should be easily set up if a workshop and suitable material are available. If better gears than Mecanno parts are available they should certainly be used. If available, an integrating device may be used in place of the magnetic signals when individual target records are not required. Ink-writing galvanometers are desirable.

6 2. PLAN OF EXPERIMENT A number of targets (usually 20-25) are selected from the 36 to form a group (indicated by a letter). These are arranged in random order to form a sequence (indicated by a number). The total time taken to sight successfully on all the targets of a given sequence, divided by the number of targets, is the sequence time. This is the basic datum used throughout this report. 4-6 sequences are usually used in succession to give an hour's continuous sighting. Information derived from an examination of the "approach" records will be dealt with in a later report. The usual procedure is for the subject to enter the air-conditioning room after breakfast and remain there for seven hours. The second, fourth and seventh hours are spent in sighting; a standard lunch is taken in the fifth hour; during the first, third and sixth hours the subject sits or performs physical exercise as required. This exercise consists of manipulating "tank controls" against heavy weights or of lifting a heavy weight at a set rate. Free water drinking is allowed throughout. Battle dress KD is worn throughout. The subjects are all well-trained men from the armoured units, most of them with battle experience in the humid tropics. For two or three days before investigations are commenced, they practice on the apparatus. As will be seen later, the learning process is exponential, but this preliminary practice does bring the performance well down the steep part of the curve. Three series of experiments were performed. In Series T/9 the sighting was done from within a "tank" built up in the air-conditioning room from flat panels, which could be electrically heated to simulate a tank standing in the sun and with a hot forward gear-box. The original apparatus was used in this series. In series M/1 and M/2, the sighting was done in the open room, and the improved apparatus was used. In general, subjects are used 4-6 days a week until the series is completed. This maintains acclimatisation and learning, while not actively promoting boredom. It does, however, prevent replacement of a subject who gets sick. All experiments were designed to use four subjects. In certain cases, minor ailments interfered. Where the number fall below three, results have been largely neglected. The following extract from the analysis sheets of Series M/1 will indicate the way in which the basic data of sequence times are treated. All times are expressed in 1/100 secs.

7 Exp. M/la. Standard E.T. 88~F Sequence _Sequence B 1B2 B5 B4 Bi B2 B I B4 BB2 B B4 Subject G13 421 340 396 376 627 475 360 441 448 486 466 456 Subject G14 487 497 525 470 429 440 587 470 505 421 425 430 Subject G15 546 634 570 472 622 690 606 477 618 529 591 492 Subject G16 398 408 386 360 504 408 423 376 420 435 392 423 Within-hour 463 470 469 420 546 503 494 441 498 468 469 450 Sequence Means Within-hour Operation 455 + 13.8 496 + 24.9 471 + 11.5 Means Day Operation Mean 474 + 9.9 In the absence of full analyses of variance, which it has been impractical to make, the standard deviation of the mean of the appropriate sequence means has been used as the measure of variation in each case. This minimizes the effect of between-subject variation whilst retaining the Effect of betweensequence variation and inter-action (see Section 3k). Table I gives a schedule of experiments carried out in Series T/9. Although some controls against learning on the one hand and boredom on the other were provided, the length of time involved was not fully appreciated, so that several experiments (not shown in Table I) were invalidated, and had to be discarded. In drawing up the schedule for Series M/1 (Table II) care was taken, not only to provide controls, but also to arrange the experiments with different subjects so that time factors were offset. The arrangement of Series M/3 is similar to that of M/2 and has been given in detail in a previous report (Fatigue Laboratory Secret Report No. 2).

8 3. EFFECT OF REPETITION In Table III will be seen the effect of repetition upon the reaction time. The following conclusions may be drawn: (a) Within any one day there is frequently an improvement, especially between the second and fourth hour of the test. (b) With repeated test days there is at first an improvement, which assumes the expected exponential form, being rapid at first and gradually falling off thereafter to a minimum. (c) After a certain number of days, depending upon the subjects and conditions used, the reaction time commences to rise again. The process known variously as boredom or mental fatigue makes itself evident. (d) There is a suggestion that the last effect is more prominent under hot than under temperate conditions. (e) The variability of response tends to follow the same curve as the mean reaction times. (These results are largely true, also, of the individual subjects as well as of the averages.) Further interesting information is to be derived from analysis of variance carried out on the results of Experiments M/lr, M/ld, M/lf and M/lfrr with the following results. Sube cts _ Sequences Discrepancy Exp. Period Mean Rao Mean Ratio Mean Ratio Ratio..... Square j Square I Square M/lr 2nd hr 4075 0.65 6034 0.97 6226 (Day 3)* 4th hr 18460 8.21 10841 4.82 2248 7th hr 14658 8.24 3695 2.06 1772 M/ld 2nd hr 50589 19.6 570 0.56 1561 (Day 6) 4th hr 40291 ~974 2267 0.55 4145 7th hr 50480 2 385 0.19 1992 M/lf 2nd hr 49721 54.0 1920 2.09 920 (Day 10.5) 4th hr 49730 2328 1.62 1459 7th hr 52124b 242 0.29 811 M/lfrr 2nd hr 8781 4.80 1630 0.89 1829 (Day 18.25) 4th hr 10051 10.00 1677 1.59 1054 7th hr 9124 5.t 1838 1.31 1404 Double underline indicates less than 1% probability. Single underline less than 5%. *Note that the first two days were practice only. The third day was the first full experimental day.

9 The following observations may be made: (f) The entirely random variation (discrepancy) decreases rapidly during the course of the experiment on the third day, reaches a minimum by the tenth day, but rises again somewhat by the 18th day. (cf. (b) and (c) above). (g) In the 2nd hour on the third day the between-sequency varition is moderately large, but is swamped by the random variation. In the fourth hour it is large, but the drop in random variation makes it probably significant. Thereafter the between-sequence variation remains low and is not significantly different from the discrepancy. (h) In the 2nd hour in the third day the between-subject variation is small, and no greater than the random error. During the rest of the day, however, it is significant. By the tenth day, the between-subject variation is very large. By the 18th day, however, it is considerably reduced and not so highly significant. Inspection of the protocols shows that this is probably due to three of the subjects following a U-shaped, with the fourth following a very protracted learning curve. This large subject variation is the reason for using the SD of the mean of the sequence means as the estimate of variation in operation means, rather than the mean of the individual sequence times. 4. EFFECT OF HEAT ALONE The results of those experiments which permit a comparative survey to be made of the effect of heat alone are given in Table IV. From these the following conclusions can be drawn: (a) Reaction times at effective temperatures of 83.5 and 94~F are significantly longer than those at 65-70~F. The increase is 5-12%. (b) Within the range of effective temperature 88-96~F when the subject is seated at rest throughout the test, the reaction time does not undergo any further increase with rise of temperature, even when physical failure is imminent. (c) Within a similar range of effective temperatures when the subject is doing moderate physical work between tests, the reaction time does undergo a further increase under conditions which bring about physical failure, the additional increase being of the order of 10%. (d) At an effective temperature of 84~F, a hot dry atmosphere results in a reaction time about 11% greater than a hot wet atmosphere, at least in subjects acclimatised to hot wet conditions only.

10 5. EFFECT OF EXERCISE IN HEAT Table V gives the results of tests on 3 subjects with and without exercise in between the periods of gun-sight testing. "Driving" consists of simulta neously depressing the clutch pedal and pulling on the brake handle, right and left sides alternately every 7-1/2 sees. Each clutch and brake works against a weight of 40 lbs. "Lifting" involves raising 36-1/2 lbs up through 42 in. and then down It will be seen that exercise, even to the point of physical exhaustion, has little effect upon the reaction time of trained and acclimatised subjects during the ensuing hour. (See however 4(c)). 6. EFFECT OF NOISE IN HEAT In Table VI appear the results of experiments with noise on 3 subjects. This noise was produced in standard tank ear-phones worn by the subject, by means of an electronic noise generator and inter-communication set designed by N. E. Murray at the Acoustics Laboratory (National Health and Medical Research Council), University of Sydney (see AFV 49). Two levels of intensity were used - 100 and 120 db. In two experiments the noise was kept on continuously, but the experiment was terminated after 4 hours for safety. In the other two experiments, the subjects alternately removed and replaced the ear-phones every 5-10 minutes. No differentiation has yet been made in the last two experiments between the reaction times when the ear-phones were on and off. The following conclusions can be drawn from Table VI: (a) The reaction times with noise are seldom significantly greater than those of the control experiment immediately preceding the test days. (b) The reaction times with noise are invariably much greater than those of the control experiment immediately following the test days. (c) Reference to Table III indicates that this discrepancy is not likely to be due mainly to learning or acclimatisation. It is more probably attributable to the relief experienced upon cessation of noisy conditions. The subjects are, as it were, forced to train to a higher degree by the bad conditions created by noise and find. themselves better reactors when the noise is removed. (d) The differences in intensity and intermittency are without apparent effects

11 Where a fourth subject was used, the results are confirmatory. One subject appears to be more susceptible than the others, and to be more disturbed by intermittent than continuous noise. 7. EFFECT OF LACK OF SLEEP IN HEAT Table VII sets out the effects of lack of sleep upon the reaction times of 3 subjects. The following conclusions can be drawn: (a) One night without sleep increases the reaction time in heat in a significant fashion. The proportional increase is of the order of 12%. (b) One night with very short sleep following one without any does not materially alter the position. (c) A succession of further nights with very short sleep brings about an exponentially progressive failure. (d) As the reaction times increase with accumulated lack of sleep, the variability of the response also increases. Where a fourth subject was used, the results are confirmatory of (a) and (b) above. 8. EFFECT OF MEALS IN HEAT In Table VIII are set out the results obtained when meals are varied. Four subjects were used in each series. The following suggestions emerge: (a) The taking of a heavy lunch tends to increase reaction time. (b) The omission of breakfast is followed by an increased reaction time in the early part of the morning, but this effect is reduced or absent in the later part. (c) The omission of lunch as well as breakfast has no further bad effect upon the reaction time, (d) The taking of a normal lunch after the omission of breakfast does not improve the reaction time,

12 9. EFFECT OF RESPIRATORS This has been dealt with in detail in a previous report. (Fatigue Laboratory Secret Report No. 2). The essential results are repeated here in Table IX. The following conclusions can be drawn: (a) The wearing of respirators markedly increases the reaction time by 19-39o. (b) This effect is greatest under hot conditions. (c) The variability of response is increased by respirators under hot conditions. (d) Mark VI anti-dim reduces the interference in temperate atmospheres by an amount which is probably significant. (e) The light type of mask reduces the interference in the hot atmospheres by an amount which is possibly significant. (f) The wearing of respirators makes any increase of reaction time brought about by heat much more pronounced. 10. COMPARISON OF PHYSICAL WITH PSYCHO-MOTOR REACTIONS Table X sets out the relevant figures for two sets of experiments, from which the following conclusions may be drawn: (a) As the effective temperature increases from 88 to 96~F the physical reactions, as indicated by the pulse rate and rectal temperature, rise markedly, while the psycho-motor reactions remain relatively constant. (b) With progressive lack of sleep the physical reactions show a transitory rise on the second day, but return to the original levels in succeeding days, while the psycho-motor reactions show progressive deterioration. (c) Psycho-motor deterioration and physical failure are separate phenomena which can be differentiated from each other to a surprising degree under the conditions studied. In those experiments dealing with exercise also, there was no significant deterioration in psycho-motor reactions, when physical failure was imminent.

13 11. CONCLUSIONS AND PRACTICAL APPLICATIONS The problem of "fatigue" is a confused one. Straight out muscular fatigue is fairly easily understood; so is sheer mental exhaustion. Themajority of "fatigue" cases, however, fall somewhere between these two extremes and the relative mental and physical aspects are hard to differentiate. (As used here, "fatigue" may be said to be present when, without any intercurrent factor, the subject is unable to continue in his occupation without loss of efficiency,) Because of the difficulty surrounding the basic study of intermediate types of fatigue, it is difficult to formulate prediction tables for the conditions under which fatigue will occur or the extent to which it will develop. It is frequently necessary, therefore, to make special studies of those conditions which are likely to be met. In these experiments we have studied certain combinations of heat with other stresses, with a view to ascertaining those combinations which are particularly productive of fatigue, and of determining the extent to which "psycho-motor" as opposed to "physical" responses are affected. 11.1. Conclusions From the results reported here the following general conclusions may be drawn for the conditions studied. (a) In the performance of a repetitive task demanding attention, speed and precision, the learning curve pursues an exponential form. There is a rapid rate of learning in the first day or so, but this is followed by a much slower adjustment lasting several days. Under the conditions used in the experiments, an optimum speed of exact performance is obtained in 7 -14 days. (b) With such a task there is also a "boredom" factor which makes itself increasingly felt. The optimum response is succeeded by a rise in reaction time. (c) The learning and boredom curves vary both in amplitude and time with the individual and with the conditions. (d) Conditions which are uncomfortably hot are accompanied by 5-12% increase in reaction time. (e) Within this range, however, the degree of heat has no further effect upon the reaction time of subjects seated at rest.

14 (f) Subjects undertaking moderate physical exercise between tests may show some further increase in reaction time with those high degrees of heat which threaten physical continuance. (g) A hot dry atmosphere may induce a further 10% rise in reaction time over that in a hot humid atmosphere of the same effective temperature, at least in subjects acclimatised to the latter. (h) Exercise, even to the point of physical exhaustion has little effect upon the reaction time of trained and acclimatised subjects, as measured in the post-exercise period. (i) Noise does not significantly increase the reaction time of most subjects. (j) Subjects trained to operate under the bad combination of high noise levels and sub-critical heat may show improved reactions under heat alone when the noise is discontinued. (k) One night without sleep increases the reaction time by about 12%. A succession of further nights with very short sleep brings about an exponentially progressive failure. Under our conditions, four nights of twohour sleep following one night without sleep led to complete failure, (1) Meals have some effect upon reaction time. A heavy lunch tends to increase it; omission of breakfast brings about a transitory increase in the first part of the morning, but the subsequent taking or omission of lunch has little material effect. (m) The wearing of respirators increases reaction time by 20-40%, especially under hot conditions. (n) It is possible to induce physical failure with little or no psycho-motor deterioration. This is characteristically seen in severe degrees of uncomplicated heat and in exercise under hot conditions. (o) Conversely, it is possible to induce marked psycho-motor deterioration with little physical reaction. This is characteristically seen with lack of sleep. (p) In general, as reaction times increase, the variability of the reaction times increases. 11.2. Applications In many cases these results are what we may have expected, but in the field of human endeavour, it is unwise to base practice upon expectations when measurements can be made. It is true that the results reported here

15 have been obtained under artificial conditions, that the degree of heat used is extreme and that the number of subjects used is limited. Nevertheless, certain points seem to be sufficiently well established or coincide so well with general impressions as to warrant practical use. The following points are of practical importance: (a) These studies emphasize that in any repetitive task which is not purely automatic, i.e., in one which requires conscious judgement by the operative, it is important to determine the general nature of the learning and the subsequent "boredom" curves and the main factors influencing their range and duration. The time periods involved may vary from hours or days to months. It should be possible to devise simple but sufficiently adequate practical working tests to determine this in the field. (b) It is often important to remember that the rapid initial improvement is not the end of learning. (c) Good and bad reactors cannot be properly differentiated by a single test on apparatus and under conditions with which they are not very familiar. Repeated runs on successive days may be adequate, but even then the bad reactors may include slow learners who, given time, may become useful operators. Moreover, those who learn quickly may become bored quickly. (d) Conditions which are uncomfortably hot are likely to result in some loss of psycho-motor efficiency, but this is not progressive. (e) Meals taken in the course of critical work periods under hot conditions should, if possible, be light. (f) By building up training to conditions which are more severe than expected in actual operations, a more effective performance may be achieved. (g) Psycho-motor performances (such as gun-laying, instrument setting, etc.) may be maintained at a relatively high level under severe conditions, even though physical failure is imminent, where the stress is mainly physical (e.g., heat, exercise). (h) On the other hand, where nervous stresses are operating (e.g., lacking sleep), physical reactions are worthless as indices of psycho-motor ability. (i) The wearing of respirators interferes markedly with this type of performance. Improvements in mask type and anti-dim compounds have relatively small influence.

16 12. FURTHER WORK REQUIRED Certain data already obtained have yet to be examined more closely. No mention has been made in this report of the elevation and traverse approach tracings made with the improved apparatus. A further report will be made at a later date. Amongst the questions arising out of the discussion above, the following call for laboratory investigation with the present apparatus: (a) The relation of the learning curve to heat and other experimental conditions; (b) The ultimate shape of the boredom curve and the factors governing its development; (c) The effect of acclimatisation to hot wet and hot dry conditions respectively upon reactions under the two conditions; (d) The comparative effect of temperature upon the reactions produced by lack of sleep and meals; (e) The effect of dehydration upon reactions; (f) The effect of spaced repetitions upon the maintenance of learning without boredom. It is desirable that parallel investigations should be made of reactions requiring long-continued alertness such as those involved in maintaining watch. In the field, it is desirable that simple workable tests should be devised to determine the learning and boredom curves for given operational procedures requiring frequent repetition. 15. ACKNOWLEDGMENTS The authors wish to thank the 4 Armd. Bde., for their assistance throughout the experiments and the subjects for their co-operation in a routine which inevitably became wearisome at times. The tracing and prints were made by the Brisbane City Council, the photographs by A. Tuffley and reproductions by Queensland Government Printer. H. Le Breton assisted during the temporary absence of one of the authors.

17 PREVIOUS REPORTS 1. Fatigue Laboratory Secret Report No. 1 - Field Investigation in the Incidence of Tropical Fatigue (Preliminary Report). 2. Fatigue Laboratory Secret Report No. 2 - Effect of Respirators (Anti-Gas) upon gun-sighting performance. 3. List of A.FV, and P.R.C. Reports obtainable upon request by authorised persons.

TABLE I EXPERIMENTS SCHEDULE OF IN SERIES T/9 Letter Atmosphee Special Effective W Day Order for Individual Subjects Letter TAtmosphere Conditions F ork G5 I G6 | G7 I G8 Av c Temp 70 Rest 13 4 5 5 6.75 g Hot Wet — 83.5 Drivig 14 5 4 4 6.7 J Hot Wet Respirators 83.5 Rest 17 8 8 8 10.25 on/off k Hot Dry --- 84.5 Driving 15 6 6.75 1 Hot Wet Heated Walls 88.5 Driving 16 7 6 6 8.75 m HQt Wet Heated Walls 92.5 Driving 18 9 9 9 11.25 ClOsed Back cr Termp 70 Rest 20 11 11 11 1.25 gr Hot Wet — 83.5 Driving 19 10 10 10 12.25 |G9 I G10 I Gll I G12 Av. n Hot Wet Heated Walls 88.5 Driving 10 10 8 8 9.00 Normal Breakfast Heavy Lunch o Hot Wet Heated Walls 88.5 Driving 11 11 9 9 10.00 No Breakfast Normal Lunch p Hot Wet Heated Walls 88.5 Driving 12 12 10 10 11.00 No Breakfast No Lunch H

TABLE II SCHEDULE OF EXPERIMENTS IN SERIES M/1 Effective Day Order for Individual Subjects Letter Special Conditions Temp. ~F I G13 I G14 I G15 | G16 I Av. 11~ ~ ~~~~~~~~~eM,,,i,, 1,,,,,j,...., a Standard b Standard c Standard d Standard e Standard f Standard fr Standard frr Standard g Intermit. Noise 100 db h Contin. Noise 100 db i J k 1 Intermit. Noise 120 db Contin. Noise 120 db Normal breakfast, heavy lunch No breakfast, normal lunch 88 90 92 94 96 Critical* Critical Critical Critical Critical Critical Critical Critical Critical Critical Critical Critical Critical Critical Critical Critical Critical 65 4 6 8 7 5 9 14 18 10 11 12 13 16 15 17 19 20 21 22 3 4 6 8 7 5 9 14 18 11 10 13 12 16 15 17 20 8 8 6 6 6 6 4 4 6 5 5 6 7 7 6 12 12 10.5 - 15 14.3 17 20 18.25 16 18 13.75 15 19 13.75 _- 16 13.7 -- 17 14.0 13 13 14.5 14 14 14.5 11 11 14.0 10 9 14.5 9 10 14.5 18 21 20.25 19 22 21.25 20 23 22.25 21 24 23.25 22 25 24.25 3 3 3 \O m No breakfast, no lunch n Lifting 15 sec. interv. o Lifting 7-1/2 sec interv. p No sleep 1 night ql No sleep 1 night + 2 hrs 1 night q2 No sleep 1 night + 2 hrs 2 nights q3 No sleep 1 night + 2 hrs 3 nights q4 No sleep 1 night + 2 hrs 4 nights r Standard (Preliminary) 19 21 22 23 24 25 3 *Fixed (in the light of experiments a-e) at 940F.

TABLE III EFFECT OF REPETITION UPON GUN-LAYING REACTION TIMES Conditions Av.g. Atmospheric ET. n Operation Means (1/100 sec Ex. Conditions OF between Dy 2nd hr 4th hr 7th hr Day Test Hours Order T/9a T/9b T/9c T/9cr T/9g T/9gr M/lr M/ld M/lfr M/lfrr A - Original Apparatus (4 Subjects) 70 Rest 3.75. 70 Rest 4.75 - Temp. Temp. Temp. Temp. Hot Wet Hot Wet Temp. Hot Wet Hot Wet Hot Wet Hot Wet 70 Rest 6.75 458 + 4.3 438 + 70 Rest 13.25 475 + 6.1 453 + 83.5 Driving 6.75 469 + 3.9 459 + 83.5 Driving 12.25 500 + 5.7 496 + B - Improved Apparatus (3 Subjects) 65 Rest 3.0 597 + 27.5 504 + 94 Rest 6.3 429 + 13.2 457 + 94 Rest 10.0 377 + 14.6 361 + 94 Rest 14.3 331 + 12.1 338 + 94 Rest 18.7 395 + 15.7 355 + 4.2 6.5 3.6 8.0 36.2 19.1 13.0 8.6 13.8 437 + 448 + 448 + 3.3 4.4 2.9 542 455 444 459 459 496 + 10.4 + -3-1 + 4.2 + 4.3 + 2.9 + 4.1 0 o 526 + 24.3 415 + 4.3 387 + 9.1 342 + 11,8 364 + 10.2 544 + 434 + 375 + 337 + 371 + 19.9 8.4 6.5 5.0 8.3

Atmospheric. Conditions T/9c T/9j T/9cr M/2a M/2d M/2b M/2e M/2c M/2f Temp. Hot Wet Heated Tank Temp. Temp. Hot Wet Temp. Hot Wet Temp. Hot Wet TABLE IV EFFECT OF HEAT ALONE UPON GUN-LAYING REACTION TIMES E.T. Conditions Avg Operation Means (1/100 sec between Day OF 2nd hr 4th hr 7th hr Day Test Hours Order 2.hr A - 'Temperates/Hot Wet, at Rest (without Respirator) 70 Rest 6.75 458 + 4.3 438 + 4.2 437 + 3.3 444 + No respirator 83.5 Rest 10.25 471 487 465 474 + Respirator on 70 Rdst 13.25 475 + 6.1 453 + 6.5 448 + 4.4 459 + No Respirator B - Temperate/Hot Wet, at Rest (without Respirator) 65 Rest 24 + 4 379 429 390 399 + S.V. Respirator on 94 Rest 24 + 4.3 435 459 447 + S.V. Respirator on 65 Rest 24 + 5.7 395 441 394 410 + I L.V. Respirator on 94 Rest 24 + 3.3 422 428 475 442 + L.V. Respirator on 65 Rest 24 + 2.7 409 372 376 386 + L.VI. Respirator on 94 Rest 24 + 3.0 -- 418 --- L.VI. Respirator on 4.2 6.5 4.5 18.7 8.8 14.2 16.7 11.2

TABLE IV (cont.) Atmospheric E.T. ondit Avg. Operation Means (1/100 sec) Exp. Conditions between Day Conditions OFTest Hours Order 2nd hr I 4th hr 7th hr Day I.,.,I Test Hours. I Order I... C - 5 DegreeE M/la M/lb M/lc M/ld M/le Hot Hot Hot Hot Hot Wet Wet Wet Wet Wet 88 90 92 94 96 Rest Rest Rest Rest Rest 3 of Hot 6 6 6 6 6 3 of Hot 6.75 8.75 Wet, at Rest 455 + 13.8 496 + 24.9 467 + 16.6 469 + 24.7 475 + 15.7 482 + 7.8 468 + 6.9 497 + 13.6 473 + 15.2 Wet, after Driving 469 + 3.9 459 + 3.6 477 + 5.3 455 + 2.9 47J 43Y 455 47C L +D + -.0. 11.5 14.9 10.5 5.6 2.9 4.9 474 + 9.9 457 + 10.3 472 + 6.0 478 + 6.7 D - 3 DegreeE T/9g Hot Wet T/91 Hot Wet Heated Tank T/9m Hot Wet Heated Tank Closed Back T/9gr Hot Wet 83.5 88.5 Driving Driving 448 + 466 + 459 + 466 + 2.9 p 3.3 92.5 Driving 11.25 551 + 1.9 539 + 6.0 545 + 3.6 83.5 Driving 12.25 E - Hot Wet/Hot Dry, 6.75 6.75 500 + 5.7 after Driving 469 + 3.9 522 + 7.1 496 + 6.8 496 + 4.1 T/9g T/9k Hot Wet Hot Dry 83.5 84.5 Driving Driving 459 + 504 + 3.6 7.9 448 + 2.9 498 + 7.2 459 + 508 + 2.9 4.9

TABLE V EFFECT OF EXERCISE UPON GUN-LAYING REACTION TIMES IN HEAT.................Conditions Avg, EP^ Atmospheric E.T. Conditions Avg Operation Means (1/100 see) ~~Exp.^~~ Cntbetween Day Conditions F est Hurs Order 2nd hr. th hr 7th hr Day Test Hours Order T/9j Hot Wet Heated Walls 83.5 Rest S.V. Respirator on 10.25 471 465 474 + 6.3 T/91 Hot Wet Heated Walls 88.5 Driving 8.75 477 + 5.3 455 + 2.9 466 + 4.9 466 + 3-3 Control* M/ln M/lo Hot Wet Hot Wet Hot Wet 94 Rest 94 Lifting 15 sees Intervals 94 Lifting 7-1/2 sees Intervals 15.0 438 + 18.0 14.5 443 + 22.3 f) 441 + 5.5 *Exp. M/lfrr for G13 and 14, M/lf for G15 and 16.

Exp. Atmospheric I Exp. Conditions 1st Hot Wet Control* M/lg Hot Wet M/lh Hot Wet M/li Hot Wet M/ij Hot Wet 2nd Hoe Wet Control** *Exp. M/lf for G13 and 14, M **Exp. M/lfr for G13 and 14, I TABLE VI EFFECT OF NOISE UPON GUN-LAYING REACTION TIMES IN HEAT ET~ Conditions Avg eration Me OF throughout Day..nd hr..... Dayy Order 94 _:est 11.0 386 + 13.4 365 + 15.7 No Noise 94 Rest Intermitt. 13.0 422 + 12.6 353 + 3.3 Noise 100 db 94 Rest. Contin. 13.3 392 + 29.3 359 + 14.6 Noise 100 db 94 Rest Intermitt. 13.7 378 + 18.4 374 + 8.6 Noise 120 db 94 Rest Contin. 14.0 372 + 6.9 414 + 5.0 Noise 120 db 94 Rest 16.0 338 + 10.9 329 + 10.0 ans (1/100 se ) ' 7th hr 398 + 9.4 374 + 14.7 361 + 10.8 320 + 3.8 I.ay 383 + 7.5 383 + 10.5 376 + 15.5 371 + 6.7 395 + 9.2 329 + 4.8 4) -p No Noise L/fr for G15 and 16. Vlfrr for G15 and 16. m -

TABLE VII EFFECT OF LACK OF SLEEP UPON GUN-LAYING REACTION TIMES IN HEAT p Atmospheric I Conditions - ~ I., - I I~ l I, ' M/lfrr M/lp M/lq1 M/lq2 Hot Hot Hot Wet Wet Wet.T. | Conditions oF^ ~ of OF.. i ' I Sleep 94::Normal 94 1 Night without any 94 1 Night without any + 1 Night with 2 hrs 94 1 Night without any + 2 Nights with 2 hrs 94 1 Night without any + 3 Nights with 2 hrs 94 1 Night without any + 4 Nights with 2 hrs jAvg. | _ Operation Means (1/100 sec er 2n hray Order I.....2nd.hr 4th hr..... 7 hr Day 18.3 20.0 21.0 433 + 455 + 484 + 14.8 15.7 5.7 391 + 16.6 457 + 11.0 442 + 10.1 391 + 12.4 439 + 13.7 405 + 456 + 455 + 9.2 8.2 8.2 Hot Wet 22.0 484 + 5.6 484 + 22.2 M/lqs Hot Wet M/lq4 Hot Wet 23.0 524 + 43.5 24.0 614 + 30.5 535 + 8.6 525 + 20.9 484 + 9.8 r 527 + 13.5 630 + 15.4 647 + 10.9 M/2o Hot Wet 94 Normal for 4 Nights 26.7 409 372 376 386 + 11.2

TABLE VIII EFFECT OF MEALS UPON GUN-LAYING REACTION TIMES IN HEAT Avg. Atmospheric E.T. Meal Ag. Operation Means (1/100 sec itidns OF CO~F Condit hr th hr 7th hr Day A - Driving - Original Apparatus T/9n T/9o T/9p Hot Wet Heated Walls Hot Wet Heated Walls Hot Wet Heated Walls 88.5 Normal Breakfast 9.0 Heavy Lunch 88.5 No Breakfast 10.0 Normal Lunch 88.5 No Breakfast 11.0 No Lunch 410 + 6.9 400 + 5.5 422 + 12.2 410 + 5.4 432 + 7.1 457 + 9.0 428 + 8.5 411 + 10.2 428 + 8.9 437 + 11.6 433 + 8.5 433 + 5.7 ro B - Rest - Improved Apparatus Control* M/lk M/11 M/lm Hot Wet Hot Wet Hot Wet Hot Wet 94 Normal 94 Normal Breakfast Heavy Lunch 94 No Breakfast Normal Lunch 94 No Breakfast No Lunch 13.0 390 + 10.3 14.5 404 + 12.5 396 + 5.8 599 + 14.4 596 + 1.2 422 + 14.0 393 + 8.4 472 + 23.8 412 + 11.0 395 + 8.9 393 + 4.0 425 + 13.4 411 + 5.5 425 + 9.7 14.5 425 + 10.0 14.0 458 + 10.2 *Exp. M/lfr for G13 and 14, M/lf for G15 and 16.

TABLE IX EFFECT OF RESPIRATORS UPON GUN-LAYING REACTION TIMES Avg. Atmospheric E.T. Respirator Dag Oeration Means (1/100 sec Conditions Conditions Order nd hr 4th hr 7th hr - Day 4(Subjects T/9j Hot Wet Heated Walls 83.5 Standard Anti-dim V 10.25 Off( 471 On ( 554 487 587 465 474 + 6.3 567 566 + 6.5 3 Subjects M/2a Temp. 65 Standard Anti-dim V 65 Light Anti-dim V Off 379 24 + 4 On 545 24 + 3.7 Off 395 On 526 429 510 441 575 390 399 + 18.7 518 524 + 11.7 394 410 + 14.2 539 547 + 16.7 M/2b Temp. ro -— I M/2c Temp. 65 Light Anti-dim VI 24 + 2.7 Off On 409 527 372 473 376 586 + 11.2 486 495 + 12.7 3 Subjects M/2d Hot Wet 94 Standard Anti-dim V 24 + 4.3 Off On 435 595 459 649 387* 506* 447 + 8.8 622 + 26.0 M/2e Hot Wet 94 Light Anti-dim V 24 + 3.3 Off On 422 571 428 523 475 442 + 16.7 628 574 + 22.2 M/2f Hot Wet 94 Light Anti-dim VI 24 + 3.0 Off On 418 562 374*** 527*** *Omitting G14 **Omitting G16 ***Omitting G15

TABLE X COMPARISON OF PHYSICAL WITH PSYCHO-MOTOR REACTIONS Exp. Item 1st hr 2nd hr 3rd hr 4th hr 6th hr 7th hr A - Varying Temperatures (4 Subjects) M/la Reac Time P.R. R.T. 88 98.5 455 87 98.7 80 98.7 496 84 98.8 89 99.0 471 97 99.0 M/lb Reac Time P.R. R.T. 94 98.3 467 94 98.5 94 98.4 469 92 98.5 436 101 103 98.8 98.8 M/le Reac Time P.R. R.T. 87 98.5 475 94 98.7 482 95 98 99.0 99.2 106 99.3 459 115 99.6 M/ld Reac Time P.R. R.T. - 468 95 97 98.6 99.1 99 99.2 497 99 99.3 109 99.6 470 110 99.8 M/le Reac Time P.R. R.T. 102 98.9 473 116 100.5

TABLE X (cont.) Exp. Item 1st hr 2nd hr 3rd hr 4th hr 6th hr 7th hr.1;, ~~~ ~. B - Lack of Sleep (3 Subjects) M/lp Reac Time P.R. R.T. M/lq1 Reac Time P.R. R.T. 87 98.5 98 99.1 422 96 99.1 436 101 99.5 428 93 101 99.3 99.4 104 99.6 406 102 99.9 419 109 118 100.0 100.1 M/lq2 Reac Time P.R. R.T. 88 99.1 484 91 99.3 91 99.6 __.. - 484 93 100 _ — 99.5 99.5 M/lqs Reac Time P.R. R.T. 90 524 90 99.3 91 99.4 535 92 99.3 94 99.3 523 95 99.53 99.2 M/lq4 Reac Time P.R. R.T. 88 614 95 647 90 93 99.0 99.4 99.4 99.3

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