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 AERONAUTICS BULLETIN NUMBER 
 
 9 
 
UNIVERSITY OF ILLINOIS INSTITUTE OF AVIATION 
 
 Leslie A. Bryan, Ph.D., LL.B., Director Bernice Schrader, A.M., Editor 
 
 Return this book on or before the 
 Latest Date stamped below. 
 
 University of Illinois Library 
 
 RPR -21955. 
 
 IULLETII 
 
 each month by tl ! 
 
 Li6i^iui i 1912 at t he po 
 
 University ' ' . <J 
 
 offi< e at Urbana, Illinois, under the Act of August 24, 1912. Office of Publication, 3. 
 
 Administration Building, Urbana, Illinois. 
 
BY STANLEY N. ROSCOE, Ph.D. 
 
 Department of Psychology 
 University of Illinois 
 
 Flight by 
 Periscope 
 
 /. Performing an Instrument Flight Pattern; the Influence of Screen 
 Size and Image Magnification 
 
 PUBLISHED BY THE UNIVERSITY OF ILLINOIS, URBANA 1951 
 
 Itth LMKRY OF THE 
 
 I APP 3 ,j51 
 
 UNIVERSITY OF 'U.INOIS 
 
FOREWORD 
 
 This monograph is the ninth in a series of bulletins on aviation subjects 
 which are being issued from time to time by our Institute of Aviation. It re- 
 ports the significant results of a research project in human engineering con- 
 ducted by Stanley N. Roscoe under the supervision of Professor Alexander C. 
 Williams, Jr., director of the aviation psychology laboratory of the Department 
 of Psychology, University of Illinois. 
 
 Dr. Roscoe, the author, is a Research Associate in the aviation psychology 
 laboratory and has written or collaborated in the writing and research for a 
 number of other articles evaluating aircraft instrument displays. Also, he is an 
 experienced pilot having served in the Army Air Corps as an advanced pilot 
 instructor and as a transport pilot with the Troop Carrier Command. 
 
 The research was made possible by funds provided by Special Devices 
 Center, Office of Naval Research, under Contract N6ori-71, T.O. XVI, with 
 the University of Illinois. This project was one of a series that have been and 
 will be conducted under this contract. 
 
 The Institute is glad to make available the information contained in this 
 monograph. In it, as in all publications of the Institute, the author has been 
 given complete freedom to express any opinions he may wish with the under- 
 standing that he assumes sole responsibility therefor. 
 
 Leslie A. Bryan, Director 
 March. 1951 
 
13 
 
 CONTENTS 
 
 SUMMARY 4 
 
 INTRODUCTION 5 
 
 THE PROBLEM 8 
 
 APPARATUS 10 
 
 The periscope .10 
 
 The optical system of the periscope 10 
 
 The periscope screen 12 
 
 Method of adjusting screen size 12 
 
 Method of adjusting magnification 12 
 
 The cockpit hood .13 
 
 The flight instruments , 13 
 
 EXPERIMENTAL CONDITIONS 13 
 
 Selection of screen sizes 1 3 
 
 Selection of magnification values .14 
 
 Control conditions 1 C 
 
 THE EXPERIMENTAL TASK 17 
 
 The periscope as a pursuit meter .17 
 
 Selection of the task .18 
 
 EXPERIMENTAL DESIGN AND PROCEDURE 19 
 
 Balancing of intraserial effects 19 
 
 Subjects 20 
 
 Weather . . 20 
 
 Procedure 20 
 
 Method of scoring 21 
 
 Method of grading the records 23 
 
 ANALYSIS OF EXPERIMENTAL RESULTS 23 
 
 Testing for constant errors 23 
 
 Standard deviations as performance scores 24 
 
 Transformation of the performance scores 24 
 
 Testing the transformed distributions 26 
 
 Comparison of the experimental conditions 29 
 
 Levels of performance 31 
 
 Formulation of hypotheses 35 
 
 DISCUSSION OF EXPERIMENTAL RESULTS 37 
 
 Influence of screen size 37 
 
 Influence of magnification 38 
 
 Pictorial versus symbolic attitude displays 40 
 
 Limitations on the use of the periscope 40 
 
 APPENDIX 42 
 
 A Methodology for Evaluating Pursuit Performance 42 
 
 REFERENCES 46 
 
SUMMARY 
 
 The purpose of this study was to evaluate a realistic pictorial attitude dis- 
 play in standard instrument flight tasks and to determine the influence upon 
 pilot performance of two independent variables in the design of pictorial 
 displays. 
 
 Eleven pilots flew a standard instrument flight pattern with a Cessna T-50 
 airplane in nine experimental conditions using a "periscope" as a pictorial 
 attitude display and in two control conditions. The nine experimental conditions 
 sampled two variables in the design of pictorial attitude displays: the size of 
 the display (screen size) and the magnification of the image (the width of the 
 horizontal and vertical outside angles included in an image of a given size). 
 
 In the first control condition, the pilots flew with unrestricted contact visi- 
 bility, and, in the second, with no outside visibility or cockpit attitude display. 
 A new technique was used to evaluate pilot performance in standard instrument 
 flight tasks. The results of the experiment, as evaluated by this technique, were 
 as follows: 
 
 1. Pilot performance improved with increases in the size of the attitude 
 display; equal increments in screen size resulted in diminishing increments 
 in performance, within the limits tested. 
 
 2. Pilot performance improved with increases in the outside angles in- 
 cluded in a periscope image of a given size; equal increments in horizontal 
 and vertical outside visibility resulted in increasing increments in per- 
 formance, within the limits tested. 
 
 3. Pilot performance in the nine experimental conditions showed no sig- 
 nificant interaction between screen size and image magnification. 
 
 4. Pilot performance with an eight-inch square attitude display, the largest 
 tested, was not significantly different from that achieved with contact 
 visibility. 
 
 5. Pilot performance with a two-inch square attitude display, the smallest 
 tested, was significantly worse than performance with contact visibility but 
 significantly better than performance with no cockpit attitude display or 
 outside visibility. 
 
 The following hypotheses were suggested by the experimental findings: 
 
 1. Within the range of screen sizes tested, pilot performance in standard 
 instrument flight tasks bears a linear relationship to the reciprocal of the 
 horizontal, or vertical, dimension of a square periscope screen. 
 
 2. Within the range of magnifications tested, pilot performance in standard 
 instrument flight tasks bears a linear relationship to the square of the angle 
 of outside visibility included in a periscopie image of a given size. 
 
INTRODUCTION 
 
 The pilot's immediate task in flying is to control the attitude of his 
 airplane. The term "attitude" has a meaning specific to aviation. It refers 
 to the position of the longitudinal and lateral axes of the aircraft in 
 relation to the horizontal plane. Thus, an aircraft with its nose pointed 
 above the horizon is in a "climbing attitude" and an aircraft in a banked 
 position is in a "turning attitude." 
 
 The major emphasis in the training of a pilot is directed toward 
 teaching him to judge the proper attitudes for various maneuvers and 
 to manipulate the controls accordingly. This is true even though the 
 control of the attitude of the airplane is not an end in itself. The pilot's 
 ultimate task is to direct the movement of the airplane through space. 
 
 In aviation terminology, the movement of an aircraft through space 
 is defined in terms of altitude, direction, and distance. Distance is pri- 
 marily a function of time and the speed at which the airplane flies. Alti- 
 tude and direction, or heading, are the dimensions with which the pilot 
 deals directly by controlling the attitude and the power settings of his 
 airplane. Changes in attitude and power are accomplished by manipu- 
 lating the controls in the cockpit. Of the two, attitude is the more im- 
 portant and the more difficult to control. 
 
 Vision is the pilot's only dependable source of attitude information. 
 What the pilot sees depends upon what is displayed on the instrument 
 panel within the cockpit and upon the limitations that are imposed on 
 outside visibility. When flying contact, that is, by visual reference to 
 outside objects, the pilot navigates by reference to visible landmarks and 
 uses the horizon as a reference line by which to control the attitude of 
 his airplane. 
 
 However, in the early days of flying it was found that a pilot could 
 fly an airplane through clouds by reference to three basic instruments, 
 an altimeter, a directional gyro (compass), and an airspeed indicator. 
 By using these three instruments and a clock, it is possible to determine 
 the approximate position of the aircraft. By controlling the indications 
 of these instruments, the pilot can govern the position of his aircraft in 
 relation to the outside world. 
 
 While many flights were made through clouds by use of these three 
 basic position indicating instruments, the task proved to be difficult, 
 apparently because the pilot had no direct indication of the attitude of 
 his airplane. The attitude of the airplane could be inferred from the 
 changes in the indications of the altimeter, compass, and airspeed indi- 
 cator, but none of these instruments gave a direct indication of attitude. 
 
With the invention of the so-called gyroscopic attitude instruments, 
 the task of instrument flight became much more like that of contact 
 flight and, for the first time, was accompanied by a reasonable measure 
 of safety. One of the early attitude instruments was the turn-and-bank 
 indicator. It was soon followed by the gyro horizon, known also as the 
 artificial horizon or the flight indicator. 
 
 The invention of the gyro horizon provided the pilot with a direct 
 indication of the attitude of his aircraft in relation to the horizontal plane. 
 The use of this instrument made it easier for the pilot to control altitude 
 and heading because it enabled him to control the attitude of the airplane 
 directly and, therefore, the rate of change in altitude and heading. 
 Although flying exclusively by reference to cockpit instruments became 
 a routine task, instrument flight continued to be more difficult and 
 hazardous than contact flight. 
 
 Even with long experience, pilots find instrument flight more exacting 
 than contact flight because it requires continuous attention to the instru- 
 ments and frequent computations and because of the intangible emotional 
 factor that is associated with not knowing what lies ahead. Thus, while 
 pilots can and do fly airplanes entirely by reference to cockpit instrument 
 displays, there is no doubt that flying an airplane is a safer, less fatiguing, 
 and more pleasant task when a pilot can see where he is going. 
 
 With the increasing demand for all-weather flying so that commercial 
 and military flight schedules may be maintained, it becomes the problem 
 of the psychologist as well as the engineer to ascertain how the task of 
 instrument flying can be made safer, easier, and more nearly like that 
 of contact flight. One important difference between the two still appears 
 to involve the display of attitude information. 
 
 In conventional airplanes with windows of normal size, the arc of 
 the horizon visible to the pilot in contact flight is usually more than 180 
 degrees. The line representing the horizon in the gyro horizon instrument 
 is only three inches long, and at average cockpit viewing distance it sub- 
 tends a visual angle of only eight or nine degrees. Thus the size of the 
 display of attitude information in contact flight is many times greater 
 than it is in instrument flight. 
 
 A second difference arises from the fact that the gyro horizon is a 
 symbolic instrument. The index that represents the horizon is simply a 
 three-inch metal bar that maintains a position in space parallel to the 
 horizon. It does not look like the horizon, and a certain amount of imagi- 
 nation is required to identify it with the horizon. A person seeing the 
 
 6 
 
instrument for the first time might not guess what it represents. No sym- 
 bolic- attitude display can be expeeted to be as realistic as the actual 
 horizon. 
 
 Hence it would appear that both the size and the unrealistic properties 
 of the gyro horizon may be important factors contributing to the difficulty 
 of instrument flight. However, recent trends in the design of airplanes are 
 causing further restrictions upon the display of attitude information for 
 both instrument and contact flight. While cockpit instruments are being 
 made smaller so that more of them can be crowded into the panel, the 
 windshields of airplanes are also being made smaller because of the aero- 
 dynamic and structural problems they present in high-speed flight. 
 
 There is a definite possibility that in the future some of the supersonic 
 rocket or jet propelled aircraft will be built without windshields. In order 
 for the pilot to have forward visibility, windshields must be located at the 
 front of the aircraft or must protrude above the fuselage. In either loca- 
 tion they present serious engineering problems. They disrupt the smooth 
 flow of air over the surface of the aircraft and cause undesirable "drag" 
 that tends to reduce its speed. Also, at supersonic speeds, excessive heat 
 is generated by the friction of the air passing over any surface that breaks 
 the regular smooth lines of the aircraft. This excessive heat is undesirable 
 not only because of its effect upon cockpit temperature but also because 
 of the difficulty of constructing windshields that will withstand it. 
 
 In airplanes without windshields, all flying would have to be done by 
 reference to cockpit instruments. Thus the problem of developing a more 
 adequate cockpit attitude display becomes even more pressing. 
 
 Actually, two problems are involved. First, a suitable display medium 
 must be found, one that presents the attitude of the aircraft in a realistic, 
 convincing, unmistakable manner so that the pilot will never misinterpret 
 its indications. Second, the independent variables in the design of this 
 type of display must be studied so that the one display selected for use 
 may be the best of its kind that can be built. 
 
 Many people have suggested that an attitude display might be de- 
 signed that presents the pilot with a picture of the outside world, prefer- 
 ably of what lies directly in front of his airplane. The picture could be 
 presented on a scope or a screen. In clear weather such a picture might 
 be obtained by means of television or some periscopic device similar to 
 those used in tanks and submarines. In cloudy weather a color photograph 
 of the horizon, sky, and terrain could be presented on the same screen 
 from a gyro-stabilized projector. 
 
 In 1946 and 1947, Special Devices Center of the Office of Naval Re- 
 
 7 
 
search experimented, with indifferent success, using an airplane equipped 
 with television that presented the pilot with an image of what lay ahead 
 of the aircraft. 
 
 At approximately the same time, the writer (6) was having somewhat 
 better success with an airplane equipped with a projection type periscope 
 that also presented an image of what lay ahead of the aircraft. This image 
 was projected onto a ground glass screen mounted above the cockpit in- 
 strument panel. In an experiment with this equipment, it was found that 
 pilots could make safe landings using the periscope as their only source of 
 outside visibility and with no electronic landing aids. However, this par- 
 ticular periscope was a crude device that limited the angle of forward 
 visibility to only ten degrees both horizontally and vertically, and the 
 landings made with it were not as accurate as those made in contact flight. 
 
 Nevertheless, the fact that successful flights could be made at all with 
 this equipment was encouraging. It suggested that with an improved atti- 
 tude display, one that would present an image of a wider outside angle, 
 a much higher level of pilot performance could be expected. Such a 
 display was designed and constructed. 
 
 With this instrument it has been possible not only to compare pilot 
 performance using a realistic pictorial attitude display with that in con- 
 tact flight but also to study the effects of two of the independent variables 
 in the design of such displays. The first of these variables, the size of the 
 attitude display, has already been discussed; the second, the magnifica- 
 tion of the image, is important in the design of displays of this type 
 because it controls the angular extent of the outside world that is 
 included in a display of a given size. This variable becomes an experi- 
 mental problem whenever pictorial type displays are used. 
 
 THE PROBLEM 
 
 The problem in this experiment was, first, to compare the level of pilot 
 performance achieved using a realistic pictorial attitude display to the 
 level of performance achieved with contact visibility and to that achieved 
 with no attitude display; and, second, to determine the effects upon pilot 
 performance of two independent physical variables in the design of pic- 
 torial attitude displays, namely, the size of the display and the magriifica- 
 tion of the image presented by a display of a given size. 
 
 The term "magnification" will be used consistently to refer to the ratio 
 between tin- monocular visual angle subtended by the display when 
 viewed from I") inches and the horizontal outside angle included in 
 the image. 
 
 8 
 
The plan of the experiment was as follows: 
 
 1 . To select a variety of experimental conditions to sample the two 
 variables: a. the size of the display of attitude information (screen 
 size) and b. the magnification of the image (how much of the out- 
 side world is included in an image of a given size) . 
 
 2. To select an experimental flight task that would be a fair but 
 discriminating test of a pilot's ability to perform in the various 
 experimental conditions, and to select valid criteria of performance 
 on that task. 
 
 3. To select an appropriate technique for evaluating pilot per- 
 formance on the task in a quantitative manner in terms of the cri- 
 teria selected. 
 
 4. To compare pilot performance using the experimental pictorial 
 attitude display with that achieved under the two control con- 
 ditions. 
 
 5. To determine, at the hypothetical level, the functional relation- 
 ship between pilot performance on the experimental task and the 
 two independent experimental variables. 
 
 Figure 1. The interior of the pilot's 
 cockpit showing the periscope with 
 a picture of a runway placed over 
 the screen to show how the image 
 of the runway appears to the pilot 
 during an approach to a landing. 
 
Figure 2. An exterior view of the periscope installed in a Cessna T-50. 
 
 APPARATUS 
 
 The periscope 
 
 A projection type optical attitude display was designed and con- 
 structed that presented an image of what lay ahead of the aircraft. 1 The 
 image was projected onto a ground glass screen. The display was mounted 
 directly above the instrument panel of a Cessna T-50 airplane (converted 
 UC-78) as shown in Figure 1. The plexiglass windshield of the airplane 
 was replaced by an aluminum windshield through which the unit was 
 installed as shown in Figure 2. 
 
 Although this instrument is referred to as a periscope, it is quite differ- 
 ent from conventional tank and submarine periscopes. The optical system 
 includes no prisms or mirrors, and the light rays do not go around any 
 corners. The observer looks at the image that appears on a ground glass 
 S( reen rather than into an eyepiece. 
 
 The optical system of the periscope 
 
 The optical system of the periscope was composed of five lenses 
 mounted in tandem along a single axis as shown in Figure 3. The system 
 
 1 The optical system of the periscope was designed by Dr. Robert E. Hopkins 
 of the Department of < )ptics, University of Rochester, New York. The periscope 
 was < onstructed by Mr. Albert Bowman of the aviation psychology laboratory, Dc- 
 partment of Psychology, University of Illinois. 
 
 10 
 
11 
 
produced an excellent image on a ground glass screen. The use of the 
 recently developed Fresnel type lens cemented to the screen eliminated the 
 bright spot in the center that is usually present in such optical systems. 
 Thus the brightness of the image was approximately equal over the entire 
 display area. However, the image could not be brought into sharp focus 
 simultaneously over the entire area of the screen. When the central por- 
 tion of the image was in sharp focus, the peripheral portion was slightly 
 out of focus, especially at the corners. This could not be avoided with a 
 flat screen. For practical purposes the distortion was not serious; the 
 effect is similar to aerial perspective. 
 
 The periscope screen 
 
 The periscope screen, as viewed by the pilot, can be seen in Figure 1. 
 The screen is eight inches square, which, considering the premium on 
 space in the modern aircraft cockpit, is probably almost as large as would 
 ever be used. Cord crosshairs were mounted over the face of the screen 
 to serve as reference lines for the pilot. The periscope was aligned so that 
 the intersection of the crosshairs corresponded with the longitudinal axis 
 of the aircraft. Thus the horizontal crosshair coincided with the horizon 
 in straight and level flight. 
 
 Method of adjusting screen size 
 
 Screen sizes of less than eight inches were produced in the simplest 
 possible manner. Manila cardboard masks were constructed with square 
 apertures of the various desired sizes. The masks were taped to the face 
 of the periscope as they were needed. 
 
 Method of adjusting magnification 
 
 The periscope was constructed so that the relative positions of the 
 lenses could be changed by manipulating the two metal knobs attached 
 to rods that project from the housing just below the screen. In this 
 manner the magnification of the image on the screen could be adjusted 
 so that the eight-inch screen would include an outside area of from 15 
 degrees to 40 degrees both horizontally and vertically. 
 
 Aluminum strips were cut in appropriate lengths to be used as gauges 
 for setting the lens positioning rods for the various magnifications used 
 in the experiment. 
 
 I he periscope was mounted so that the surface of the screen would be 
 approximately 15 inches from the pilot's eyes. When viewed from this 
 distance, an eight-inch screen subtends a monocular visual angle of almost 
 
 12 
 
exactly 30 degrees. Thus, if a 30-degree outside angle were included in 
 the eight-inch image, the effective magnification would be one, while a 
 15-degree outside angle spread over the eight-inch screen would result in 
 a magnification of two, and so forth. 
 
 The cockpit hood 
 
 A hood was attached around the pilot's cockpit and the side wind- 
 shield painted black. This prevented the pilot from seeing out of the 
 cockpit in any direction and also served to darken the interior of the 
 cockpit so that a clear, bright periscopic image could be seen. However, 
 enough light was permitted within the cockpit to allow the pilot to use 
 the few flight instruments essential to his performance of the experimental 
 task. 
 
 The flight instruments 
 
 Only the following conventional flight instruments were included in 
 the pilot's instrument panel: an altimeter, a directional gyro, and an air- 
 speed indicator. These instruments and a clock were used by the pilot in 
 all experimental and control conditions. The gyro horizon was removed 
 from the panel, and the turn-and-bank indicator and the vertical speed 
 indicator were covered with cardboard. 
 
 EXPERIMENTAL CONDITIONS 
 
 Since the plan of the experiment required that two independent vari- 
 ables be studied simultaneously, a factorial experimental design was 
 indicated, and a limited number of values of the two independent vari- 
 ables had to be selected. The practical number of experimental conditions 
 was further limited by the expense of flying the airplane and by the num- 
 ber of trials a subject could reasonably be expected to perform in one 
 testing session. The experimental design, to be described later, required 
 that each subject be tested in each condition, and that each subject com- 
 plete all trials in a single flight. 
 
 Three screen sizes (8", 4", and 2" square) and three magnifications 
 (2.00, 1.20, and 0.86) were selected. The various combinations of these 
 values resulted in nine experimental conditions. In addition, two control 
 conditions were included, unrestricted outside visibility and no outside 
 visibility. A summary of the eleven conditions is shown in Table 1. 
 
 Selection of screen sizes 
 
 The selection of the three screen sizes was based partially upon the 
 limitations of the periscope and partially upon previous experimental 
 
 13 
 
A 
 
 B 
 
 C 
 
 15° 00' 
 
 7° 30' 
 
 3° 45' 
 
 P 
 
 Q 
 
 R 
 
 25° 00' 
 
 12° 40' 
 
 6° 20' 
 
 X 
 
 Y 
 
 Z 
 
 35° 00' 
 
 17° 55' 
 
 9° 00' 
 
 Table 1. SUMMARY OF THE EXPERIMENTAL CONDITIONS. The nine experimental condi- 
 tions are classified according to the screen size and image magnification. The angular 
 extent of visible horizon presented in each condition is indicated by the values in the 
 body of the table. The two control conditions are listed at the bottom of the table. Here- 
 after the various conditions will be referred to by the letters shown. 
 
 Screen Size 
 Image Magnification 8" A" 2" 
 
 2.00 
 1.20 
 0.86 
 
 Control Conditions: U — unrestricted visibility; H — no outside visibility. 
 
 findings. The periscope restricted the upper limit of screen size to eight 
 inches. The lower limit of two inches was selected on the basis of pre- 
 liminary flight tests. It is doubtful that screen sizes of less than two inches 
 square would be contemplated for actual use. The intermediate value of 
 four inches was selected on the basis of the findings of a previous experi- 
 ment by the writer (7) in which it was found that successive equal incre- 
 ments in the angular extent of the visible horizon result in diminishing 
 increments in the level of pilot performance. Thus, the four-inch inter- 
 mediate screen size was selected because the linear extent of visible 
 horizon that it presented was twice as great as that presented by the two- 
 inch screen and one-half as great as that presented by the eight-inch 
 screen. 
 
 Selection of magnification values 
 
 The selection of the three magnification values to be used required 
 considerable preliminary experimentation. When the periscope was first 
 assembled, the positions of the lenses were set so that the magnifica- 
 tion oi the image when viewed from 15 inches was one. Thus, objects 
 visible on the screen, when viewed from that distance, subtended the same 
 visual angle as when viewed directly. However, a number of observers 
 agreed almosl unanimously that the apparent distance to objects viewed 
 on the periscope screen was greater than the real distance to the same 
 
 14 
 
objects viewed directly. Apparently the periscope introduced a constant 
 error in depth perception. An experiment was conducted that bore out 
 this preliminary evidence, and the constant error was taken into con- 
 sideration in selecting the magnification values to be used in the flight 
 experiments. 
 
 A pilot flying contact in the type of aircraft used in these experiments 
 has practically unrestricted forward visibility. Since in the preliminary 
 experiment an image magnification of 1.29 was found to result in sub- 
 jective equality of distance judgments when the standard observation was 
 made with unrestricted binocular visibility, this value was originally 
 selected as the central magnification value to be used in the flight experi- 
 ments. With this magnification, the angular extent of the horizon pre- 
 sented on an eight-inch screen is 23 ! /3 degrees. It was decided that the two 
 extreme magnifications should present ten degrees more and ten degrees 
 less horizon respectively. However, since the greatest magnification that 
 could be obtained with the periscope was 2.00, which presented 15 degrees 
 of horizon on the eight-inch screen, a slight compromise was made, and 
 horizontal extents of 15, 25, and 35 degrees were finally selected. These 
 values correspond to magnifications of 2.00, 1.20, and 0.86, respectively. 
 The angular extents of horizontal and vertical outside visibility presented 
 in the nine experimental conditions are illustrated schematically in 
 Figure 4. 
 
 Control conditions 
 
 Two control conditions were used in an effort to evaluate performance 
 with the periscope: In the first the pilot flew with unrestricted outside 
 visibility; in the second he flew without any outside visibility, entirely by 
 reference to the three basic flight instruments and the clock. The peri- 
 scope was covered completely by a Manila cardboard mask. 
 
 While the attitude of the airplane can be inferred from the rates of 
 the changes in the indications of the directional gyro, altimeter, and air- 
 speed indicator, no direct indication of attitude is given by any of these 
 instruments. Also, as stated previously, the gyro horizon had been removed 
 from the instrument panel and the turn-and-bank and the vertical speed 
 indicators covered. 
 
 Unfortunately, in the first control condition the pilot did not have 
 completely unrestricted visibility. Since the periscope could not be re- 
 moved during the experiment, and since only one airplane of the type 
 used was available, the pilot had to fly his "unrestricted" visibility trial 
 from the co-pilot's seat on the right side of the cockpit. The aluminum 
 
 15 
 
Outside Angles 
 
 -♦:*- C 3° 45' 
 
 -ni ; V- B 7° 30' 
 
 A 15° 00' 
 
 Screen 
 
 A 8' 
 B 4' 
 C 2' 
 
 15' 
 
 30° 
 
 • Observer 
 Magnification 2.00 
 
 Outside Angles 
 
 -* •+. R 6° 20' 
 
 -4j;fr- Q12°40' 
 
 lil/V- P 25°00' 
 
 30° 
 
 • Observer 
 Magnification 1.20 
 
 Outside Angles 
 
 ->; |4- Z 9° 00' 
 
 J ;fr- Y 17° 55' 
 
 X 35° 00' 
 
 X8' 
 Y4' 
 Z 2' 
 
 ^30°- 
 
 • Observer 
 Magnification 0.86 
 
 Figure 4. Schematic diagrams of the nine experimental conditions showing the angular 
 extent of horizontal and vertical outside visibility presented in each. 
 
 windshield through which the periscope was installed caused a consider- 
 able restriction on visibility to the left. However, a pilot flying from the 
 righl seal could see ahead and to the right. 
 
 Also, since pilots are accustomed to flying from the left scat, this 
 control condition was placed at an additional disadvantage. It was 
 anti< ipated thai the performance observed in this condition would be an 
 underestimate of the level of proficiency that could be expected of the 
 ame pilots flying from the left scat and with completely unrestricted 
 . i ibility. 
 
 16 
 
THE EXPERIMENTAL TASK 
 
 It is generally agreed that the diffieulty of the task to be performed 
 is an important factor that must be considered when evaluating aircraft 
 instruments. This fact was clearly demonstrated by Williams (9) in 1947 
 and has since been confirmed in a series of experiments by the writer and 
 others (8). In all of these experiments it was observed that when the 
 flight task was too easy, differences in pilot performance were not signifi- 
 cant even though the various instrument displays used were quite dis- 
 similar. However, when the complexity or the difficulty of the flight task 
 was increased, significant differences in pilot performance did appear. 
 
 A distinction must be made between the complexity and the difficulty 
 of a task even though the two are generally associated. Some relatively 
 complex flight tasks are not particularly difficult to execute, although 
 they may be difficult for the pilot to remember. Conversely, there are 
 many uncomplicated and straightforward flight tasks that are not diffi- 
 cult to remember but are difficult to execute. The former type is better 
 for evaluating instruments that the pilot uses to make decisions as to what 
 to do, such as navigation instruments. The latter type is better for evalu- 
 ating instruments that the pilot uses to execute his decisions. These are 
 known as flight instruments. 
 
 The periscope could be used as a navigation instrument to show the 
 pilot where he is going and to enable him to make heading decisions. 
 However, its primary purpose is to serve as a flight instrument by which 
 the pilot may control the attitude of his aircraft with respect to the 
 horizon and thereby execute his decisions. 
 
 The periscope as a pursuit meter 
 
 A flight instrument is essentially a pursuit meter, and as such it must 
 meet two requirements: It must present some index of desired perform- 
 ance and some index of actual performance. The pursuit task is to align 
 the index of actual performance with the index of desired performance. 
 In most pursuit or tracking tasks the index of desired performance is 
 presented to the operator automatically. In the flight task the index of 
 desired performance is selected by the decision of the pilot. In either case, 
 the index of actual performance is presented automatically. 
 
 The periscope presents both of these indices. The index of desired 
 performance is the horizon in straight and level flight, or some selected 
 position in relation to the horizon in other cases. The index of actual 
 performance is the position of the crosshairs on the face of the periscope 
 in relation to the horizon. 
 
 17 
 
Selection of the task 
 
 Since the periscope is primarily a flight instrument, it should be tested 
 as such. For this reason, the flight task selected should be easy to 
 memorize but relatively difficult to execute. Such a task has the additional 
 advantage of simplifying the problem of scoring. 
 
 The task selected was the "Oboe" instrument flight pattern. This 
 pattern includes climbing and gliding flight and turns in both directions. 
 Specifically, the pattern is as follows: Starting from straight and level 
 flight, the pilot makes a 360-degree standard rate (three degrees per 
 second) climbing turn to the right at a vertical speed of 500 feet per 
 minute, thus completing the turn and gaining 1,000 feet in two minutes; 
 this climbing turn is followed immediately by a 360-degree gliding turn of 
 the same rates but in the opposite direction that is completed with a loss 
 of 1,000 feet of altitude in the next two minutes. The complete pattern 
 requires four minutes to perform correctly. 
 
 For a perfectly executed pattern, the aircraft will be at a particular 
 altitude and have a particular heading at any given moment during the 
 four-minute pattern. Inaccuracies in the performance of the task can 
 thus be measured directly by comparing the momentary readings of the 
 altimeter and directional gyro with these correct values. 
 
 While the flight attitude of the airplane is not measured directly by 
 this procedure, the attitude of an airplane and its power setting are the 
 only variables under the immediate control of the pilot that determine 
 the movement of the plane through the air, or, technically speaking, the 
 relative wind. In these experimental flights the power settings of the air- 
 plane were controlled in a specified manner by the experimenter, so that 
 the only flight variable under the control of the pilot was the attitude of 
 the airplane. By controlling attitude properly, the pilot could control the 
 altitude and heading of the airplane and thereby make good his desired 
 schedule. Thus it follows that any variations made by the pilot from the 
 correct flight attitudes necessary to accomplish the specified pattern would 
 result in deviations from the correct momentary altitude and heading 
 values. Such deviations could also occur as a result of variables not under 
 the control of the pilot, such as the turbulence of the air, but they should 
 0< ( u r in a random manner and should not bias the results of the experi- 
 ment. By observing the altimeter and the directional gyro, the pilot could 
 see whether or not he was on schedule and could judge what attitude 
 < hanges should be made. 
 
 The 'Oboe" instrument flight pattern had been used in a previous 
 ' |" rimenl by the writer (7) and in a series of unpublished experiments 
 
 18 
 
by the staff of the University of Illinois' aviation psychology laboratory. 
 In these experiments it proved to be a relatively difficult task to perform 
 accurately. However, pilots could easily memorize the correct altitude 
 and heading values for each 15-second interval during the four-minute 
 trial and did not become confused concerning these indices of desired 
 performance. 
 
 EXPERIMENTAL DESIGN AND PROCEDURE 
 
 Balancing of intraserial effects 
 
 The experiment was designed so that each subject performed the 
 test pattern once under each of the experimental and control conditions. 
 Because there were 1 1 conditions in all, 1 1 pilots were used so that each 
 could perform his 11 trials in a different serial sequence. This was done 
 in an effort to balance any intraserial effects of practice and fatigue. Any 
 multiple of 11 subjects could have been used, but the expense of flying 
 the aircraft prohibited the use of a larger pilot sample. The serial se- 
 quence of the various conditions in which each subject performed the 
 experimental task is shown in Table 2. 
 
 Table 2. EXPERIMENTAL DESIGN. The serial sequence of the conditions in | 
 
 which each of eleven subjects performed the experimental task is shown. 
 Each condition appears once and only once for each subject and for each 
 serial position. 
 
 
 
 
 
 Serial Position 
 
 
 
 
 
 Subject 
 
 1st 
 
 2nd 
 
 3rd 
 
 4th 
 
 5th 
 
 6th 
 
 7th 
 
 8th 
 
 9th 
 
 1 0th 1 1 
 
 < 
 
 1 
 
 U 
 
 H 
 
 A 
 
 Z 
 
 B 
 
 Y 
 
 C 
 
 X 
 
 P 
 
 R 
 
 G 
 
 2 
 
 A 
 
 U 
 
 B 
 
 H 
 
 C 
 
 Z 
 
 P 
 
 Y 
 
 Q 
 
 X 
 
 R 
 
 3 
 
 B 
 
 A 
 
 C 
 
 U 
 
 P 
 
 H 
 
 Q 
 
 Z 
 
 R 
 
 Y 
 
 X 
 
 4 
 
 C 
 
 B 
 
 P 
 
 A 
 
 Q 
 
 U 
 
 R 
 
 H 
 
 X 
 
 Z 
 
 Y 
 
 5 
 
 P 
 
 C 
 
 Q 
 
 B 
 
 R 
 
 A 
 
 X 
 
 U 
 
 Y 
 
 H 
 
 1 
 
 6 
 
 Q 
 
 P 
 
 R 
 
 C 
 
 X 
 
 B 
 
 Y 
 
 A 
 
 Z 
 
 U 
 
 f- 
 
 7 
 
 R 
 
 Q 
 
 X 
 
 P 
 
 Y 
 
 C 
 
 Z 
 
 B 
 
 H 
 
 A 
 
 l 
 
 8 
 
 X 
 
 R 
 
 Y 
 
 Q 
 
 Z 
 
 P 
 
 H 
 
 C 
 
 U 
 
 B 
 
 / 
 
 9 
 
 Y 
 
 X 
 
 Z 
 
 R 
 
 H 
 
 Q 
 
 U 
 
 P 
 
 A 
 
 C 
 
 E 
 
 10 
 
 Z 
 
 Y 
 
 H 
 
 X 
 
 U 
 
 R 
 
 A 
 
 Q 
 
 B 
 
 P 
 
 C 
 
 11 
 
 H 
 
 Z 
 
 U 
 
 Y 
 
 A 
 
 X 
 
 B 
 
 R 
 
 C 
 
 Q 
 
 F 
 
 19 
 
Subjects 
 
 The subjects were experienced instrument pilots, most of them flight 
 instructors from the Institute of Aviation and the aviation psychology 
 laboratory, University of Illinois. The subjects were given an indefinite 
 amount of practice on the task in the various experimental and control 
 conditions before performing their test trials. The purpose of the practice 
 sessions was simply to familiarize the pilots with the particular airplane, 
 the use of the periscope, the experimental procedure, and especially with 
 the test pattern on which they were to be scored. When, in the judgment 
 of the experimenter, a pilot had demonstrated that he had memorized 
 the correct altitudes and headings for each 15-second interval of the 
 four-minute pattern and was familiar with the experimental procedure, 
 practice was discontinued. Most of the pilots received between one and 
 three hours of practice. Each subject performed his 1 1 experimental 
 trials in a single session. 
 
 Weather 
 
 Test flights were made only on days when the weather was such that 
 a complete 360-degree horizon was visible. In most cases the test flights 
 had to be made above the cloud or haze level in order to satisfy this 
 requirement. 
 
 Procedure 
 
 Each pattern was started with the airplane headed north at an indi- 
 cated altitude of 5,000, 6,000, or 7,000 feet and with an indicated airspeed 
 of 1 20 m.p.h. A pattern was started as the sweep second hand of the 
 clock passed through the 12 o'clock position. 
 
 The power settings of the airplane were controlled by the experi- 
 menter from the co-pilot's seat. As the pilot started the climbing turn, 
 the experimenter advanced the throttles from the cruising position to a 
 position appropriate for the desired 500 feet per minute rate of climb. 
 I he throttles were left in this position during the first two minutes of the 
 pattern. This position varied somewhat from flight to flight depending 
 upon the altitude at which the pattern was started and the atmospheric 
 < onditions at the time. 
 
 At the end ol the first two minutes of the pattern, the experimenter 
 
 reduced the throttle settings to the position appropriate for the desired 
 
 >00 feel per minute rate of descent. The throttles were left in this position 
 
 until thr end of the four-minute pattern. This position also varied from 
 
 ighl to flight. On the average, manifold pressures of 23 in. Hg. and 14 
 
 20 
 
in. Hg. were required for the climb and glide respectively. The propellers 
 were set at 2,000 r.p.m. at all times. 
 
 Before the first trial and at the completion of each subsequent trial, 
 the periscope was set up for the next experimental condition. This was 
 done by the subject under the direction of the experimenter. It included 
 changing the magnification of the periscopic image and/or attaching the 
 appropriate Manila cardboard mask to the face of the periscope as re- 
 quired for the particular condition. The magnification of the image was 
 controlled by adjusting the lens positioning rods by use of the aluminum 
 gages described previously. The position of the mask was controlled by 
 aligning indices drawn on the face of the mask with the horizontal and 
 vertical crosshairs on the face of the screen. These indices bisected the 
 aperture in the mask both horizontally and vertically so that the center 
 of the aperture corresponded to the longitudinal axis of the airplane. 
 
 For the unrestricted visibility trial (condition U), the subject and 
 the experimenter exchanged seats. 
 
 Method of scoring 
 
 The performances of the pilots were scored by the experimenter in 
 the following manner. The altitude and heading of the aircraft at speci- 
 fied times during the pattern were recorded to the nearest ten feet and 
 five degrees. Scores were recorded at ten-second intervals, starting 15 
 seconds after the beginning and ending 15 seconds before the completion 
 of each half of the pattern. This resulted in distributions of ten scores 
 for each half of the pattern for both altitude and direction. No scores 
 could be taken during the first few seconds or during the time between 
 the climbing and gliding portions of the pattern because the experimenter 
 was occupied adjusting the power settings of the airplane. 
 
 A copy of the protocol sheet used for recording the scores is shown in 
 Figure 5. In addition to the times at which scores were taken during the 
 four-minute pattern, the protocol sheet shows the correct altitude and 
 heading for each of these intervals. It also provides space on the right 
 side of the sheet for recording the discrepancies between the observed 
 and correct values. 
 
 Since the pilot's cockpit was surrounded by a hood, the experimenter 
 could not see all of the instruments on the left side of the instrument 
 panel that were used by the subject. By holding the hood slightly away 
 from the panel, the experimenter could see the clock and the directional 
 gyro but not the altimeter. Thus the altitude readings had to be taken 
 from a second altimeter on the co-pilot's side of the panel. 
 
 21 
 
360° Standard Climbing and Gliding Turns, 500'/min. 
 
 
 Right Climb 
 
 LeftG 
 
 fide 
 
 Right Climb 
 
 Left Glide 
 
 
 Direc- Alti- 
 
 Direc- 
 
 Alti- 
 
 Direc- Alti- 
 
 Direc- Alti- 
 
 me 
 
 tion tude 
 
 Time tion 
 
 tude 
 
 tion tude 
 Errors Errors 
 
 tion tude 
 Errors Errors 
 
 :00 
 
 North X000' 
 
 2:00 North 
 
 X000' 
 
 X Y 
 
 X Y 
 
 :15 
 
 •95 
 
 45 
 
 75 
 
 125 
 
 210 
 
 :15 315 
 
 • 25 285 
 
 875 
 
 790 
 
 
 
 
 
 •35 
 
 105 
 
 290 
 
 •35 755 
 
 710 
 
 
 
 •45 
 
 135 
 
 375 
 
 •45 ??5 
 
 6?5 
 
 
 
 55 
 
 165 
 
 460 
 
 •55 195 
 
 540 
 
 
 
 •05 
 
 195 
 
 540 
 
 3 05 165 
 
 4*0 
 
 
 
 •1 5 
 
 225 
 
 625 
 
 :15 135 
 
 375 
 
 
 
 •95 
 
 255 
 
 710 
 
 :25 105 
 
 290 
 
 
 
 •35 
 
 985 
 
 790 
 
 •35 75 
 
 910 
 
 
 
 :45 
 
 ubje 
 
 315 
 
 875 
 
 •45 45 
 
 125 
 
 
 
 rt 
 
 Serial Position 
 
 
 
 
 
 
 
 Sum X Sum Y 
 
 Sum X Sum Y 
 
 
 
 Condition 
 
 
 
 
 
 
 
 
 Sum X 2 Sum Y L> 
 
 SumX 2 SumY 2 
 
 Figure 5. A copy of the protocol sheet used for scoring performance on the experimental 
 task while in flight. The protocol sheet shows the times at which the scores were taken 
 and the correct heading and altitude for each of these times. Space is provided at the 
 right for recording the error scores. 
 
 A number of possible sources of scoring error were thereby introduced. 
 Iu the first place the experimenter had to view the clock and gyro 
 obliquely through the small space between the hood and the panel. This 
 resulted in a certain amount of parallax. The experimenter had to make 
 allowances for this. Also, the altimeter from which the experimenter 
 cored and the one by which the subject flew had to be carefully syn- 
 < hronized al frequent intervals between trials in order to reduce the 
 dis< repan< ies between them to a minimum. To determine the extent of 
 th< scoring errors from all sources, motion pictures of the pilot's instru- 
 
 22 
 
merit panel were taken during a number of pre-test trials. The scores 
 that the experimenter had recorded for these trials were then compared 
 with the photographs and were judged to be acceptably accurate. It is 
 doubtful that more accurate scores could have been obtained by any other 
 practical method. It would not have been possible to photograph the 
 pilot's instrument panel during the test trials with the periscope without 
 increasing the illumination inside the cockpit hood and thereby reducing 
 the relative brightness of the periscopic image. 
 
 Method of grading the records 
 
 The altitude and direction readings that were recorded on the pro- 
 tocol sheet during flight were later compared with the corresponding 
 correct values and the discrepancies recorded as error scores in the spaces 
 provided on the right side of the protocol sheet. If an observed altitude 
 was higher than the corresponding correct altitude, the sign of the error 
 was positive; if lower, the sign of the error was negative. If an observed 
 direction value was ahead of the scheduled rate of turn, the error was 
 positive, if behind, negative. 
 
 ANALYSIS OF EXPERIMENTAL RESULTS 
 
 Testing for constant errors 
 
 The results of the experiment were evaluated in the manner described 
 in the Appendix. The first step was to determine whether there were 
 significant constant errors in the group performances in the various 
 experimental and control conditions. 
 
 This was done by determining fiducial limits for the population means 
 for the various conditions. The sample mean for each condition was based 
 upon the means of the 1 1 subjects for that condition. The subject means, 
 in turn, were based upon the 20 error scores obtained from the per- 
 formance of a single trial. The fiducial limits for the population means 
 were based upon the value of t at the .01 level for N-l or ten degrees of 
 freedom. 
 
 These tests showed the sample constant errors for the various condi- 
 tions to be of no practical significance and justified the assumption that 
 both direction and altitude errors made on the experimental task were 
 normally distributed about the standard or schedule. The deviations indi- 
 vidual pilots made from the flight schedule usually balanced so that the 
 group tendency coincided with the schedule rather than being consistently 
 fast or consistently slow. 
 
 23 
 
Standard deviations as performance scores 
 
 The second step in the statistical treatment of the results was to com- 
 pute the standard deviations of the error scores for each subject's trial in 
 each of the conditions. Because the constant errors for the climbing and 
 gliding portions of the pattern on individual trials were frequently of the 
 opposite sign, the standard deviations were based upon the average of the 
 variances for the two halves of the pattern. This was done to avoid over- 
 estimating the true variability in performance for any given trial. The 
 formula used to compute these average standard deviations for the two 
 halves of the experimental task was 
 
 V 
 
 [SXVN C - (2X,/N,) 2 ] - [ZXVN, - (ZX./N,)'] 
 
 2 
 
 where N c and N g both equal ten. 
 
 Since each of the 1 1 subjects performed one trial in each of the 1 1 
 conditions, distributions of 1 1 standard deviations were obtained for each 
 of the conditions for both altitude and direction errors. 
 
 These statistics, which describe within trial variability, were then con- 
 sidered as measures of the levels of performance accomplished on the 
 various trials, the lower variabilities representing the better performances. 
 Throughout the subsequent statistical analyses they were treated simply 
 as performance scores. The distributions of altitude performance scores 
 for the 1 1 conditions are presented in Table 3 and those for direction in 
 Table 4. 
 
 An inspection of Tables 3 and 4 shows that there are differences 
 in the central tendencies of the distributions for the various conditions, 
 both in terms of altitude and direction performance. However, the char- 
 acteristic distribution of standard deviations with ten degrees of freedom 
 is positively skewed, and, in the present case, the variances of the distri- 
 butions are highly correlated with their central tendencies. Thus the 
 central tendencies of the distributions could not be compared by the use 
 "I normal probability statistics. 
 
 Transformation of the performance scores 
 
 Tin third step in the analysis of the results was to find an appropriate 
 transformation that would render the performance scores suitable for 
 comparison by normal probability statistics. 
 
 I he distributions resulting from a number of exponential and recipro- 
 cal transformations were plotted on probability paper. Several of the 
 tran formations resulted in distributions that approached normality, 
 
 24 
 
but only one of these also resulted in apparently homogeneous varianees. 
 This was the common logarithm of the standard deviation. 
 
 For convenience in computation the transformed scores were coded 
 in the following manner: The logarithms of the standard deviations were 
 
 EXPERIMENTAL CONDITION 
 
 Subject 
 
 U 
 
 A 
 
 B 
 
 C 
 
 P 
 
 Q 
 
 R 
 
 X 
 
 Y 
 
 Z 
 
 H 
 
 1 
 
 20.73 
 
 24.73 
 
 27.00 
 
 41.18 
 
 28.02 
 
 27.45 
 
 32.40 
 
 24.28 
 
 25.77 
 
 33.45 
 
 49.12 
 
 2 
 
 24.44 
 
 30.44 
 
 22.58 
 
 29.36 
 
 39.18 
 
 36.33 
 
 37.58 
 
 23.45 
 
 23.07 
 
 23.66 
 
 55.86- 
 
 3 
 
 23.12 
 
 31.93 
 
 28.12 
 
 44.52 
 
 26.93 
 
 29.16 
 
 47.11 
 
 15.25 
 
 39.04 
 
 51.27 
 
 89.81 
 
 4 
 
 28.42 
 
 19.30 
 
 20.06 
 
 53.05 
 
 31.94 
 
 13.10 
 
 41.07 
 
 22.77 
 
 31.03 
 
 29.07 
 
 44.44 
 
 5 
 
 24.45 
 
 17.06 
 
 26.73 
 
 46.97 
 
 32.30 
 
 32.63 
 
 27.16 
 
 14.76 
 
 25.25 
 
 25.50 
 
 51.30 
 
 6 
 
 20.65 
 
 18.84 
 
 25.38 
 
 33.42 
 
 16.22 
 
 24.03 
 
 20.58 
 
 15.83 
 
 22.75 
 
 34.15 
 
 52.49 
 
 7 
 
 19.62 
 
 38.57 
 
 42.71 
 
 41.02 
 
 32.92 
 
 28.29 
 
 34.21 
 
 27.25 
 
 28.37 
 
 30.94 
 
 49.93 
 
 8 
 
 17.69 
 
 33.18 
 
 42.15 
 
 62.57 
 
 20.15 
 
 36.30 
 
 38.60 
 
 41.56 
 
 27.61 
 
 37.76 
 
 44.55 
 
 9 
 
 20.04 
 
 21.45 
 
 29.44 
 
 42.49 
 
 21.60 
 
 36.78 
 
 17.92 
 
 19.87 
 
 26.12 
 
 26.20 
 
 71.23 
 
 10 
 
 27.53 
 
 22.64 
 
 30.90 
 
 27.20 
 
 16.70 
 
 31.06 
 
 33.13 
 
 19.31 
 
 30.17 
 
 16.51 
 
 54.24 
 
 11 
 
 29.33 
 
 23.63 
 
 19.60 
 
 27.78 
 
 24.96 
 
 26.53 
 
 31.53 
 
 33.99 
 
 21.08 
 
 30.54 
 
 34.17 
 
 Table 3. THE DISTRIBUTIONS OF PERFORMANCE SCORES. Standard deviations for alti- 
 tude control by eleven subjects in the nine experimental and two control conditions. 
 
 EXPERIMENTAL CONDITION 
 
 Subject 
 
 U 
 
 A 
 
 B 
 
 C 
 
 P 
 
 Q 
 
 R 
 
 X 
 
 Y 
 
 Z 
 
 H 
 
 1 
 
 9.15 
 
 6.10 
 
 7.23 
 
 8.25 
 
 4.26 
 
 5.21 
 
 4.14 
 
 4.77 
 
 5.41 
 
 6.48 
 
 21.65 
 
 2 
 
 5.93 
 
 7.79 
 
 7.60 
 
 12.01 
 
 6.49 
 
 6.97 
 
 6.80 
 
 6.21 
 
 6.94 
 
 3.71 
 
 23.48 
 
 3 
 
 7.75 
 
 6.64 
 
 11.08 
 
 6.40 
 
 6.10 
 
 9.00 
 
 9.94 
 
 6.49 
 
 7.57 
 
 8.22 
 
 18.83 
 
 4 
 
 6.32 
 
 4.39 
 
 7.82 
 
 9.44 
 
 6.38 
 
 4.26 
 
 8.98 
 
 3.54 
 
 3.76 
 
 7.98 
 
 12.19 
 
 5 
 
 4.14 
 
 3.84 
 
 6.22 
 
 6.28 
 
 6.67 
 
 5.29 
 
 3.81 
 
 3.55 
 
 5.76 
 
 6.13 
 
 12.19 
 
 6 
 
 3.35 
 
 3.91 
 
 3.34 
 
 6.37 
 
 4.82 
 
 5.15 
 
 5.10 
 
 3.87 
 
 2.85 
 
 5.93 
 
 7.89 
 
 7 
 
 3.71 
 
 3.39 
 
 6.72 
 
 7.36 
 
 4.54 
 
 5.49 
 
 7.15 
 
 5.50 
 
 4.03 
 
 7.12 
 
 13.97" 
 
 8 
 
 5.53 
 
 5.80 
 
 6.17 
 
 16.07 
 
 9.22 
 
 8.64 
 
 10.69 
 
 7.07 
 
 5.53 
 
 10.28 
 
 16.14 
 
 9 
 
 3.54 
 
 5.72 
 
 4.56 
 
 7.86 
 
 7.28 
 
 5.83 
 
 4.87 
 
 6.01 
 
 5.57 
 
 5.27 
 
 19.30 
 
 10 
 
 4.76 
 
 6.20 
 
 5.49 
 
 3.95 
 
 5.35 
 
 7.16 
 
 6.33 
 
 4.42 
 
 5.07 
 
 5.81 
 
 8.72 
 
 11 
 
 4.49 
 
 5.53 
 
 4.90 
 
 8.62 
 
 3.84 
 
 4.14 
 
 5.70 
 
 5.06 
 
 3.91 
 
 6.64 
 
 8.31 
 
 Table 4. THE DISTRIBUTIONS OF PERFORMANCE SCORES. Standard deviations for direc- 
 tion control by eleven subjects in the nine experimental and two control conditions. 
 
 25 
 
 
first rounded off to three decimal places and then multiplied by 1,000 
 to remove the decimal point. The altitude scores were further coded by 
 subtraction of 1,000 to reduce them to a more convenient size. Hereafter 
 these transformed and coded scores will be referred to as "V-scores" 
 since they originated from measures of variability. The distributions of 
 V-scores for altitude and direction performances in each of the nine 
 experimental conditions are presented in Tables 5 and 6, respectively. 
 
 Testing the transformed distributions 
 
 The fourth step in the analysis was to test the hypotheses that the 
 transformed scores were normally distributed and that their variances 
 were equal. The latter hypothesis was tested first, since the assumption of 
 homogeneity of variance was required for the technique that was to be 
 used in testing the hypothesis of normality. 
 
 The distributions for the nine experimental conditions were tested 
 for homogeneity of variance by use of the likelihood ratio criterion as 
 described by Mood (4). The likelihood ratio criterion for testing the null 
 hypothesis 
 
 Ho *• C 2 i = C 2 2 = • • • ~ T 2 Jfc 
 
 IS 
 
 X = 
 
 ri(-) ! 
 
 W 
 
 where Si = 2 ( X H ~ x 2 
 
 Si 
 
 and 1 hua — = c 2 i. 
 
 For cadi set of data (altitude and direction V-scores) in the present 
 experiment, n 4 = nx = n 2 = ■ ■ • = n fc = 11, and k = 9. It is easily 
 demonstrated that, lor these values of n* and k, log A can be expressed in 
 the following convenient form: 
 
 log X = 5.5 (log <j\ + log <j\ + . . . + log ffh) 
 
 - 49.5 lo K 
 
 26 
 
 Tabic 5. TABULATION OF THE ALTITUDE V-SCORES. The scores and means are present 
 in a schema suitable for a three dimensional analysis of variance. The schema is cat 
 gorical by subjects (rows), image magnifications (blocks), and screen sizes (column: 
 V 1,000 log o 1,000. 
 
unification 
 
 
 . 
 
 // 
 
 Screen Size 
 4" 
 
 2 
 
 n 
 
 Sum 
 
 
 
 Subject Score 
 
 Mean 
 
 Score 
 
 Mean 
 
 Score 
 
 Mean 
 
 Mean 
 
 
 1 
 
 393 
 
 
 431 
 
 
 615 
 
 
 1,439 
 
 
 
 2 
 
 484 
 
 
 354 
 
 
 468 
 
 
 1,306 
 
 
 
 3 
 
 504 
 
 
 449 
 
 
 649 
 
 
 1 ,602 
 
 
 
 4 
 
 286 
 
 
 302 
 
 
 725 
 
 
 1,313 
 
 
 
 5 
 
 232 
 
 
 427 
 
 
 672 
 
 
 1,331 
 
 
 2.00 
 
 6 
 
 275 
 
 
 405 
 
 
 524 
 
 
 1,204 
 
 
 
 7 
 
 586 
 
 
 631 
 
 
 613 
 
 
 1,830 
 
 
 
 8 
 
 521 
 
 
 625 
 
 
 796 
 
 
 1,942 
 
 
 
 9 
 
 331 
 
 
 469 
 
 
 628 
 
 
 1,428 
 
 
 
 10 
 
 355 
 
 
 490 
 
 
 435 
 
 
 1,280 
 
 
 
 11 
 
 374 
 
 
 292 
 
 
 444 
 
 
 i,r,o 
 
 
 
 
 4,341 
 
 394.64 
 
 4,875 
 
 443.18 
 
 6,569 
 
 597.18 
 
 )5 t 7^5 
 
 478.33 
 
 
 1 
 
 448 
 
 
 439 
 
 
 511 
 
 
 1,398 
 
 
 
 2 
 
 593 
 
 
 560 
 
 
 575 
 
 
 1,728 
 
 
 
 3 
 
 430 
 
 
 465 
 
 
 673 
 
 
 1,568 
 
 
 
 4 
 
 504 
 
 
 117 
 
 
 614 
 
 
 1,235 
 
 
 
 5 
 
 509 
 
 
 514 
 
 
 434 
 
 
 1,457 
 
 
 1.20 
 
 6 
 
 210 
 
 
 381 
 
 
 314 
 
 
 905 
 
 
 
 7 
 
 518 
 
 
 452 
 
 
 534 
 
 
 1,504 
 
 
 
 8 
 
 304 
 
 
 560 
 
 
 587 
 
 
 1,451 
 
 
 
 9 
 
 335 
 
 
 566 
 
 
 253 
 
 
 1,154 
 
 
 
 10 
 
 223 
 
 
 492 
 
 
 520 
 
 
 1,235 
 
 
 
 1 1 
 
 397 
 
 
 424 
 
 
 499 
 
 
 1,320 
 
 
 
 
 4,471 
 
 406.45 
 
 4,970 
 
 451.82 
 
 5,514 
 
 501.27 
 
 14,955 
 
 453.18 
 
 
 1 
 
 385 
 
 
 411 
 
 
 524 
 
 
 1,320 
 
 
 
 2 
 
 370 
 
 
 363 
 
 
 374 
 
 
 1,107 
 
 
 
 3 
 
 183 
 
 
 592 
 
 
 710 
 
 
 1,485 
 
 
 
 4 
 
 357 
 
 
 492 
 
 
 463 
 
 
 1,312 
 
 
 
 5 
 
 169 
 
 
 402 
 
 
 407 
 
 
 978 
 
 
 0.86 
 
 6 
 
 200 
 
 
 357 
 
 
 533 
 
 
 1,090 
 
 
 
 7 
 
 435 
 
 
 453 
 
 
 491 
 
 
 1,379 
 
 
 
 8 
 
 619 
 
 
 441 
 
 
 577 
 
 
 1,637 
 
 
 
 9 
 
 298 
 
 
 417 
 
 
 418 
 
 
 1,133 
 
 
 
 10 
 
 286 
 
 
 480 
 
 
 218 
 
 
 984 
 
 
 
 1 1 
 
 531 
 
 
 324 
 
 
 485 
 
 
 1,340 
 
 
 
 
 3,833 
 
 348.45 
 
 4,732 
 
 430.18 
 
 5,200 
 
 472.73 
 
 1 3,7 65 
 
 417.12 
 
 
 1 
 
 1,226 
 
 
 1,281 
 
 
 1,650 
 
 
 4,157 
 
 461.89 
 
 
 2 
 
 1,447 
 
 
 1,277 
 
 
 1,417 
 
 
 4,141 
 
 460.11 
 
 
 3 
 
 1,117 
 
 
 1,506 
 
 
 2,032 
 
 
 4,655 
 
 517.22 
 
 Sums 
 
 4 
 
 1,147 
 
 
 911 
 
 
 1,802 
 
 
 3,860 
 
 428.89 
 
 Through 
 
 5 
 
 910 
 
 
 1,343 
 
 
 1,513 
 
 
 3,766 
 
 418.44 
 
 Blocks 
 
 6 
 
 685 
 
 
 1,143 
 
 
 1,371 
 
 
 3,199 
 
 355.44 
 
 
 7 
 
 1,539 
 
 
 1,536 
 
 
 1,638 
 
 
 4,713 
 
 523.67 
 
 
 8 
 
 1,444 
 
 
 1,626 
 
 
 1,960 
 
 
 5,030 
 
 558.89 
 
 
 9 
 
 964 
 
 
 1,452 
 
 
 1,299 
 
 
 3,715 
 
 412.78 
 
 
 10 
 
 864 
 
 
 1,462 
 
 
 1,173 
 
 
 3,499 
 
 388.78 
 
 
 1 1 
 
 1,302 
 
 
 1,040 
 
 
 1,428 
 
 
 3,770 
 
 418.89 
 
 
 
 12,645 
 
 383.18 
 
 1 4,577 
 
 441.73 
 
 17,283 
 
 523.73 44,505 
 
 449.55 
 
Unification 
 
 
 
 Screen Size 
 
 
 
 
 
 
 
 8" 
 
 4' 
 
 ' 
 
 2" 
 
 
 Sum 
 
 Mean 
 
 
 Subject 
 
 Score Mean 
 
 Score 
 
 Mean 
 
 Score 
 
 Mean 
 
 
 1 
 
 785 
 
 859 
 
 
 917 
 
 
 2,561 
 
 
 
 2 
 
 892 
 
 881 
 
 
 1,080 
 
 
 2,853 
 
 
 
 3 
 
 822 
 
 1,045 
 
 
 806 
 
 
 2,673 
 
 
 
 4 
 
 643 
 
 893 
 
 
 975 
 
 
 2,511 
 
 
 
 5 
 
 584 
 
 794 
 
 
 798 
 
 
 2,176 
 
 
 2.00 
 
 6 
 
 592 
 
 524 
 
 
 804 
 
 
 1,920 
 
 
 
 7 
 
 530 
 
 827 
 
 
 867 
 
 
 2,224 
 
 
 
 8 
 
 763 
 
 790 
 
 
 1,206 
 
 
 2,759 
 
 
 
 9 
 
 757 
 
 659 
 
 
 895 
 
 
 2,311 
 
 
 
 10 
 
 792 
 
 740 
 
 
 597 
 
 
 2,129 
 
 
 
 11 
 
 743 
 
 690 
 
 
 936 
 
 
 2,369 
 
 
 
 
 7,903 718.45 
 
 8,702 
 
 791.09 
 
 9,881 
 
 898.27 
 
 26,486 
 
 802.61 
 
 
 1 
 
 629 
 
 717 
 
 
 617 
 
 
 1,963 
 
 
 
 2 
 
 929 
 
 843 
 
 
 833 
 
 
 2,605 
 
 
 
 3 
 
 785 
 
 954 
 
 
 997 
 
 
 2,736 
 
 
 
 4 
 
 805 
 
 629 
 
 
 953 
 
 
 2,387 
 
 
 
 5 
 
 824 
 
 724 
 
 
 581 
 
 
 2,129 
 
 
 1.20 
 
 6 
 
 683 
 
 712 
 
 
 708 
 
 
 2,103 
 
 
 
 7 
 
 657 
 
 740 
 
 
 854 
 
 
 2,251 
 
 
 
 8 
 
 965 
 
 937 
 
 
 1,029 
 
 
 2,931 
 
 
 
 9 
 
 862 
 
 766 
 
 
 688 
 
 
 2,316 
 
 
 
 10 
 
 728 
 
 855 
 
 
 801 
 
 
 2,384 
 
 
 
 11 
 
 584 
 
 617 
 
 
 756 
 
 
 1,957 
 
 
 
 
 8,451 768.27 
 
 8,494 
 
 772.18 
 
 8,817 
 
 801.55 
 
 25,762 
 
 780.67 
 
 
 1 
 
 679 
 
 733 
 
 
 812 
 
 
 2,224 
 
 
 
 2 
 
 793 
 
 841 
 
 
 569 
 
 
 2,203 
 
 
 
 3 
 
 812 
 
 879 
 
 
 915 
 
 
 2,606 
 
 
 
 4 
 
 549 
 
 575 
 
 
 902 
 
 
 2,026 
 
 
 
 5 
 
 550 
 
 760 
 
 
 788 
 
 
 2,098 
 
 
 0.86 
 
 6 
 
 588 
 
 455 
 
 
 773 
 
 
 1,816 
 
 
 
 7 
 
 740 
 
 605 
 
 
 853 
 
 
 2,198 
 
 
 
 8 
 
 849 
 
 743 
 
 
 1,012 
 
 
 2,604 
 
 
 
 9 
 
 779 
 
 746 
 
 
 722 
 
 
 2,247 
 
 
 
 10 
 
 645 
 
 705 
 
 
 764 
 
 
 2,114 
 
 
 
 1 1 
 
 704 
 
 592 
 
 
 822 
 
 
 2,118 
 
 
 
 
 7,688 698.91 
 
 7,634 
 
 694.00 
 
 8,932 
 
 812.00 
 
 24,254 
 
 734.97 
 
 
 1 
 
 2,093 
 
 2,309 
 
 
 2,346 
 
 
 6,748 
 
 749.78 
 
 
 2 
 
 2,614 
 
 2,565 
 
 
 2,482 
 
 
 7,661 
 
 851.22 
 
 
 3 
 
 2,419 
 
 2,878 
 
 
 2,718 
 
 
 8,015 
 
 890.56 
 
 
 4 
 
 1,997 
 
 2,097 
 
 
 2,830 
 
 
 6,924 
 
 769.33 
 
 »ugh 
 
 5 
 
 1,958 
 
 2,278 
 
 
 2,167 
 
 
 6,403 
 
 711.44 
 
 Blo< ki 
 
 6 
 
 1,863 
 
 1,691 
 
 
 2,285 
 
 
 5,839 
 
 648.78 
 
 
 7 
 
 1,927 
 
 2,172 
 
 
 2,574 
 
 
 6,673 
 
 741.44 
 
 
 8 
 
 2,577 
 
 2,470 
 
 
 3,247 
 
 
 8,294 
 
 921, 56 
 
 
 9 
 
 2,398 
 
 2,171 
 
 
 2,305 
 
 
 6,874 
 
 763.78 
 
 
 10 
 
 2,165 
 
 2,300 
 
 
 2,162 
 
 
 6,627 
 
 736.32 
 
 
 1 1 
 
 2,031 
 
 1,899 
 
 
 2,514 
 
 6,444 
 837.27 76,502 
 
 716.0C 
 772.7i 
 
 
 
 24,042 728.55 24,830 
 
 752.42 27,630 
 
The value of —2 log A is evaluated for signifieance by reference to the 
 cumulative Chi-square distribution for k — 1 degrees of freedom. 
 
 In the present experiment the computed values of —2 log A were 
 2.111 for the variances of the nine altitude V-score distributions and 
 1.530 for the variances of the nine direction V-score distributions. The 
 respective P-values were .975 and .990, which indicate that the differ- 
 ences among the sample variances easily could have occurred by chance 
 even though the population variances were equal. In fact, one would 
 expect to observe such homogeneous sample variances very rarely. 
 
 The assumption of homogeneity of variance having been justified in 
 both cases, the distributions were next tested for normality in the follow- 
 ing manner. The deviations of the V-scores from their respective means 
 were computed for each of the nine experimental conditions. These 99 
 deviations, of the form x^- = Vij — Vj, were pooled in a single distribu- 
 tion with a mean of zero and a variance equal to the mean of the nine 
 condition variances. The variance of the pooled distribution could be 
 computed in this manner because the assumption of homogeneity of 
 variance had been found tenable. 
 
 The best fitting normal ogive was then plotted, together with the 
 cumulated per cent distribution for the 99 deviation scores. The resulting 
 graphs for the altitude and direction V-score deviations, respectively, are 
 shown in Figures 6 and 7. The discrepancies between the observed and 
 theoretically expected frequencies were in each case found not to be 
 significant. For the altitude distribution, the Chi-square value was 7.92 
 with seven degrees of freedom, which indicates a P-value of .50 to .30. 
 Thus one would expect such discrepancies to occur by chance between 
 30 and 50 times in 100, even though the parent distribution were normal. 
 Statisticians have agreed to judge this a "good" fit. For the direction 
 distribution, the Chi-square value was 3.36, also with seven degrees of 
 freedom, which gives a P-value of .90 to .80. This is considered a "super- 
 lative" fit. 
 
 Thus the assumptions of normality and homogeneity of variance were 
 found to be tenable for both the altitude and direction V-score distri- 
 butions. 
 
 Comparison of the experimental conditions 
 
 The fifth step in the analysis of the results was to submit the means 
 of the V-scores for the nine experimental conditions to comparison by the 
 three-dimensional analysis of variance technique as described by Mc- 
 Nemar (3). The analyses were categorical by subjects (rows), image 
 
 29 
 
 ible 6. TABULATION OF THE DIRECTION V-SCORES. The scores and means are pre- 
 nted in a schema suitable for a three dimensional analysis of variance. The schema is 
 itegorical by subjects (rows), image magnifications (blocks), and screen sizes (columns). 
 = 1,000 log a. 
 

 D 
 
 
 
 1 1/" 
 
 
 
 
 
 
 •y 
 
 -la H-la 
 
 / 
 
 /•| N = 99 
 J M = 0.00 
 / a =113.70 
 A x * = 7.92 
 1 df= 7 
 
 P = .50 - .30 
 
 n. 
 
 •90 
 
 
 1 
 1 
 
 1 '/*" 
 
 -80 
 
 
 1 
 
 / 
 
 -70 
 
 
 1 
 
 /• 
 
 -60 
 
 
 1 
 
 y 
 
 -50 
 
 
 -lo 
 
 r |/+lff 
 
 -40 
 
 
 1 
 
 / N = 99 
 
 -30 
 
 
 \ 
 
 M = 0.00 
 a = 122.22 
 
 -20 
 
 
 w 
 
 X 2 = 3.36 
 
 -10 
 
 / 
 
 A 
 1 
 
 1 df = 7 
 
 1 p = .90 - .80 
 
 \ 1 
 
 o 
 o 
 
 CO 
 
 o 
 o 
 
 CN 
 
 o 
 o 
 
 o o o o 
 o o o 
 
 r— CN CO 
 
 ALTITUDE V-SCORE DEVIATION 
 
 DIRECTION V-SCORE DEVIATION 
 
 Figure 6. The cumulated per cent distribution 
 for the pooled altitude V-score deviations to- 
 gether with its best fitting normal ogive. 
 
 Figure 7. The cumulated per cent distributior 
 for the pooled direction V-score deviation! 
 together with its best fitting normal ogive 
 
 magnifications (blocks), and screen sizes (columns) as shown previously 
 in Tables 5 and 6. An inspection of the column and block means in these 
 tables shows that both the altitude and direction performances of the 
 pilots improved with each increase in screen size and with each decrease 
 in the magnification of the periscopic image. Also, the row means indi- 
 cate that there were differences in the average performances of the 11 
 pilots. 
 
 The summaries of the analyses of variance for the altitude and 
 
 direction V-scores, respectively, are presented in Tables 7 and 8. Between 
 
 subject variability was found to be significant in both cases. The difler- 
 
 ences among the means for the three screen sizes were also significant, at 
 
 the .001 level, in both cases. The differences among the means for the 
 
 three image magnifications were somewhat less significant. These differ- 
 
 were significant at the .02 level for the direction V-scores, but only 
 
 1 the .10 level for the altitude V-scores, indicating that somewhat less 
 
 confidence should be placed in the latter. None of the interaction vari- 
 
 ignificanl in the case of the altitude V-scores. For the direc- 
 
 30 
 
tion V-scores, only the screen size by subject interaction approached 
 significance. This value was significant at the .10 level only and is 
 probably of little importance. 
 
 These findings indicate that both screen size and image magnification 
 influence the level of performance attained by instrument pilots flying 
 standard flight patterns with a periscope as the only source of outside 
 visibility or attitude information. The larger the screen size and the 
 greater the outside angle included in the image, the better the flying 
 performance. Apparently there is no important interaction between these 
 two independent variables. 
 
 Levels of performance 
 
 The sixth step in the analysis of the results was to compare the per- 
 formances observed in the two control conditions with those achieved 
 using the periscope. 
 
 The distributions of altitude and direction V-scores for conditions 
 U and H are shown in Table 9. The mean of the altitude V-scores for 
 
 Source of 
 
 Sum of 
 
 
 Variance 
 
 
 Confidence 
 
 Variance 
 
 Squares 
 
 df 
 
 Estimate 
 
 F-Ratio 
 
 Level 
 
 Subjects 
 
 
 
 
 
 
 (Rows) 
 
 346,746.99 
 
 10 
 
 34,674.70 
 
 3.218 
 
 .01 | 
 
 Magnification 
 
 
 
 
 
 
 (Blocks) 
 
 62,478.79 
 
 2 
 
 31,239.40 
 
 2.899 
 
 .10 
 
 Screen Size 
 
 
 
 
 
 
 (Columns) 
 
 328,950.55 
 
 2 
 
 164,475.28 
 
 15.264 
 
 .001 
 
 RxB 
 
 
 
 
 
 
 Interaction 
 
 189,980.77 
 
 20 
 
 9,499.04 
 
 0.882 
 
 n.s. 
 
 RxC 
 
 
 
 
 
 
 Interaction 
 
 315,619.01 
 
 20 
 
 15,780.95 
 
 1.465 
 
 n.s. 
 
 BxC 
 
 
 
 
 
 i 
 
 Interaction 
 
 54,306.30 
 
 4 
 
 13,576.58 
 
 1.260 
 
 n.s. 
 
 R x B x C 
 
 
 
 
 
 
 Interaction 
 
 431,016.14 
 
 40 
 
 10,775.40 
 (error term) 
 
 
 
 Total 
 
 1,729,098.55 
 
 98 
 
 
 
 
 Table 7. SUMMARY OF THE ANALYSIS OF VARIANCE FOR THE ALTITUDE V-SCORES. 
 
 31 
 
condition U was 361.27 ± 21.89. The corresponding value for direction 
 V-scores was 705.18 ± 42.76. These values can be compared with the 
 means for the various experimental conditions shown previously in Tables 
 5 and 6 and with the means for the three screen sizes as shown in 
 Figure 8. 
 
 It was anticipated that performance in condition U, "unrestricted" 
 visibility, would represent a slight underestimate of the level of perform- 
 ance the pilots could have been expected to achieve if they had been able 
 to fly these trials from the left seat and with normal contact visibility. 
 However, the results indicate that their performances in this condition 
 were not significantly better than those attained with the periscope when 
 using the largest screen size. In fact, the performances in condition X, 
 with the largest screen size and lowest magnification, were slightly better 
 than those flown with contact visibility. When contact visibility perform- 
 ances are compared with performances using the smaller screen sizes, the 
 differences do become significant, especially for the higher magnifications. 
 
 Source of 
 
 Sum of 
 
 
 Variance 
 
 
 Confidence 
 
 Variance 
 
 Squares 
 
 df 
 
 Estimate 
 
 F-Ratio 
 
 Level 
 
 Subjects 
 
 
 
 
 
 
 (Rows) 
 
 607,079.58 
 
 10 
 
 60,707.96 
 
 6.580 
 
 .001 
 
 Magnification 
 
 
 
 
 
 
 (Blocks) 
 
 78,586.51 
 
 2 
 
 39,293.26 
 
 4.259 
 
 .02 
 
 Screen Size 
 
 
 
 
 
 
 Columns ) 
 
 215,501.90 
 
 2 
 
 107,750.95 
 
 11.680 
 
 .001 
 
 k x B 
 
 
 
 
 
 
 : nteraction 
 
 176,697.93 
 
 20 
 
 8,834.90 
 
 0.958 
 
 n.s. 
 
 1 x C 
 
 
 
 
 
 
 :nteraction 
 
 325,873.54 
 
 20 
 
 16,293.68 
 
 1.766 
 
 .10 
 
 B x C 
 
 
 
 
 
 
 Interaction 
 
 69,841.00 
 
 4 
 
 17,460.25 
 
 1.893 
 
 n.s. 
 
 R x B x C 
 
 
 
 
 
 
 nteraction 
 
 369,022.23 
 
 40 
 
 9,225.56 
 (error term) 
 
 
 
 Total 
 
 1,842,602.69 
 
 98 
 
 
 
 
 raM« I UMMARY OF THE ANALYSIS OF VARIANCE FOR THE DIRECTION V-SCORES. 
 
 32 
 
Table 9. TABULATION OF V-SCORES FOR THE TWO CONTROL CONDITIONS. 
 
 Subject 
 
 Altitude V-Scores 
 
 Direction V-Scores 
 
 Control 
 
 Condition 
 
 U 
 
 1 
 
 2 
 3 
 
 4 
 5 
 6 
 7 
 8 
 9 
 10 
 11 
 
 317 
 
 961 
 
 388 
 
 773 
 
 364 
 
 889 
 
 454 
 
 801 
 
 388 
 
 617 
 
 313 
 
 525 
 
 293 
 
 569 
 
 248 
 
 743 
 
 302 
 
 549 
 
 440 
 
 678 
 
 467 
 
 652 
 
 3,974 
 
 7,757 
 
 361.27 
 
 705.18 
 
 Sum 
 Mean 
 
 Subject 
 
 Altitude V-Scores 
 
 Direction V-Scores 
 
 Control 
 
 Condition 
 
 H 
 
 1 
 
 2 
 3 
 4 
 5 
 6 
 7 
 8 
 9 
 10 
 11 
 
 691 
 
 1,336 
 
 747 
 
 1,371 
 
 953 
 
 1,275 
 
 648 
 
 1,086 
 
 710 
 
 1,086 
 
 720 
 
 897 
 
 698 
 
 1,145 
 
 649 
 
 1,208 
 
 853 
 
 1,286 
 
 734 
 
 941 
 
 534 
 
 920 
 
 7,937 
 
 12,551 
 
 721.55 
 
 1,141.00 
 
 Sum 
 Mean 
 
 These results indicate either that normal contact performance was 
 considerably underestimated in condition U or that the pilots were able 
 to perform the task extremely well when using the full eight-inch peri- 
 scope screen. Which of these possibilities is the case cannot be determined 
 from the present results. In either case, performance with the full peri- 
 
 33 
 
700-- 
 
 650-- 
 
 600-- 
 
 550" 
 
 500-- 
 
 450- ■ 
 
 400" 
 
 — Level of performance with no outside visibility — 
 
 and no cockpit attitude display 
 (Condition H: average for altitude and direction) 
 
 Level of performance with contact visibility 
 
 i i ou 
 
 - -1 100 
 
 (Condition U: average for altitude and direction) 
 
 O 
 u 
 
 z 
 
 u 
 
 Q 
 
 z 
 2+800 
 
 -750 
 
 -700 
 
 Vi Va Vb 
 
 RECIPROCAL OF SCREEN SIZE IN INCHES 
 
 Figure 8. Hypothetical relationship between pilot performance on 
 altitude and direction control and periscope screen size within the 
 range of screen sizes tested. 
 
 scope screen, especially with the largest visible outside angle, was at a 
 highly acceptable level. 
 
 The effectiveness of the periscope as a flight instrument becomes more 
 evident when the performances in the experimental conditions arc com- 
 pared with control condition H, in which the pilots had no outside 
 visibility and no attitude instruments in the cockpit. 
 
 The mean of the altitude V-scorcs for condition H was 721.55 ± 
 33.19. For the direction V-scores it was 1 141.00 ± 51.23. These per- 
 formances were not good. In fact, they were considerably worse than the 
 I" rformances in experimental condition C in which the pilots flew with 
 thi mallesl outside angle of visibility presented on the two-inch periscope 
 1 rei n. The angular extent of visible horizon was only 3° 45' in this 
 condition. Winn the airplane was in a climbing attitude, the pilot could 
 ■ Mi' horizon ;il all. only clouds, if any were present. Even so, the 
 
 34 
 
pilots' performances in this condition were significantly better at the .05 
 and .01 levels, for altitude and direction respectively, than they were with 
 no periscopic image at all in condition H. These confidence levels were 
 determined by the £-test for correlated means. 
 
 This finding illustrates the improvement in a pilot's control of the 
 airplane that results when a direct and realistic indication of attitude is 
 displayed in the cockpit, even though the information presented is 
 meager. 
 
 Formulation of hypotheses 
 
 The seventh, and final, step in the analysis of the results was to 
 formulate hypotheses concerning the functional relationships between 
 pilot performance in the experimental task and the two independent vari- 
 ables. As in the case of the selection of a transformation equation, a num- 
 ber of functions were plotted in an effort to find a linear relationship 
 between the dependent and independent variables, within the limits 
 tested. 
 
 Since only three values were obtained for each independent variable, 
 the present results could not be expected to prove any hypothesis. How- 
 ever, for each of the two independent experimental variables only one 
 of the hypothetical relationships tested was found to be tenable in view 
 of the three experimental values obtained. This, of course, does not imply 
 that other functions might not be found that would fit the observed 
 values equally well. It does imply that the values do not refute the two 
 hypotheses. 
 
 The first hypothesis deals with screen size and states that, within the 
 range of the screen sizes tested, pilot performance bears a linear relation- 
 ship to the reciprocal of the horizontal, or vertical, dimension of a 
 square periscope screen. Pilot performance is defined in terms of the 
 altitude and direction errors, expressed in V-scores, that are made while 
 performing a standard flight pattern such as that used in the experiment. 
 
 The hypothetical function is illustrated in Figure 8. The altitude and 
 direction V-score means are plotted on the same graph against the re- 
 ciprocal of the linear screen size. The ordinate scales for the altitude and 
 direction V-scores are adjusted so that the grand means correspond. The 
 means for the altitude and direction V-scores could be plotted together 
 since their between mean variances were approximately equal. Neither 
 the altitude nor the direction values plot in a perfectly linear manner, but 
 the midpoints between the two values for each of the screen sizes do fall 
 in a straight line, and the discrepancies between the altitude and direction 
 
 35 
 
Magnification 0.86 
 
 Avg angle of visibility 20.63° 
 
 Square of average angle 
 
 of visibility = 425.60 
 
 Magnification 2.00 
 
 Avg angle of 
 [visibility 8.75° 
 Square of average 
 .angle of 
 'visibility = 76.56 
 
 Magnification 1.20 
 Avg angle of visibility 14.67 
 Square of average angle 
 of visibility = 215.21 
 
 •■825 
 
 O+800 
 
 -775 
 
 <+750 
 
 -■725 
 
 100 
 
 200 
 
 300 
 
 400 
 
 SQUARE OF AVERAGE ANGLE OF OUTSIDE VISIBILITY (DEGREES) 
 
 Figure 9. Hypothetical relationship between pilot performance on altitude and direction 
 control and angular extent of horizontal and vertical outside visibility included in a 
 periscopic image within the range of image magnifications tested. 
 
 values do not appear great enough to indicate that the values represent 
 separate functions. 
 
 The second hypothesis deals with the magnification of the periscopic 
 image. It states that, within the range of magnifications tested, pilot 
 performance bears a linear relationship to the square of the angle of 
 outside visibility included in a periscopic image of a given size. Pilot 
 performance is defined as it was previously. 
 
 The hypothetical function is illustrated graphically in Figure 9. The 
 all it in le and direction V-score means are plotted on the same graph 
 againsl the square of the angle of outside visibility included in the peri- 
 54 opic image. The means represent the averages for the three screen sizes. 
 As in the preceding graph, the ordinate scales for the altitude and direc- 
 tion V-scores are adjusted so that the grand means correspond. Again the 
 between mean variances were approximately equal. In general, the means 
 plot in a linear manner, although there is a slight indication of curvi- 
 linearity in the case of the direction means. Considered together, the 
 points do not depart far enough from linearity to warrant the rejection 
 "I the hypothesis as a good approximation. 
 36 
 
DISCUSSION OF EXPERIMENTAL RESULTS 
 
 The results of this experiment have demonstrated that pilots can per- 
 form pursuit type flight tasks with a high level of profieieney using a 
 periscope as a flight instrument. When using the periscope their per- 
 formance approached the level attained in contact flight. With the 
 largest screen size and lowest image magnification, the most favorable 
 periscopic display tested, pilot performance was as good as that achieved 
 with contact visibility. With the smallest screen size and highest magnifi- 
 cation, the least favorable periscopic display tested, performance was not 
 as good as that achieved with contact visibility but was significantly better 
 than that achieved with no outside visibility or cockpit attitude display. 
 
 Thus, while the present experiment showed the periscope to be an 
 effective attitude display, it also demonstrated that the level of per- 
 formance achieved using the periscope is influenced to a significant 
 degree by the two independent physical variables studied. 
 
 Influence of screen size 
 
 The first of these was the size of the periscope. The results indicate 
 that better performance is attained with larger screens than with smaller 
 screens but that equal increments in the horizontal and vertical dimen- 
 sions of the screen result in diminishing increments in pilot performance. 
 Increasing the size of the screen does two things: First, it increases the 
 amount of information presented by showing a greater expanse of horizon, 
 sky, and terrain; second, it increases the size of the retinal image. 
 
 This second factor warrants further discussion because it provides a 
 logical explanation for the diminishing increments in performance with 
 equal increments in screen size. The larger the screen size, the wider the 
 visual angle it subtends when viewed from a given distance. The hori- 
 zontal diameter of the fovea is approximately two degrees and that of the 
 parafovea slightly less than seven degrees Thus, when the pilot fixates 
 on the intersection of the crosshairs at the center of the screen, the larger 
 the screen, the greater the proportion of it viewed peripherally. 
 
 A screen that subtends a visual angle of 30 degrees, for example, 
 would make use of a considerable portion of peripheral vision as well as 
 central vision. However, since visual acuity falls off abruptly from foveal 
 to peripheral vision, the outer portions of a large periscope screen would 
 be expected to be of relatively less effective use to the pilot than the 
 central area. Thus, while performance would be improved by increasing 
 the size of the screen, equal increments in screen size would result in 
 diminishing returns. 
 
 37 
 
If this explanation is correct, it would be expected that better per- 
 formance could be attained with a large screen if the pilot could view 
 it from a distance greater than 15 inches so that more of the screen 
 would fall in the area of central vision. Such a possibility warrants 
 investigation. 
 
 Whatever the reasons for the observed relationship, the present results 
 indicate that the size of a pictorial attitude display influences the level of 
 pilot performance in pursuit type flight tasks to a significant degree. This 
 suggests the first reason for the fact that pilots can fly better with contact 
 visibility than they can with conventional flight instruments. When flying 
 contact, a pilot can see approximately 180 degrees of horizon at one 
 time. The gyro horizon is about three inches long and subtends a visual 
 angle of only eight or nine degrees as viewed in the cockpit. Thus, in 
 addition to being a more dependable and convincing reference, the real 
 horizon is a much larger display of attitude information. A large display 
 is simply easier to see and read than a small display. 
 
 Influence of magnification 
 
 The second independent variable studied was the angular extent of 
 the outside world that is included in a periscopic image of a given size. 
 The evidence concerning the influence of this factor was somewhat less 
 conclusive than that concerning the effects of different screen sizes. How- 
 ever, the results indicate that, within the limits of the image magnifica- 
 tions sampled, the greater the outside angle included in an image of a 
 given size, the better the flying performance. Equal increments in the 
 visible outside angles resulted in increasing increments in the level of 
 performance. 
 
 In view of the diminishing returns from equal increments in screen 
 size, this might appear at first to be a contradictory finding. However, the 
 main effect of decreasing image magnification is to bring wider horizontal 
 and vertical angles into central vision. This cannot be accomplished, 
 beyond a certain point, by increasing the size of the screen. 
 
 A second effect of increasing the outside angles included in an image 
 ol a given size is the reduction of the apparent rate of any turning move- 
 menl the aircraft makes. For example, when a pilot makes a standard 
 rate turn ol three degrees per second, using a screen that includes a 30- 
 degree outside angle, any given object on the horizon will appear on the 
 < re< n five seconds before the nose of the airplane reaches that point. The 
 |"|''"' ol the object will take ten seconds to cross the screen. However, 
 il tin same screen includes only a 1 f)-degree outside angle, the object 
 
 38 
 
will appear on the edge of the screen only 2Vi seconds before it reaches 
 the center and will cross the screen in five seconds. Strictly speaking, all 
 the time values used in this example should have been increased somewhat 
 because more of the horizon is visible on a square screen when the air- 
 plane is banked than when its wings are level, but this would not affect 
 the relationships described. 
 
 It is possible that the improvement in pilot performance that was 
 associated with increases in the visible outside angle can be partially 
 attributed to these differences in the apparent rate of turn that are 
 similarly associated with different extents of visible horizon. Some of the 
 pilots reported that the rapid apparent rate of turn that resulted from the 
 highest magnification used in the experiment was unnatural and discon- 
 certing. The variability within their performances under these conditions 
 supported this observation. The relatively slow apparent rate of turn 
 associated with the lowest magnification did not have a similar detri- 
 mental effect. 
 
 A third effect of varying the image magnification was the introduction 
 of distortion in the apparent pitch of the airplane during climbs and 
 glides. For example, if the image magnification is two, whenever the 
 airplane is not in level flight the apparent displacement of its longitudinal 
 axis from the horizon is doubled. Thus, when the airplane is pitched five 
 degrees above the horizon in a climb, its apparent pitch is ten degrees 
 above the horizon. Through long experience, pilots learn to judge quite 
 accurately the proper position of the nose of the airplane in relation to 
 the horizon for the standard climbing and gliding attitudes. 
 
 Thus, these overlearned indices of desired performance might be 
 expected to result in interference with the performance of the task when 
 artificial changes are made in the apparent relationships between the 
 nose of the airplane and the horizon. Since the lowest image magnifica- 
 tion sampled (0.86) did not result in such great distortions in apparent 
 pitch as did the highest image magnification (2.00), the present results 
 provide no evidence concerning the effect of extremely minimized pitch 
 displacement indications. 
 
 Since changes in image magnification altered the visual cues presented 
 by the image in at least three important ways, it is not surprising that 
 this variable should influence pilot performance in the manner observed 
 in the experiment. However, if outside angles larger than any used in 
 the experiment were included in the periscopic image, for any given 
 screen size, the relationship would be expected to have an inflection 
 point a short distance beyond the widest angle presented. Beyond this 
 
 39 
 
inflection point, equal increments in outside visibility should result in 
 diminishing increments in performance. If extremely wide angles were 
 included in the image presented on a flat screen, such distortion would 
 be introduced that the level of pilot performance might be expected to 
 fall. These possibilities also warrant further investigation. 
 
 Pictorial versus symbolic attitude displays 
 
 This experiment was not designed to give a direct comparison be- 
 tween pictorial and symbolic attitude displays. No symbolic attitude 
 display was used in the experiment. Thus it is not possible to determine 
 the extent to which pilot performance was influenced by the fact that the 
 periscope presented a realistic pictorial view of the outside world. Per- 
 haps if a gyro horizon as large as the full periscope screen were used, 
 performance would be equally good. However, one apparent reason for 
 the difference between pilot performances with contact visibility and 
 with conventional present-day flight instruments is the fact that no 
 symbolic attitude display, such as the gyro horizon, can be as realistic 
 as a direct view of the outside world. 
 
 For example, pilots frequently experience vertigo while flying with 
 conventional instruments, and in such cases they usually conclude that 
 the gyro horizon is giving a false indication of attitude. The real horizon 
 is a more convincing visual reference, and pilots almost never come to 
 the erroneous conclusion that the horizon is tilted. Apparently a realistic 
 pictorial attitude display, such as a periscopic image of the horizon, is 
 also a convincing reference. Thus, better performance would be expected 
 with the periscope than with the gyro horizon or any other symbolic 
 attitude display, although this comparison has not been made experi- 
 mentally. However, an experiment by Johnson (2) supports this predic- 
 tion. She found that the obedience with which pilots respond to the 
 indications of a visual display depends not only upon the confidence that 
 they have in the dependability of the display but also upon its realistic 
 appearance. 
 
 Limitations on the use of the periscope 
 
 Sin< ( . in the present experiment, the periscope was used in one stand- 
 ard Bight maneuver only, many questions remain concerning its useful- 
 ness for other tasks and under different circumstances. How do weather 
 conditions affect its use? Can pilots use it to make consistently safe 
 instrument landings? Is its usefulness limited to certain less difficult tasks? 
 
 Su< 1i questions cannot be answered with confidence at this time. For 
 purposes "I the present experiment, the periscope was used only under 
 
 40 
 
favorable weather eonditions. It must be remembered, however, that 
 eontaet flights ean be made only under similar eonditions. The ehief 
 difference between periseopie and eontaet flight is in the size of the field 
 of visibility available to the pilot. "Unfavorable" weather eonditions may 
 limit performance using the periscope more than contact performance 
 simply because, with the periscope, the entire visual field may be obliter- 
 ated; while in contact flight, under identical conditions, the pilot is able 
 to shift his focus of attention to additional areas in his field of visibility 
 that will provide the necessary cues. 
 
 For example, when the horizon is indistinct, a pilot using the periscope 
 will be at a serious disadvantage, whereas a pilot flying contact is able 
 to glance around at other portions of the horizon that may be more 
 sharply defined or at ground references below. While flying contact under 
 such weather conditions, the pilot makes considerable use of his flight 
 instruments in the cockpit to supplement outside visual cues. If the peri- 
 scope were used in operational flight, the pilot would also use the con- 
 ventional flight instruments for this purpose. The periscope will never 
 be an all-weather flight instrument since it will not penetrate clouds, but 
 certain recent television developments do have such possibilities. Also, 
 it is possible that an artificial pictorial presentation could be used as an 
 alternate method of displaying attitude information in the cockpit. 
 
 To date no controlled experiments involving take-offs and landings 
 have been conducted using this particular periscope. However, informal 
 practice using the periscope on these tasks indicates that, after a few 
 trials, pilots can perform either maneuver with reasonable accuracy and 
 safety. The binocular visual cues that a pilot normally makes use of 
 while landing an airplane are no longer present when flying with the 
 periscope. However, a pilot can soon learn to make greater use than he 
 normally does of the various monocular cues that are still available with 
 "the "periscope. Of these, perspective is probably the most important. 
 Textural changes in the image that occur as the airplane approaches the 
 ground also appear to be useful cues. 
 
 The limitations placed upon the performance of other maneuvers by 
 the use of a periscope instead of a windshield are not known at this time. 
 For tasks requiring visibility to the side or behind, the periscope obviously 
 offers no assistance. However, such tasks usually can be performed by 
 the use of radar or even side windows, which do not present the same 
 engineering problems that front windshields or canopies do. 
 
 At the present time the periscope is just a useful tool for studying the 
 principles that should be followed in designing pictorial aircraft attitude 
 
 41 
 
displays. However, the level of performance attained by the instrument 
 pilots who used the periscope in this experiment indicates that pictorial 
 attitude displays that present either a real or an artificial view of what 
 lies ahead of the aircraft may have extensive operational applications for 
 aviation in the future. 
 
 APPENDIX 
 
 A Methodology for Evaluating Pursuit Performance 
 
 In any pursuit task, the operator attempts to manipulate the equip- 
 ment in the manner necessary to make good some sort of schedule. The 
 index of actual performance is supposed to indicate some specified posi- 
 tion at any given time. In most cases this schedule is presented to the 
 operator while he is performing the task by changes in the indications 
 of the index of desired performance. In other cases the schedule is known 
 by the operator in advance. In any case the types of manipulations 
 required and the types of errors made will be essentially the same, though 
 of different magnitudes, for any particular type of pursuit task. 
 
 Any manipulation errors the operator makes will result in discrepan- 
 cies between the indications of the index of actual performance and the 
 schedule the operator is attempting to make good. These discrepancies are 
 the raw error data that are used for evaluating pursuit performance. 
 
 The schedule is used as a standard, and displacements from the stand- 
 ard are recorded as error scores of positive or negative sign. In most 
 pursuit tasks the operator has equal opportunity to make errors of either 
 sign. In this event the error scores may be expected to distribute them- 
 selves normally about the standard with a mean of approximately zero, 
 in which case, of course, they will also be normally distributed about 
 their mean. 
 
 For some types of tasks, however, the operator does not have equal 
 opportunity to make errors of either sign, and the error scores will tend 
 to be consistently positive or negative. This will result in a constant 
 error. In such cases the mean of the distribution may be significantly 
 different from the standard, and the shape of the distribution may be 
 expected to be skewed away from the standard. There is both logical and 
 empirical evidence for this statement. The logic is based upon the nature 
 ol the experimental situations in which such events occur. 
 
 Suppose, lor example, that an experimental flight task requires that 
 the pilot make good a scheduled rate of climb that is greater than the 
 airplane will perform. In this event the mean of the pilot's error scores 
 will tend to approach the standard as nearly as the power of the airplane 
 
 42 
 
will allow, but there will be greater opportunity for negative altitude 
 errors than for positive. Thus the range of altitude errors will be greater 
 in the negative direction, and the shape of the distribution of errors will 
 be skewed away from the standard. Fortunately the experimenter usually 
 can select tasks that are not subject to such limitations. 
 
 There is a second type of experimental situation in which constant 
 errors will be observed occasionally which, though statistically significant, 
 are of little practical consequence. Constant errors of this type may appear 
 even though the subject has equal opportunity to make manipulation 
 errors of either sign. For example, such constant errors may occur as a 
 result of a systematic error in recording the scores, an improper adjust- 
 ment of the experimental equipment, or other extraneous factors. In such 
 cases the error scores still should be normally distributed about their 
 own means, and appropriate corrections can be made. 
 
 Thus the first step in the evaluation of such data is to determine 
 whether the means of the distributions differ significantly from the 
 standard, that is, whether they differ significantly from zero. This may 
 be done by determining the limits, for some specified level of confidence, 
 between which hypotheses may be accepted concerning the location of the 
 population mean. If the standard lies within these limits there is no 
 reason for rejecting the hypothesis that there is no difference between the 
 population mean and the standard. 
 
 Assuming that the null hypotheses concerning the locations of the 
 population means for a number of experimental conditions have been 
 found to be tenable, the sample means for the various conditions warrant 
 no further consideration in experiments of this sort. 1 
 
 In most cases it is not the measure of central tendency that is of 
 primary interest in the quantitative description of performance in a pur- 
 suit task. The errors that are made are variable in magnitude, and it is 
 the magnitude of these deviations from the standard, or the mean, that 
 best measures the level of performance. 
 
 In modern statistical practice, the standard deviation has become the 
 conventional description of variability. This statistic describes perform- 
 ance in pursuit type flight tasks especially well because it gives appropri- 
 ate weighting to extreme deviations from the mean. Such weighting is 
 
 1 When null hypotheses concerning the population means for a number of con- 
 ditions are tested simultaneously, the computed fiducial limits based upon the 
 various sample means will occasionally fail to include the standard by chance, 
 even though the true population mean in question is not different from the stand- 
 ard. The frequency with which this will occur depends of course upon the level 
 of confidence for which the fiducial limits of the population means are computed. 
 
 43 
 
appropriate in evaluating flying performance because it is the occasional 
 extreme deviation from the desired position, rather than the frequent 
 minor deviations, that results in serious consequences. 
 
 Another less common measure of variability is the root-mean-square 
 error, as described by Chapanis, Garner, and Morgan ( / ) . This statistic 
 describes the variability about the standard rather than about the mean, 
 which is desirable in certain cases. However, it makes no distinction 
 between constant and variable errors. Thus, in the case of pursuit per- 
 formance data in which there are small but significant constant errors 
 that can be attributed to systematic extraneous factors, the standard 
 deviation is the appropriate statistic. 
 
 Just as the standard deviation of the distribution of error scores for 
 a given subject in a given condition describes the subject's performance 
 in that condition, a distribution of such standard deviations for a group 
 of subjects describes the performances of the group in that condition. 
 Used in this way, the standard deviations are to be considered as scores 
 rather than statistics. 
 
 Of course these scores, which were formerly called standard devia- 
 tions, will not be distributed normally. However, the manner in which 
 standard deviations distribute themselves is known. The shape of their 
 sampling distribution depends upon their number of degrees of freedom. 
 Thus it is possible to transform standard deviations into scores that dis- 
 tribute themselves normally. Mueller (5) discusses a number of trans- 
 formations that are appropriate to other types of scores characteristically 
 distributed in a nonnormal manner. The methods he describes are equally 
 appropriate to the transformation of any type of distribution for which 
 a satisfactory transformation equation can be found. 
 
 Since the purpose of such transformations is to render the original 
 distributions of scores for the various experimental conditions susceptible 
 to comparison by normal probability statistics, the distributions of the 
 transformed scons must justify the assumptions of normality and homo- 
 geneity <>i variance. Before the distributions of transformed scores are 
 used for comparative purposes, they should be tested to determine whether 
 or not they satisfy these requirements. If they do not, a better transforma- 
 tion must be found. 
 
 Assuming the transformation has been found to be acceptable, the 
 distributions of transformed scores may be compared by the use of sta- 
 tistics that require the assumptions of normality and homogeneity of 
 variance. Such common techniques as the analysis of variance and the 
 /-test for correlated means will usually be adequate. 
 
 44 
 
The level of significance that is found for any comparison between 
 eonditions using the transformed seores is applicable to the differences 
 between the original distributions of scores for those conditions. The 
 logical justification for this statement is this: The probabilities that were 
 determined are applicable only to the transformed distributions. However, 
 the following crucial inference may be made: Since the transformed 
 scores bear a definite, though nonlinear, relationship to the original 
 scores, if the difference between the means of the distributions of the 
 former is found to be significant, it may be inferred that the difference 
 between the central tendencies of the corresponding distributions of the 
 latter is equally significant. 
 
 45 
 
REFERENCES 
 
 1. Chapanis, A., Garner, W. R., and Morgan, C. T. Applied experi- 
 
 mental psychology: human factors in engineering design. New York: 
 John Wiley & Sons, 1949, 55-57. 
 
 2. Johnson, B. E., and Williams, A. C, Jr. Obedience to rotation-indi- 
 
 cating visual displays as a function of confidence in the displays. 
 Port Washington, New York: U. S. Navy, Special Devices Center, 
 Technical Report SDC 71-16-2, June, 1949. 
 
 3. McNemar, Q. Psychological statistics. New York : John Wiley & Sons, 
 
 1949, 289-316. 
 
 4. Mood, A. M. Theory of statistics. New York: McGraw-Hill, 1950, 
 
 269-270. 
 
 5. Mueller, C. G. Numerical transformations in the analysis of experi- 
 
 mental data. Psychol. Bull., 1949, 46, 198-223. 
 
 6. Roscoe, S. N. The effects of eliminating binocular and peripheral 
 
 monocular visual cues upon airplane pilot performance in landing. 
 /. appl. Psychol., 1948, 32, 649-662. 
 
 7. Roscoe, S. N., and Williams, A. C., Jr. Pilot performance in instru- 
 
 ment flight as a function of the extent and distribution of visible 
 horizon. Port Washington, New York: U. S. Navy, Special Devices 
 Center, Technical Report SDC 71-16-3, June, 1949. 
 
 8. Roscoe, S. N., Smith, J. F., Johnson, B. E., Dittman, P. E., and Wil- 
 
 liams, A. C, Jr. Comparative evaluation of pictorial and symbolic 
 VOR navigation displays in the 1-CA-l Link trainer. Washington, 
 D. C: C.A.A., Division of Research, Report No. 92, October, 1950. 
 
 9. Williams, A. C, Jr. Evaluation and development of aircraft instru- 
 
 ment designs. Port Washington, New York: U. S. Navy, Special 
 Devices Center, University of Illinois' Progress Report No. 5, Sep- 
 tember. 1947, 24-26. 
 
 A 6 
 
THE INSTITUTE OF AVIATION, established in 1945 as the Institute of 
 Aeronautics, is operated as the administrative agency responsible for the 
 fostering and correlation of the educational and research activities related 
 to aviation in all parts of the University. Other functions include aca- 
 demic instruction, flight training, management of the University of 
 Illinois Airport, and aeronautical research. 
 
 In connection with the latter function, the Institute issues two types 
 of publications . . . first, a group of reports on research results, and 
 second, a series of bulletins on aviation subjects of an extension service 
 nature to the citizens of the State. 
 
 The following publications have been issued: 
 Bulletin One: Municipal Airport Management, Leslie A. Bryan, 1947. 
 
 (Out of print) 
 Bulletin Two: Landscape Planting for Airports, Florence B. Robinson, 
 
 1948. 
 Bulletin Three : Labor Relations in the Air Transport Industry Under 
 
 the Amended Railway Labor Act, E. B. McNatt, 1948. 
 Bulletin Four: Airport Zoning, J. Nelson Young, 1948. (Out of print) 
 Bulletin Five : Evaluation of the School Link as an Aid in Primary 
 
 Flight Instruction, A. C. Williams, Jr., and Ralph E. 
 
 Flexman, 1949. 
 Bulletin Six : Lightplane Tires on Turf and Concrete, Leslie A. Bryan, 
 
 1949. 
 Bulletin Seven: Light Aircraft Operating Costs, Leslie A. Bryan, 1949. 
 Bulletin Eight: Evaluation of the School Link and Special Methods of 
 
 Instruction in a Ten-Hour Private Pilot Flight-Training 
 
 Program, Ralph E. Flexman, William G. Matheny, and 
 
 Edward L. Brown, 1950. 
 Bulletin Nine : Flight by Periscope : I. Performing an Instrument Flight 
 
 Pattern; the Influence of Screen Size and Image Magni- 
 fication, Stanley N. Roscoe, 1951. 
 
 Publications of the Institute of Aviation will be sent free of charge 
 upon request. 
 
1 
 
UNIVERSITY OF ILLINOIS-URBANA 
 
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