Engineering Psychology

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Engineering Psychology

Historical development


Subject matter

Man-machine system design


Engineering psychology is a branch of applied psychology specifically concerned with the discovery and application of information about human behavior and its relation to machines, tools, and jobs so that their design may best match the abilities and limitations of their human users. The field is also referred to, from time to time, as psychotechnology or applied experimental psychology, but these two names appear to be gradually dropping out of use.

Engineering psychology can be properly viewed as part of industrial psychology. The latter includes such additional topics as personnel procurement, selection, training, classification, and promotion; labor relations; morale and human relations; organizational management; and consumer behavior. The field of engineering psychology can also be identified as a subarea of human factors engineering, or human engineering, as it is generally known in the United States, or of ergonomics, as it is usually called in the United Kingdom and Europe. The broader field of human factors engineering includes, in addition to engineering psychology, portions of such human sciences as anatomy, anthropometry, applied physiology, environmental medicine, and toxicology.

These distinctions between engineering psychology, industrial psychology, and human factors engineering are more academic than real. In his practical work, the engineering psychologist needs to know enough about all of these disciplines so that he can make use of them in arriving at sensible and informed design decisions. Rather than calling engineering psychology a distinct entity, it would be more correct to say that this name is more a convenient focus around which training is offered in many universities.

Historical development

In a certain sense it is correct to say that people have been concerned with engineering psychology of a sort ever since man began fashioning implements for his own use. Nonetheless, engineering psychology has emerged as a separate discipline only within the past few decades. It was not until the end of the nineteenth century that the first systematic investigations were conducted on man’s capacity to work as it is influenced by his job and his tools. Frederick W. Taylor (1898) made empirical studies of the best design of shovels and of the optimum weight of material per shovelful for handling different products, such as sand, slag, rice coal, and iron ore. Taylor’s interests, however, were primarily in rates of doing work and in the effects of incentives and worker motivation on rates of working. It remained for Frank B. Gilbreth to set a firm foundation for this field with his classic study of bricklaying (1909). Among other things, Gilbreth invented a scaffolding which could be quickly adjusted so that the bricklayer could work at the most convenient level at all times. A shelf held the bricks and mortar at their most convenient positions. By further changes of a similar nature Gilbreth was able to increase the number of bricks laid from 120 to 350 per man per hour. This pioneering work of Taylor and Gilbreth was the beginning of that branch of industrial engineering now known as time and motion study.

In the years that followed, time and motion engineers developed a number of principles of motion economy, of the arrangement of work, and of work design that have been widely applied throughout modern industry. Insofar as they have focused on human capacities and limitations and have used this information to redesign the machine, the task, or the work environment, it is correct to say that time and motion engineers are predecessors of the modern engineering psychologist.

Still, the primary emphasis in time and motion engineering has been on man as a worker, that is, as a source of mechanical power. During the two world wars there appeared a new class of machines —machines that made demands upon the operator not in terms of his muscular power but rather in terms of his sensory, perceptual, judgmental, and decision-making abilities. The job of a sonar operator, for example, requires virtually no muscular effort, but it makes severe demands on his sensory capacity, his attentiveness, and his decision-making ability. Problems of this type could no longer be dealt with by common sense or by the time and motion engineer’s principles of motion economy.

World War I . When the United States entered World War I in 1917, a group of psychologists under Robert M. Yerkes was organized as the Psychology Committee of the National Research Council. In volunteering their services to the military establishment, they were met at first with considerable skepticism about what they could do of any value in the hard business of war. Gradually these psychologists were able to make some substantial contributions and eventually win the enthusiastic endorsement of the military services.

By and large the psychologists in World War I were concerned with such things as the selection, classification, and training of recruits, and with morale, military discipline, recreation, and problems of emotional stability in soldiers and sailors. A few of them, however, notably Raymond Dodge, Knight Dunlap, and Carl E. Seashore, encountered problems of a different sort—those in which the design of machines and equipment had to be related to the user. These early problems were found in gas masks, in binoculars and monoculars for spotters, in listening devices for locating submarines, and in aircraft. Questions were more numerous than answers, and the war ended before many solid accomplishments had been made.

World War II . After the armistice in 1918 this pioneering work in engineering psychology was almost entirely abandoned. A few scattered studies appeared between the two world wars under the auspices of the Industrial Health Board and the Industrial Fatigue Research Board of the Medical Research Council (Great Britain), but the field was largely neglected until World War n. At that time the machines and problems foreshadowed by World War I reappeared in profusion. Radar, sonar, high altitude and high speed aircraft, naval combat information centers, and air traffic control centers placed demands upon their human operators that were often far beyond the capabilities of human senses, brains, and muscles. Operators sometimes had to look for targets which were all but invisible, understand speech against backgrounds of deafening noise, track targets simultaneously in the three dimensions of space with both hands, and absorb large amounts of information to reach life-and-death decisions within seconds. As a result, bombs and bullets often missed their mark, planes crashed, friendly ships were sunk, and whales were depth-charged. The response to the need was so vigorous and dramatic that only a few highlights can be mentioned here.

Having entered the war before the United States, Great Britain faced these problems first and established a pattern that, in broad outlines, was followed later in the United States. The Medical Research Council was responsible for sponsoring much research on man—machine problems in several large universities and in the military services through the Flying Personnel Research Committee, the Royal Naval Personnel Research Committee, and the Military Personnel Research Committee. In the military services, important work was done at such laboratories as the Royal Aircraft Establishment, Farnborough; the Admiralty Naval Motion Study Unit, London; and the Admiralty Research Laboratory, Teddington, Middlesex.

Although entering the conflict later, the United States met problems equally urgent and dealt with them in substantially the same way. The National Defense Research Committee through the Office of Scientific Research and Development set up numerous research contracts in universities and industries to study these problems. All three military services incorporated civilian and military scientist-psychologists into their research and development laboratories in order that research findings would be put to immediate use. Some of the pioneering work in this area was carried out by the Aero Medical Laboratory of the (then) Army Air Forces Air Materiel Command, Wright Field, Dayton, Ohio; the Army Air Forces School of Aviation Medicine, Randolph Field, Texas; the U.S. Navy Electronics Laboratory, San Diego, California; the Naval Research Laboratory, Washington, D.C.; and the Armored Medical Research Laboratory, Fort Knox, Kentucky.

Present status of the field . Since World War II the growth of engineering psychology has been very rapid. The Society of Engineering Psychologists, Division 21 of the American Psychological Association, had 360 members in 1965. About 770 psychologists are members of the Human Factors Society and, indeed, make up over 60 per cent of the membership of that organization. Psychologists also figure prominently in the Ergonomics Research Society (centered in Great Britain), the Societe d’Ergonomie de Langue Française (centered in France), the Nederlandse Vereniging voor Ergono-mie, and the Japanese Ergonomics Research Society. Engineering psychologists are employed in every branch of the military service, in many independent research and consulting organizations, and in the aviation, automotive, electronics, communications, and home appliance industries.

At the present time, engineering psychology is most fully developed and exploited as a specialty in the United States. Other countries which give training in this area or make use of it in practical affairs to some degree or other are Australia, Belgium, France, Germany, Great Britain, Israel, Japan, the Netherlands, Sweden, Switzerland, and the U.S.S.R.


Engineering psychologists aim to discover principles that can be cast into the form of recommendations for machine design. Unfortunately, they can usually find specific answers for only a small proportion of the questions they face. Part of the difficulty is that man-machine interactions occur in an almost infinite variety. Moreover, the range of these problems is diverging rather than converging. Engineers are busy designing new and complex machines, destined to operate not only in the prosaic world of our everyday lives but in hostile and exotic environments where man has never lived—from the crushing Stygian abysses of our oceans to the infinite voids of deep space. Literally millions of people are actively engaged in the business of designing and constructing machines and machine systems, but there are scarcely a thousand people who make it their primary business to study man in his intimate relations with these machines. For reasons such as these, man-machine problems appear to be multiplying faster than we can do research on them.

The practicing engineering psychologist finds that he spends a considerable portion of his time “trying things out.” In some industries and in some laboratories, experimentation of one kind or another may well take up the major part of the engineering psychologist’s working time. As one might suppose from the historical development of the field and the nature of the work, methodologies in engineering psychology are diverse and adapted from several disciplines (see Chapanis 1959). The discovery of new methodologies is also a topic of continuing and active interest in the literature of engineering psychology. For this reason the techniques mentioned below should be regarded as a sample of the ways in which problems have been answered in the past rather than as an exhaustive list of the tools available to the practitioner in this field.

Whenever he can, the engineering psychologist uses full-scale experimentation with the same rigor and sophistication that one expects of the best tradition of experimentation. Because of the complexity of his problems and the many variables that normally influence human behavior in machine situations, the engineering psychologist typically employs experimental designs using several variables, deriving, for example, from methods of analysis of variance. In addition, the psychophysical methods are widely used for obtaining useful data on sensory capacities, as are articulation test methods for measuring the effectiveness of speech communication devices and systems. In preliminary exploratory work on complex systems, the study of critical incidents, accidents, and near accidents has proven widely useful in locating potential sources of man-machine conflict.

From the industrial engineer, the engineering psychologist has borrowed and adapted a number of techniques for directly observing systems in operation. Some of these are activity sampling procedures, process analysis, and micromotion methods. Finally, from more conventional techniques of industrial psychology the engineering psychologist has adapted to his own needs methods of job analysis, task analysis, personnel requirement inventories, questionnaires, tests, and rating scales.

Subject matter

Almost everything that is known about man as a living, feeling, behaving organism is relevant to the engineering psychologist. Current thinking even extends to man as a social organism: a number of recent research findings show clearly that the effectiveness of complex man-machine systems is determined to a considerable extent by the compatibility of the team of men who work in the system. Examples are nuclear submarines and advanced space vehicles, where men are forced to live and work together for extended periods of time in cramped quarters while under unusual stress.

For all that, the amount of information about human behavior that may be required for particular applications varies enormously. In the design of a space vehicle, the engineering psychologist may be faced with problems that cover the full range of human psychology. He needs to consider the sensory capacities of operators as they relate to instrument displays and the sensing of information from inside and outside the vehicle. Knowledge about man’s ability to make rapid and correct decisions is vital. Working hours and work-rest cycles are certain to be different from those on earth, and it is important to know how well man can perform under these altered working conditions. The engineering psychologist also needs to consider the human ability to make correct control actions of a great variety. Human reactions to exotic environments, the ability to learn new and complex skills, emotional reactions and personality problems that might arise from the stresses of space flight, social behavior—all of these are relevant for the engineering psychologist. [See SPACE, OUTER.]

By contrast with the complexity of a space vehicle, there are many problems in engineering psychology that are much simpler and more circumscribed. The engineering psychologist who works with common consumer items may be faced with questions like: How should the controls be placed on a stove so that housewives correctly turn the correct control to activate a burner? What size and spacing of letters, numbers, and symbols should be used on the labels of household appliances so that they will be easily legible? How should the numbers and letters be arranged on push-button telephones? All of these are examples of relatively restricted but genuine problems encountered in the practical business of engineering psychology.

The man—machine model . In their work engineering psychologists regard man as an element in a man-machine system. Basically, a person who uses or operates a piece of equipment has to do three things. He has first to sense something and to perceive what this something means. The thing the human operator senses is termed a machine display. It may be any of a thousand different things—the position of a pointer on a dial, the print-out of a digital computer, a voice coming over a loudspeaker, a red light flashing on a control panel, a highway sign along a speedway, or the resistance felt in a certain kind of control.

Having sensed a machine output, the man next has to interpret what the display means, understand it, perhaps do some mental computation, and reach a decision of some sort. In so doing, the human operator often uses other important human functions—the ability to remember and recall, to compare what he now perceives against past experiences, to recall operating rules he may have learned during training, or to put what he now experiences into the context of strategies he may have formed for handling events such as this. A man is not necessarily aware that he is doing any or all of these things, of course. His behavior may be so well practiced and routine that the decision to do one thing or another may be made almost by reflex, just as the experienced driver may decide almost unconsciously whether or not he should stop when he sees a green traffic light change to yellow. All of the functions discussed in this paragraph are ordinarily subsumed under the heading of higher mental processes in textbooks of psychology. Engineering psychologists often use machine terminology instead of more familiar psychological terms and, in keeping with this trend, refer to all these higher mental processes collectively as data processing.

Having reached a decision about the information he has received through his sense organs and dealt with in his nervous system, the human operator then normally takes some action. The action is normally exercised on some sort of a control—a push button, lever, crank, pedal, switch, or handle. Man’s action upon one or more of these controls exerts in turn an influence on the behavior of the machine, its output and displays. Many times, of course, a machine operator monitoring a process may decide to do nothing. This is still regarded as an important human output.

A man-machine system does not exist in isolation but in an environment. The character of this environment influences man’s efficiency and performance, and the engineering psychologist is often vitally concerned with these factors. Among the more important environmental influences are such commonplace ones as temperature, humidity, ventilation, lighting, noise, and movement. Some less common but still important ones are vibration and a whole host of noxious gases and contaminants. In more exotic systems the engineering psychologist may also have to be concerned with the effects of increased acceleration, weightlessness (zero gravity conditions), anoxia caused by reduced oxygen at high altitudes, radiation, and the effects of reduced barometric pressures on the body.

The display of information. The man—machine model described above provides a convenient framework for summarizing the main content areas of engineering psychology. Machine displays, in a manner of speaking, represent the starting point of the man-machine cycle, for it is through such displays that the machine communicates to its human operator. For this reason, a considerable amount of work has been devoted to studies of displays and the ways in which they should be selected and designed. Although man has available a dozen or so sense channels that could conceivably be used to receive information from machine systems, only three—vision, hearing, and the sense of touch or vibration—have been exploited to any great extent.

In the area of visual displays, research has been done on such problems as the design of mechanical indicators; scales; cathode-ray tubes (radar scopes); charts, tables, and graphs; warning lights and signals; abstract visual dimensions (symbols varying in color, shape, brightness, or size) for coding information; and general and specialized lighting systems (for ready rooms and radar rooms).

Problems of auditory displays can be grouped into two broad classes: those dealing with tonal or noise signals (sirens, diaphones, horns, buzzers, bells, gongs, and so on), and those dealing with speech communication systems. Research on the former class of problems has been generally concerned with signal processing and control: the selection of signals and signal characteristics, the filtering of signals to eliminate unwanted or interfering noise, and the use of signals for coding information. Research on speech communication systems has been aimed at the design of special or efficient languages, the design of the components of speech communication systems (microphones, amplifiers, and so on), and the design of speech communication systems as a whole. [See HEARING; PERCEPTION, article on SPEECH PERCEPTION; VISION.]

Machine displays for senses other than vision and hearing have not been used very much, and perhaps for this reason, research on such displays is relatively meager. Within recent years, however, it has been shown that the vibratory sense can be used for an efficient communication system. Using a special kind of vibratory code applied to a man’s chest, Geldard (1957) trained one subject to receive up to 38 words per minute. However, because of the awkwardness of the equipment and the possibility of interference from other sources of vibration, it is doubtful whether that particular system will be put into any operational situation. This research shows, however, that there may be unexplored possibilities for communication through these other senses.

Data processing. One important function which man serves in many man-machine systems is that of data processing. He may be required to perceive things, assimilate large masses of data, evaluate or assess a situation, do computations, and make decisions. Despite much research on these higher mental processes our understanding of the mechanisms by which people do these things is still imperfect. As a result, it is in this area of engineering psychology that one finds the fewest principles and concrete recommendations about the ways in which man can be best integrated into man—machine systems. As more and more systems become automated, however, man’s role in the system becomes more and more that of a monitor and decision maker. One may expect therefore that some of the greatest research gains are yet to be realized in this area.

Machine controls. Research on the design of machine controls has yielded a substantial number of useful and practical principles. These are concerned with such things as the factors involved in selecting the correct control for a job, control-display ratios, direction-of-movement relationships, control resistance, ways of preventing accidental activation, and control coding. Among the more complex kinds of controls are those involved in what are called closed-loop tracking systems. (Driving a car along a winding road is a simple example of a closed-loop tracking task.) Research on the last kind of problem involves considerations of the mathematical relationships between the movements of the control and the dynamics of the system.

Environmental problems. Although the study of environmental problems might seem to fall exclusively within the province of the applied physiologist, the fact is that psychologists have studied the effects of a wide range of environmental factors on gross behavior. These studies have been concerned with problems of illumination, noise, anoxia (lack of oxygen at high altitudes), certain kinds of noxious gases and contaminants, heat and cold, vibration, and most recently, weightlessness.

The aim of research . In common with research in most other areas of science, research in engineering psychology has as its first aim understanding. Beyond this, however, the engineering psychologist hopes that his researches will yield principles which can be put into the form of definite recommendations for machine design. A large number of these are now available, and they can be found in textbooks and guides on this subject (see, for example, Chapanis 1965; McCormick 1957; Morgan et al. 1963). The following example from research on control design will illustrate one of the concepts that originated in engineering psychology and some of the design recommendations that followed from it.

The results of control movements are often shown on a display. The tuning knob on a radio is a familiar example. As you turn the tuning knob, you change a variable condenser inside the radio. At the same time, a pointer moves along a linear or circular scale to show you what frequency or wave length the radio has been tuned to. Examples of linked controls and displays are common in the world of machines. The controls may be knobs, cranks, levers, or translatory controls. Sometimes a control may be in one plane (for example, on the horizontal working surface in front of an operator) and the display in another plane (for example, directly in front of the operator’s eyes and at right angles to the surface on which the control is mounted). The number of permutations of controls, displays, and orientations is, of course, very great.

In the case of many control-display combinations it turns out that most people have consistent expectations about the way in which a control should move in order to produce a change in the display. When these expectations are strong and found universally, they are called population stereotypes. Controls that conform to these population stereotypes are responded to much more quickly and with far fewer errors than are controls that do not. Human beings are remarkably adaptable and, given sufficient training, can learn to use controls and displays that do not agree with population stereotypes. The interesting thing, however, is that if such an operator is subjected to great stress or to an emergency situation, he frequently regresses or reverts to his natural expectancies. Many accidents in aircraft have been traced to this single factor alone. The design recommendation which follows from this research is clear: Whenever strong population stereotypes exist, control and display movements should agree with them.

Man-machine system design

Although, as was remarked earlier, the scope of engineering psychology covers a range from relatively simple devices to enormously complex machine systems, it is the latter which are the most challenging, most complex, and most difficult to deal with. The design of an air traffic control system, an automated mail handling system, a new guided missile system, or a deep space vehicle system is a problem of gigantic proportions. Thousands of technical and professional experts of a hundred or more different varieties may work for years to bring such a large system into being. Engineering psychologists are generally recognized as important members of such design teams.

In the preceding section the subject matter of engineering psychology has been presented from the standpoint of the way it is organized by the psychologist himself. When we look at the field from the standpoint of what the engineering psychologist contributes to the design of man-machine systems, a somewhat different order of topics results.

Design and planning . The first step in the creation of any large system is generally called a study phase. It is at this time that engineers study in detail the specifications and requirements of the system. Alternative ways of designing the system to meet the requirements are thought up, tested, tried out, and discarded, modified, or accepted. Contrary to what many lay people think, there is much trial and error involved in this stage of the process, and the final conceptualization of the system may be quite different from initial ideas. During this study phase, engineering psychologists are called upon to study and decide about man’s role in the system. They usually assist in making decisions about precisely which functions of the system should be allocated to humans and which to machine components. They prepare estimates of the number and types of people that will be required to man the system when it is completed, the so-called QQPRI (Qualitative and Quantitative Personnel Requirements Information). If personnel with specialized training will be needed, engineering psychologists plan and design training programs and curricula to ensure that qualified people are available to operate the system when it is completed. Finally, they may try to anticipate the social consequences of the system on its human operators or society in general.

Project engineering . After preliminary designs and plans have been completed, the system goes into actual construction. The first model of any large system is seldom built as originally planned. Difficulties appear at this point which had not been anticipated in the largely paper-and-pencil study phase, and the changes and modifications that must be made often number in the thousands. During the production phase of system design the engineering psychologist usually makes substantial contributions to the man-machine combination, although ultimate responsibility for design usually rests with an engineer. The engineering psychologist studies, tests, and makes recommendations about specific workplace arrangements, solves specific problems of display and control, and makes design recommendations about the solution of environmental problems.

Another important task of the engineering psychologist is that of studying the system from the standpoint of its reliability and maintenance and of anticipating special problems of maintenance. With the increase in the number of highly automated systems, problems of faultfinding and maintenance are becoming increasingly important. For one thing, the cost of a highly automatic system is so great that the user cannot afford to have it idle for long periods of time. At the same time, such systems are so complex that it is becoming increasingly difficult for repairmen to diagnose what is wrong with them and decide how they can be most quickly repaired. As one illustration of the magnitude of the problem, the U.S. Air Force estimates that to repair and maintain a typical system (for example, an aircraft) during its normal lifetime may cost up to ten times the original purchase price of the system. Further, of the total time spent in actively repairing most large systems, as much as 80 per cent of a maintenance man’s time is spent in merely discovering what is wrong with it. The engineering psychologist’s contributions here are in planning effective faultfinding strategies and in seeing to it that the equipment is so designed (with sufficient test points, accesses, and so on) that it can be easily maintained, that it is installed where it can be readily reached, that appropriate, well-written maintenance manuals are ready as soon as the equipment is completed, that special tools and test equipment are properly designed and constructed, that maintenance men are trained, that adequate work and storage facilities are provided, and that an adequate supply of spare parts and replacements is provided.

The end result of this part of system development is what is usually termed a prototype, a first full-scale working model of the system.

Test and evaluation and operational use . Once a protoype of a system is constructed, it usually goes through a series of tests, often termed operational suitability tests or evaluations, to discover if the system really does what it is supposed to do. It is generally recognized that a man-machine system has to be tested as a complete entity and that the human components in a system may make or break it. The problems of testing systems that contain people are far more difficult than conducting simple engineering or physical tests. Because of their special training in experimental methodology and in the problems of conducting studies on people, engineering psychologists are often given major responsibility for the design and conduct of such tests.

When a large system has been tested, accepted, and put into operational use, it may undergo still further modifications as experience with it accumulates. These are usually far fewer in number and less sweeping than those which occur earlier in the design. Although the engineering psychologist may still play some role in this stage of the lifetime of the system, it is usually a much less important one than in earlier design phases. It is at this time that the training and personnel specialist replaces the engineering psychologist in terms of importance.

Alphonse Chapanis



Chapanis, Alphonse 1959 Research Techniques in Human Engineering. Baltimore: Johns Hopkins Press.

Chapanis, Alphonse 1965 Man-Machine Engineering. Belmont, Calif.: Wadsworth.

Geldard, Frank A. 1957 Adventures in Tactile Literacy. American Psychologist 12:115-124.

Gilbreth, Frank B. 1909 Bricklaying System. New York: Clark.

Mccormick, Ernest J. (1957) 1964 Human Factors Engineering. 2d ed. New York: McGraw-Hill. → First published as Hitman Engineering.

Morgan, Clifford1. <* al. (editors) 1963 Human Engineering Guide to ^^^ipment Design. New York: McGraw-Hill.

Taylor, Frederick W. (1898)1911 Scientific Shoveling. Wyoming, Pa.: The Wyoming Shovel Works.

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