Most human factors/ergonomics problems are well described by a systems approach. The model below considers an environment-operator-machine system.

The Operator is the main focus in HFE/Ergonomics and should be described in an organizational context. For example, we may study the effect of environmental factors and machine design features on operator performance. The design features of the machines (such as different controls and displays), and of the environment (such as noise and heat) are independent variables that we can manipulate through design, and the operator measures are dependent variables. The dependent variables include measures of negative and positive outcome and satisfaction. One may measure operator performance, such as the time to assemble a car, or one may measure the number of errors committed by the operator, or one may ask the operator about the new design – how good it is and how satisfying it is to work with.

The operator perceives the environment - mainly through the visual and auditory senses, then considers the information, makes a decision and finally produces a control response. Perception is guided by the operator’s attention. From the millions of bits of information available, the operator will attend to the information that would seem relevant to the task. For new or unusual tasks decision making can be time consuming. The operator will have to interpret the information, the alternatives for action, and to what extent those actions are relevant to achieve the goals of the task.

The purpose of the operator's response is to convey information through either manual response, such as control of a machine (e.g. computer) or a tool (e.g. hammer) or an artifact (e.g. football) or verbal response to a co-worker. For some technology, verbal response may also used in controlling the machine (e.g. through speaking).

There are several modulating variables that affect Task performance, including: operator needs, attitudes, competence, expertise, motivation, age, gender, body size and strength. These are idiosyncratic variables and they differ between individuals. For example, an experienced, competent operator will perceive a task differently than a novice operator. The former/experienced operator will focus on details of importance, filter irrelevant information and “chunk” the information into larger units, so that it is possible to make faster and more efficient decisions. A novice operator, on the other hand, may not know where to look for important information, and may think the work is very stressful. Another modulating variable is body size. Different body dimensions have consequences for the design of workstations.

Stress is an important variable that affects perception, decision making, and response selection. High psychological stress levels are normal when the time to perform a task is limited, or when there is too much information to process. Under such conditions the bandwidth of attention may narrow, thereby the probability of operator error increases. In general, high stress levels lead to increased physiological arousal, which can be measured using various physiological measures (e.g. heart rate, EEG, blink rate). These would then be dependent variables for monitoring of stress.

The sub-system Environment is used to conceptualize the task as well as the context in which it is performed. It could be a car assembly operator monitoring a robot at work. Here the organization of work determines the task allocation; some tasks may be allocated to fellow workers, or supervisors, or computers. Task-allocation is a central problem in ergonomics: How can one best allocate work tasks among machines and operators so as to realize both company goals and individual goals? Task allocation affects how information is communicated between employees and computers, and it also affects system’s performance.

The operator receives various forms of feedback from his/her actions. There may be feedback from task performance, from co-workers, from management and so forth. To enhance task performance, communication, and job satisfaction, such feedback must be informative. This means that individuals must receive feedback on how well or poorly they are doing, as well as feedback through communication.

The ambient environment describes the influence of environmental variables on the operator. For example, a car assembly-worker is exposed to high levels of noise and heat. This increases physiological arousal and stress, thereby affecting task performance, safety and satisfaction.

The importance of the organizational environment has been increasingly emphasized during the last few years. Work is undertaken in an organizational context, which deeply affects the appropriateness of alternative design measures. Company policies with respect to communication patterns, decentralization of responsibilities, and task allocation have an impact on ergonomics design. One should first decide who should do what and how people should communicate. Following this activity, individual tasks, machines, displays and controls can be designed.

The Machine sub-system is broadly conceptualized in the above model. The term “machine” could be a computer, a video recorder (VCR), or a football. The term “controls” denotes machine controls which are used by the operator. In some systems, machine control may be taken over fully or partially by automation and computers.

As a result of machine control, there is a changing state which is “displayed”. It can be seen or heard; a pocket calculator will show the results of a calculation, the melting iron in a steel plant will change temperature and color, a computer will produce a sound, and the toaster will pop the bread. All of these are examples of displays. They convey visual or auditory information, and they can be designed to optimize systems performance.

It is important to note that the system in the model has feedback. Machine information is fed back to the environment subsystem and becomes integrated with the task. Ergonomics is concerned with dynamic systems ? it is necessary to go around the loop and incorporate the effect of feedback.

For more information, see Helander, M. (in print). Guide to Human Factors and Ergonomics, CRC Press