Z94.9 Human Factors (Ergonomics) Engineering

The Human Factors Subcommittee’s task was made considerably easier due to the work of previous subcommittees.  Earlier editions of this book served as a substantial base for this latest revision.  The names of previous subcommittee members can be found in previous editions of this book.  We appreciate their efforts.

The Human Factors Subcommittee has put forth considerable effort in revising and updating this chapter.

Subcommittee members consisted of the following members:


Alex Kirlik, Ph.D.
School of Industrial and Systems Engineering
Georgia Institute of Technology


Arthur D. Fisk, Ph.D.
School of Psychology
Georgia Institute of Technology
Richard Henneman, Ph.D.
NCR Human Interface Technology Center


Steven A. Lavender, Ph.D.
Department of Orthopedic Surgery
Rush-Presbyterian-St. Luke’s Medical Center, Chicago


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ABDUCTION. Movement of a limb away from midline axis of body.

ABSOLUTE PITCH. Refers to the ability of a person to identify the pitch of a pure tone without any external reference.

ABSOLUTE THRESHOLD. That stimulus value which marks the transition between no response and response on the part of an observer; occasionally used analogously to describe a qualitative change in the nature of the response, as the “threshold of feeling” between sound and pain at intense levels of acoustic stimulation; or the “pricking pain threshold” between perceived warmth and burn. Values obtained for the threshold depend on the statistical properties of the psychophysical method used.

ABSOLUTE THRESHOLD. A rating of the passage space available for a person to reach his/her work station based on the width of the passageway. The rating is multiplied by the number of people affected and averaged across people.

ACCIDENT. Any event caused by human situational and environmental factors or combinations of those factors which interrupt the work process and which may or may not result in injury, death, property damage, or other undesired events but which has the potential to do so.

ACCOMMODATION. The adjustment of a sense organ to receive an impression distinctly. In vision, the ability of the eye to focus on objects at varying distances effected by the gradual thickening and increasing curvature of the crystalline lens as objects become closer.

ACCURACY. A human performance measure indicating the correctness of behavior as measured against an objective or normative standard.

ACOUSTIC SCATTERING. The irregular reflection, refraction, or diffraction of a sound in many directions.

ACOUSTIC (OR AUDITORY) STIMULUS. The waveform of air pressure at the eardrum.

ACOUSTIC TRAUMA. Injury to the ear caused by an intense auditory stimulus resulting in a certain degree of temporary or permanent hearing loss.

ACTIVITY ANALYSIS. A structural listing of the operations, behaviors, or tasks that make up a job or work. Data gathered typically includes the sequence, frequency, and importance of activities and the time devoted to each, as well as their interrelationships. Various procedures and formats are used, according to the purpose of the analysis. (See ACTIVITY SAMPLING.)

ACTIVITY SAMPLING. Performing an activity analysis by observing only portions or segments of the ongoing work process, with observation periods being scheduled in advance according to a sampling rationale. (See ACTIVITY ANALYSIS.)

ACUITY. A measure of the ability to resolve or discriminate sensory stimulation.

ADAPTATION, GENERAL. An adjustment internal to a behaving system to maintain stable or more successful relationships with an external environment.

ADAPTATION, SENSORY. The maintenance of sensory effectiveness under changing stimulation (positive adaptation) or the reduction of sensory responsiveness with continued stimulation (negative adaptation); for example, maintenance of visual acuity under reduced illumination, or reduced responsiveness to an unpleasant odor.

ADAPTIVE CONTROL. Form of system control in which the control law changes as a function of time-varying dynamics of the controlled system.

ADDUCTION. Movement of a limb toward midline axis of body.

ADVISORY LIGHT. A signal indicating safe or normal performance, operation of essential equipment, or to alert an operator for routine action purposes.

ADVISORY SYSTEM. Form of human operator aiding in which automation, such as an expert system, provides recommended courses of action to the human operator.

AFFORDANCE. A description of an object in terms of the actions it makes available.

AFTERIMAGE. A visual image or other sense impression that persists after the stimulus is no longer operative. Visual after-images are complex perceptions that can vary in hue, brightness, saturation, shape, pattern, texture, focus, latency, duration and developmental sequence.

ALARM. Device indicating (typically undesired) deviation of the state of a controlled system from a nominal or expected value.

ALPHA. Probability of Type I error; i.e., the probability of incorrectly rejecting a null hypothesis.

ALPHA TESTING. First phase of software evaluation involving limited product release.

ALPHANUMERIC DISPLAY. Display consisting solely of numbers and letters.

ANALOG DISPLAY. Display format in which a quantity is represented by a physical dimension of a display; e.g., a clock.

ANECHOIC ROOM. A room in which boundaries absorb almost all incident sound resulting in virtual free field conditions.

ANIMATED-PANEL DISPLAY. Diagrammatic representation of components of a system hardware and/or simple semi-functioning models of such components.

ANOXIA. Lack of oxygen in the blood stream or tissue cell. Although the result of many mechanisms, the ultimate effect frequently is defective function of many sensory and motor functions. Produced environmentally by high altitude, chemically by pollutants and drugs, or locally by overexertion. May result in death.

ANTHROPOMETRY. Classically, the study of people in terms of physical dimensions. (1) The measurement of static and dynamic features or characteristics of the human body. Typically included are linear and arc dimensions, mass and volume. (2) The techniques used to quantitatively express the form and dimensions of the body. (See Z94.2 ANTHROPOMETRY & BIOMECHANICS.)

APPARENT MOTION. A sensory or perceptual illusion in which stationary stimuli are perceived to be moving.

APPLICATION. Computer software dedicated to a particular task.

ARTICULATION INDEX (AI). A numerically calculated measure of the intelligibility of speech in the presence of background noise. It is generally based on the speech/noise ratio for each of twenty frequency bands. This ratio is weighted, multiplied by .05, and summed over the twenty bands to yield the AI which ranges from 0.0 (voice communication nearly impossible) to 1.0 (excellent communication).

ARTIFICIAL HORIZON. A pictorial display used in aircraft to provide information as to the orientation of the plane with respect to the horizontal, indicating to the pilot whether he/she is flying straight and level.

ARTIFICIAL INTELLIGENCE. The study of the use of computers to perform tasks that are consensually agreed to display aspects of intelligence, rationality, or adaptation.


ATTENTION. Allocation of sensory, perceptual and cognitive functionality to stimuli or information processing tasks.

ATTENTION, DIVIDED. Allocation of attention among two or more concurrent tasks.

ATTENTION, SELECTIVE. Ability to focus on a desired set of information or a task, to the exclusion of the remaining set of information or competing tasks.

AUDIOGRAVIC ILLUSION. Errors in auditory localization which accompany an error in the perception of body position.

AUDIOGYRAL ILLUSION. Errors in auditory localization following rapid rotation of the body in the absence of visual cues.

AUDIOMETER. Instrument used to assess human auditory sensitivity as a function of frequency. Tones of varying frequencies and intensities are presented through earphones to a subject who indicates the point at which a given tone just becomes, or ceases to be, audible.

AUDITORY AFTER-EFFECT. A phenomenon lasting several seconds in which familiar sounds are modulated following listening to rapid, high-intensity pulses for about one minute.

AUDITORY FATIGUE. A temporary increase in auditory threshold due to a previous auditory stimulus.

AUDITORY FLUTTER. A wavering auditory sensation resulting from the periodic interruption of a continuous sound at a sufficiently slow rate.

AUDITORY FUSION. A phenomenon in which a series of short duration primary sounds with successive arrival times at the ear(s) produce the sensation of a single secondary sound.

AUDITORY LATERALIZATION. The determination by a subject that the apparent direction of a sound is either left or right of the frontal-medial plane of the head.

AUDITORY LOCALIZATION. The determination by a subject of the apparent direction and/or distance of a sound.

AUTOKINETIC EFFECT. An illusion of the apparent movement of a stationary point light source presented in a dark stimulus field in the absence of a visual frame of reference.

AUTOMATION. The use of electromechanical or information technology to perform autonomous functions.

AUTOMATICITY. A psychological construct denoting a combination of information processing characteristics, including processing that is fast, reliable, unlimited by short term memory capacity, robust to increase in task difficulty, and difficult to modicy once learned.

AVAILABILITY (2). A cognitive heuristic in which the likelihood of an event is judged by the ease with which examples of the event can be generated or recalled.

AVAILABILITY, MEASURE OF. The ratio of the total time a system is capable of performing its function to the total time that there is a requirement for its operation.

“AVERAGE MAN” CONCEPT. An oversimplified method of describing the characteristics of a varied population based on mean measurements. When more than one measurement is used the “average man” disappears.


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