Z94.9 Human Factors (Ergonomics) Engineering

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TABULAR DISPLAY. Display of alphanumeric and other symbols in a row and column format.

TACHISTOSCOPE. An experimental device for controlling the exposure of visual stimulus material, e.g., symbols.

TACTILE. Of or relating to the sense of touch. Tactual.

TACTILE CONTROL. Control regulated through tactile sensory feedback (q.v.). It may be reinforced by designing equipment controls to incorporate distinctive texture patterns (e.g., knurling) or shapes to prevent error. Other means of tactile control are the initiation of movement with a vibratory cue and termination through a positive stop. (See TACTILE SENSE, TACTILE STIMULUS.)

TACTILE SENSE. The sense of touch. Experienced through four types of mechanoreceptors (q.v.) located throughout the body. Significant source of sensory feedback (q.v.). Improper clothing (thick gloves) may impair tactile sensation and cause inaccurate discrimination of tactile signals. (See TACTILE CONTROL, TACTILE STIMULUS.)

TACTILE STIMULUS. An input originating in the touch mechanoreceptors (q.v.) as sensory end organs (q.v.). The input is converted into a nerve signal for afferent transmission along the sensory nerves (q.v.) to the brain or spinal cord, whence an efferent signal is transmitted along a motor nerve (q.v.) causing muscular reaction. Tactile stimuli in the workplace replace other cognitive judgment and are conducive to quick error-free control action. (See TACTILE SENSE, TACTILE CONTROL.)

TARGET. (1) Any object, point, etc., toward which something is directed. (2) An object which reflects a sufficient amount of a radiated signal to produce an echo signal on detection equipment.

TARGET ACQUISITION. The process of optically, mechanically, or electronically orienting a tracking system in direction and range to lock on a target.

TARGET DISCRIMINATION. (1) Perceiving a desired signal within a background of noise. (2) Distinguishing multiple signals.

TASK. A group of related job elements performed within a work cycle and directed toward a goal; a composite of the discriminations, decisions, and motor activities required of an individual in accomplishing a unit of work. 

TASK ANALYSIS. An analytical process employed to determine the specific behaviors required of human components in a human-machine system. It involves determining, on a time base, the detailed performance required of human and machine, the nature and extent of their interactions, and the effect of environmental conditions and malfunctions. Within each task, behavioral steps are isolated in terms of the perceptions, decision, memory storage, and motor outputs required, as well as the errors which may be expected. The data are used to establish equipment design criteria, personnel and training requirements, etc.

TASK CODING. A numerical and/or alphabetical index sometimes used during task analysis to indicate in relative terms: a) how demanding a task is with respect to perceptual, judgmental, and motor skills (Skill Coding); b) how critical the correct performance of the task is to system performance or mission success (Task Criticality); c) whether personnel are already doing the task or whether it is new (Task Newness).

TASK, CONTINUOUS. Those tasks which involve a continuously changing response to a continuously changing stimulus. The operator compares the desired output with the error signal which is fed back and makes continuous adjustments accordingly; e.g., maintaining a given vehicle attitude by manual control movements in response to instrument indications.

TASK ELEMENT. A basic unit of behavior, made up of the smallest logically definable set of perceptions, decisions, and responses which the human being is required to perform in completing a task; e.g., a single action identified by a specific signal on a specified indicator or display, a specific control actuation, and a feedback signal or response adequacy.

TASK EQUIVALENCE. The condition existing when two tasks have sufficient elements in common to permit an individual to transfer from one to the other at the same level of skill without additional training or experience.

TASKS, PROCEDURAL. Those tasks which involve stepwise, discontinuous, or all-or-none responses to discrete perceptual cues. The operator observes a displayed condition and performs a single response, or observes a series of conditions and performs a series of separate nonrepeated responses; e.g., turning on deicing equipment when icing conditions are indicated.

TELEOPERATION. The remote control of a teleoperator such as a robot, typically accomplished via transmitted video information.

THRESHOLD, ABSOLUTE VISUAL. The minimum intensity of light that can be seen by the human eye after complete dark adaptation, generally considered to be about 1/1,000,000,000 of a lambert in the periphery. Theoretically, as few as six quanta of light reaching the retina have a good probability of yielding a visual sensation.

THRESHOLD CONTRAST. The smallest difference between luminances (or brightnesses) that is perceptible to the human eye under specified conditions of adaptation luminance and target visual angle. Also called contrast threshold, liminal contrast. Compare threshold illuminance. Psychophysically, the existence of a threshold contrast is merely a special case of the general rule that for every sensory process there is a corresponding lowest detectable intensity of stimulus, i.e., a limen.

THRESHOLD, DIFFERENCE. The minimum difference between two stimuli that can be perceived as different; statistically, that difference which is perceptible 50% of the time.

THRESHOLD (LIMEN). The statistically determined point at which a stimulus is just barely adequate to elicit a specified organismic response (absolute threshold) or at which it differs enough from another stimulus to elicit a different response (difference or differential threshold).

THRESHOLD, MASKED DIFFERENTIAL. The least amount of change of a stimulus necessary to elicit a response when the stimulus is obscured (masked) by another stimulus presented simultaneously; applies to brightness, loudness, etc.

THRESHOLD OF AUDIBILITY. For a specified signal, the minimum effective sound pressure level of the signal that is capable of evoking an auditory sensation in a specified fraction of the trials. The characteristics of the signal, the manner in which it is presented to the listener, and the point at which the sound pressure level is measured must be specified. Also called threshold of detectability.

THRESHOLD OF DETECTABILITY. Threshold of audibility.

THRESHOLD OF DISCOMFORT. In acoustics, for a specified signal, the minimum effective sound pressure level of that signal which, in a specified fraction of the trials, will stimulate the ear to a point at which the sensation of feeling becomes uncomfortable. The term applies similarly for other senses.

THRESHOLD OF PAIN. A specified stimulus signal, the minimum level of that stimulus which, in a specified fraction of trials, will stimulate a sense organ to a point at which the discomfort gives way to definite pain that is distinct from mere nonnoxious feeling of discomfort.

THRESHOLD SHIFT. A threshold shift is a change in the threshold of audibility for an ear at a specified frequency. The amount of threshold shift is customarily expressed in decibels.

THRESHOLD, TERMINAL. A maximum stimulus that will produce a given type of sensory experience or elicit a given kind of response.

THROUGH-PUT CAPACITY. The output of thoroughly processed items from a machine.

TIMBRE. That attribute of auditory sensation by which a listener discriminates between two sounds of similar loudness and pitch, but of different tonal quality.

TIME AND LINK ANALYSIS. An analysis of the number and duration of activities assigned to each potential element of a system. It provides an overview of what the human component is expected to do at each point in an operation, an outline of the process of information exchange among operators and between operators and equipment, and data useful in the determination of crew size for each major component of the system.

TIME-LINE ANALYSIS. An analytical technique for the derivation of human performance requirements which provides an indication (by means of a time-line chart) of the functional and temporal relationships among tasks, as well as the behavior and task loadings for any given combination of tasks.

TIME-SHARING. The division of an operator’s perceptual, decision-making, or response time among activities or tasks which must be performed at or about the same time. For example, flight control movements must be time-shared with engine control adjustments, communications, etc; in general, tasks which must be time-shared in the operational situation should also be time-shared during training.

TINT. Any color lighter, i.e., of higher lightness, than median gray. May imply weak saturation as well as relatively high lightness.

TONAL GAP. A gap is a frequency band of low auditory sensitivity above and below which the sensitivity is better.

TONAL ISLAND. A tonal island is a frequency region bonded above and below by tonal gaps.

TONALITY (TONAL). Tonality is the phenomenon in which tones spaced an octave apart sound more alike than those spaced along any other interval.

TONE. (1) Physics-—a sound wave capable of exciting an auditory sensation having pitch. (2) Psychology—a sound sensation having pitch.

TOUCH SCREEN. An input device consisting of a screen sensitive to either the position or pressure of an object pressed against the screen.

TRACKBALL. An input device consisting of a ball resting in a socket, which can be rotated by a user to control cursor position.

TRACKING. The process by which an operator continually attempts to minimize some measure of the difference between a desired and an actual output of a system; an activity that involves following a target moving in two- to three-dimensional space with reference to the observer or equipment.

TRAINING. The totality of instructions, planned circumstances, and directed activity by which personnel acquire and/or strengthen new concepts, knowledge, skills, strength habits, or attitudes which will enable them to perform assigned duties with maximum reliability, efficiency, uniformity, safety, and economy.

TRANSFER OF LEARNING. The phenomena through which information acquired in one situation is applied or “transferred” to some other situation, most usually an operational one.

TRANSILLUMINATION. (1) Indirect illumination used on console panels and utilizing edge- and back-lighting techniques on clear, fluorescent, or sandwich-type plastic materials. (2) Transmitting light through material to enhance seeing quality deviations.

TRANSMITTANCE. The ratio of luminous flux transmitted through a medium to the incident flux, expressed as a percentage. “Selective transmittance” refers to the transmission of particular wavelengths of light through a transparent or translucent medium, such as a red filter.

TREMOR. Shaking, trembling, or oscillation which may result from natural impairment or from excitement, emotion, cold, or an effort to maintain a part of the body in a fixed position. It can be measured by the distance or the number of departures from a fixed path or position in a given time. Fatigue or efforts to prevent tremor may increase it; strong support of the body or part of the body affected, or the application of friction, tend to decrease the trembling.

TRIAL. A trial is a sequence of events during an experimental session in which a subject (or subjects) is presented a stimulus set and the resulting response set is recorded.

TRIANOMALY. Rare type of trichromatism in which an abnormally large portion of blue stimulus is required in a blue-green mixture to match a given cyan.

TRICHROMATIC THEORY. A color theory based upon the facts that all hues may be derived from the mixture of two or more of three primaries.

TRICHROMATISM. Form of vision yielding colors which require in general three independently adjustable primaries (such as red, green, and blue) for their duplication by stimulus mixture.

TRITANOPIA. Form of dichromatism in which reddish blue and greenish yellow stimuli are confused. Tritanopia is a common result of retinal disease, but in rare cases may be inherited. Sometimes called blue blindness.

TRUNK. Human body torso.

TURNAROUND TIME. That element of maintenance time needed to service or check out an item.


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