Z94.9 Human Factors (Ergonomics) Engineering

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RADIALE HEIGHT (ELBOW HEIGHT). Vertical distance from the floor to radiale, the depression at the elbow between the bones of the upper arm (humerus) and forearm (radius); subject standing erect, arms hanging naturally at sides. (See Z94.2 ANTHROPOMETRY & BIOMECHANICS.)

RATE TRACKING. A task in which the operator moves a control in such a way as to keep an indicator in line with a moving object, thus measuring the object’s speed of motion; involves an exponential relationship between system error and control movement. (See POSITION, TRACKING; TRACKING.)

REACTION TIME (RT). The interval between application of a stimulus and the beginning of the subject’s response (sometimes measured to response completion).

REACTION TIME, COMPLEX. The time required to react when a discrimination needs to be made; e.g., a response is made to one, but not to others, of two or more expected signals (discrimination reaction time), or a different response is specified for each kind of stimulus (choice reaction time).

REACTION TIME, SIMPLE. The time required to make a predetermined response as quickly as possible to prearranged signal; a combination of sensing time and response time.

REAL TIME. The absence of delay, except for the time required for the transmission by electromagnetic energy, between the occurrence of an event or the transmission of data, and the knowledge of the event, or reception of the data at some other location.

RECEIVER-OPERATING-CHARACTERISTIC. A receiver-operating-characteristic is a graphical summary of the performance of a detector. Detection probability is plotted on the ordinate and false alarm probability is plotted on the abscissa. These are conditional probabilities, that is, the probability that the condition (signal present or signal absent) is true. A family of non-intersecting curves is often plotted with either constant detectability index or constant signal-to-noise ratio as the parameter. Each curve shows how detection probability and false-alarm probability vary monotonically as a function of the decision criteria (operating point) of the detector.

RECEPTOR. A sensory nerve ending or end-organ in a living organism that is sensitive to physical or chemical stimuli.

RECOGNITION. The psychological process in which an observer so interprets stimuli received from an object that he forms a correct conclusion as to the nature of that object.

RED-GREEN BLINDNESS. A common form of partial color blindness, or dichromatism, in which red and green stimuli are confused because they are seen as various saturations and brightnesses of yellow, blue, or gray.

REDOUT. The condition occurring under negative g in which objects appear to have red coloration due to uncertain causes, possibly venous congestion of engorged eyelids.

REDUNDANCY. The existence of more than one means of accomplishing a given function. Each means of accomplishing the function need not necessarily be identical. (Active)—that redundancy wherein all redundant items are operating simultaneously rather than being switched on when needed. (Sometimes referred to as parallel redundancy.) (Standby)—the redundancy wherein the alternative means of performing the function is inoperative until needed and is switched on upon failure of the primary means of performing the function.

REFLECTANCE. The ratio of the reflected incident light which on striking a surface is reflected. Although lighting at the workplace is important, reflectance is more significant because it provides the visual input to the worker. Reflectance is expressed as a percentage of incident flux density.

REFRACTORY PERIOD. A brief period following stimulation of a nerve or muscle during which it is unresponsive to a second stimulus; may be absolute (no response) or relative (response only if the stimulus is very strong.)

REHEARSAL. The psychological process of repeating information in working memory for maintenance.

REINFORCEMENT. The action of a symbolic or concrete reward upon a response so that the response is strengthened (positive reinforcement); or, the action of symbolic or physical punishment on a response so that the response is weakened or replaced by an escape or avoidance response (negative reinforcement).

RELIABILITY. The probability that a system will perform a required function under specified conditions for a specified period of time or at a given point in time.

RELIABILITY (PSYCHOLOGICAL TEST). The complex property of a series of observations or measuring instruments that makes possible the obtaining of similar results upon repetition.

REMOTE HANDLING. Process by which manipulative skills are transferred from the proximity of the human operator to a more distant area by means of mechanically or electronically linked remote-control systems.

REMOTE INDICATING. Of an instrument, displaying indications at a point remote from its sensing element, often by electrical or electronic means.

REPRESENTATIVENESS. A cognitive heuristic in which the probability that a item belongs to a particular class is judged by the similarity of the item to the prototype member of the class.

RESOLVING POWER. The capability of the eyes to see two objects viewed simultaneously as two distinct objects; the capability to perceive as distinct two objects, in close proximity, casting images on the retina.

RESPIRATORY QUOTIENT. Quotient of the volume of CO2 produced, divided by the volume of O2 consumed by an organism, an organ, or a tissue during a given period of time.

RESPONSE. (1) Physiological--—the muscular contraction, glandular secretion, or other acti-vity of an organism which results from stimulation. (2) Psychological—a behavioral action, most commonly motor or verbal, that occurs following an external or internal stimulus.

RESPONSE TIME. The time required for a human operator to make a given response after a stimulus is perceived. Under simple conditions (e.g., pushing a button), it may be a few hundredths of a second.

RETINA. The inner liner of the eye which contains optic end organs. Composed of rods, cones (q.v.) and photosensitive cells, it translates light energy into nervous impulses.

RETINAL DISPARITY. The difference which exists between the images formed in the right and left eyes when a solid object is viewed binocularly.

RETINAL FIELD. The extended mosaic of the rod and cone receptor elements of the retina, which forms something of an anatomical correlate of the stimulus field.

RETINAL ILLUMINANCE. The illuminance of the retina, the usual units being the troland and the lux.

RETINAL RIVALRY. Alternation of sensations first from one eye and then from the other, when the two eyes are simultaneously stimulated by different colors or figures. Also called binocular rivalry. Contrast with binocular fusion, in which the two impressions are fused into a single impression.

RHODOSPIN. A substance found in the rods of the dark-adapted eye, which bleaches rapidly on exposure to light, and is converted to opsin and retinal.

RODS. Photosensitive cells of the retina which are specifically reactive to dim light. They are black-and-white sensitive only, and their proper function is required in poorly illuminated or night-vision applications.

ROOT MEAN SQUARE PRESSURE OF FUNDAMENTAL SPEECH SOUNDS. A method of relating the measurements of individual sounds as uttered, by making the intervals of time over which the squared pressures are averaged correspond directly to the intervals during which the specific vowels and consonants are spoken. Values are expressed in decibels relative to the r.m.s. pressure of the weakest speech sound (the initial consonant, “th,” of “thin”).

ROTATION (ZERO G). The controlled movement of a free-floating orbital worker to achieve a desirable work position after translation from one location in space to another; a positioning maneuver required in order to perform maintenance or other duties inside or outside an orbiting space vehicle.


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