| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
SACCADIC MOVEMENTS. Sudden movement of the eyes from one fixation point to another.
SAFETY. Freedom from those conditions which can cause injury or death to personnel and damage to or loss of equipment or property.
SATURATION. Extent to which a chromatic color differs from a gray of the same brightness, measured on an arbitrary scale from 0% to 100% (where 0% is gray).
SCINTILLATION. (1) Generic term for rapid variations in apparent position, brightness, or color of a distant luminous object viewed through the atmosphere. (2) A flash of light produced in a phosphor by an ionizing event. (3) On a radar display, a rapid apparent displacement of the target from its mean position. Also called target glint or wander. This includes but is not limited to shift of effective reflection point on the target.
SCOTOMA. A blind or partially blind area in the visual field.
SCOTOPIC ADAPTATION. Like dark adaptation, but with more explicit reference to the part played by the rod system of the retina.
SCOTOPIC VISION. Vision which occurs in faint light, or after dark adaptation. Sometimes called twilight or night vision. Hues and saturations cannot be distinguished.
SCREEN DUMP. Print the contents of a computer display.
SCROLL. Either vertically or horizontally advance through the contents of a computer display.
SEAT REFERENCE POINT (SRP). The point at which the midlines of the seat and backrest intersect.
SECCHI DISK. A white disk which, when submerged to varying depths, aids in determining the color and depth of light penetration in the sea.
SELF-PACED. Experimental or actual task in which a performer's activity is pace solely by the performer.
SENSATION. Subjective response or any experience aroused by stimulation of a sense organ.
SENSING TIME. The time required for a human operator to become aware of a signal.
SENSOR. The nerve endings or sense organs which receive information from the environment, from the organism, or from both.
SENSORY END ORGANS. Receptor organs of the sensory nerves located in the skin or other tissues. Each end organ can sense only a specific type of stimulus. Primary stimuli are heat, cold, or pressure, each requiring different end organs. Knowledge of end organ distribution is of importance to the safety engineer. For example, there are a few heat receptors on the outer surface of the forearm, so that the skin may be severely burned before heat is sensed.
SENSORY FEEDBACK. Signals perceived by sense organs (e.g., eye, ear) to indicate quality or level of performance of an event triggered by voluntary action. On the basis of sensory feedback information, decisions may be made permitting or not permitting an event to run its course; enhancing or decreasing activity levels.
SENSORY NERVE. A nerve (also called afferent nerve) which conducts stimuli from sensory end organs (q.v.) which change physical information (such as pressure, temperature, light) into nerve impulses, to the spinal cord or the brain where cognition occurs and/or the stimulus is converted to a motor signal for transmission via a motor nerve (q.v.)
SEQUENCE-OF-USE PRINCIPLE (EQUIPMENT DESIGN). The principle of arrangement that controls and displays should be so positioned that those used in sequence would be physically arranged in order of operation.
SERVICE TEST MODEL. A model used to determine the characteristics, capabilities, and limitations of a piece of equipment or a complete system under either simulated or actual service operational conditions.
SERVOMECHANISM. A control system which brings a dynamic system to a desired state by operating upon an error signal.
SHADE. Any color darker, i.e., of lower lightness, than median gray.
SHAKE TABLE. A test device for determining the effects of vibration on human or animal subjects or on equipment.
SHAPE CODING. Varying the shape of controls to make them distinctive. Shape coding is effective both visually and actually, that is, the difference can be both seen and felt. The shape of a control should suggest its purpose, and the shape should be distinguishable not only with the naked hand, but also with gloves.
SHORT-TERM MEMORY. The storage of recently received inputs for a period of seconds or minutes.
SHOULDER-ELBOW DISTANCE. From top of acromion to tip of elbow, measured when subject is sitting erect, with upper arm vertical, forearm horizontal.
SIDE TONE. The signal from the talker’s microphone usually returned to the talker via his earphones. This feedback signal is called the side tone. The talker’s speech can be manipulated by varying the side tone.
SIGNAL DETECTION THEORY. A psychophysical model which views human perception as a process in which decisions based on uncertain sensory information are made under conditions of risk.
SIMULATION. A set of test conditions designed to duplicate field operation and usage environments.
SIMULATOR. Any machine or apparatus that simulates a desired condition or set of conditions, such as a flight simulator.
SITTING HEIGHT. The vertical distance from the sitting surface to the top of the head. The subject sits erect, looking straight ahead, with knees at right angles.
SITUATION AWARENESS. The psychological activities involved in attaining a veridical internal representation of the environment.
SI UNITS. Abbreviation of Le Systeme International d’Unites (International System of Units).
SKINFOLD MEASUREMENT FOR ESTIMATING BODY FAT. Permits reasonably close estimation of body fat. Calipers are used to exert a pressure of 10g/mm2 over an area of 20 to 40 mm2,. Measurements are made over the right triceps muscle and below the inferior angle of the right scapula.
SNOW-BLINDNESS. A temporary abnormality of the color sense, in which all objects are tinged with red. Caused by long-continued exposure to very bright light, as in Arctic exploration, on glaciers, in telescopic observation of the sun, watching welding operations, etc.
SOMATOTYPING. A nearly obsolete means of numerical classification of various human body types. Endomorphy: soft, round form with loose, flabby tissue. Mesomorphy: massive, solid form with cubical head, heavy muscles. Ectomorphy: slender limbs and body, with slight head.
SONE. Unit of loudness; a simple tone of 1000 Hz 40 dB above a listener’s threshold produces a loudness of one sone.
SPACE MYOPIA (EMPTY FIELD MYOPIA). A disturbance of the visual accommodative mechanism due to insufficiently sharp detail, making it difficult to detect small objects in the relatively unstructured visual environment of space.
SPECTRUM COLORS. The series of saturated colors normally evoked by photopic stimulation of the retina with radiant energy of continuously differing single wavelengths through the visible range.
SPECULAR REFLECTION. Reflection in which the reflected radiation is not diffused; reflection as from a mirror. Also called regular reflection, simple reflection.
SPEECH ARTICULATION INDEX. The method of estimating the intelligibility of speech by measuring differences (in decibels) between speech and noise levels at different frequency bands.
SPEECH INTERFERENCE LEVEL (SIL). Used as a gross basis for comparing the relative effectiveness of speech in noise. It is usually the simple numerical average of the decibel level of noise in three octave bands, namely, those with centers at 500, 1000, and 2000 Hz.
SPEECH RECOGNITION. An automated process of recognizing spoken language.
SPEECH SYNTHESIS. An automated process of generating spoken language.
SPIN TABLE. A round platform on which human or animal subjects can be placed in various positions and rapidly rotated in order to simulate and study the effects of prolonged tumbling at high rates. Complex types of tumbling can be simulated by mounting the spin table on the arm of a centrifuge.
SQUATTING HEIGHT. The height from the top of the subject’s head to the floor when the subject balances on toes, body erect.
SQUEEZE. Squeeze in diving is due to the effect of increasing external pressure upon the ears and sinuses, the face plate or the swim suit, uncompensated by an equal increase in pressure from within.
STABILIZATION (ZERO G). A condition required during translation and after arrival of a free-floating orbital worker at a desired position inside or outside an orbiting space vehicle. A mechanism is necessary to stabilize the worker against accelerations that may cause visual disorientation, labyrinthine reactions, and movement away from the work area.
STANDARD OBSERVER. A hypothetical observer with a visual response mechanism possessing the colorimetric properties defined by the 1931 ICI tables of the distribution coefficients, x, y, z, and the trichromatic coefficients, x, y, z, of the equal energy spectrum. The y coefficients of the equal energy spectrum are the relative luminosity values defining the standard observer for photometry.
STANDING KNEE HEIGHT. Vertical distance from top of kneecap to floor when subject is standing.
STATIC DISPLAY. A display containing information that does not change.
STATURE. The vertical distance from the floor to the top of the head. The subject stands erect and looks straight ahead.
STEREOSCOPIC ACUITY. Ability to sense three-dimensional aspect of physical space. A function of independent image inputs, i.e., viewing with two eyes. Stereoscopic acuity also depends on brightness contrast and distance from observed objects.
STERNUM HEIGHT. Vertical distance from lower tip of sternum to floor when subject is standing.
STIMULUS. Energy, external or internal, which excites a receptor.
STIMULUS GENERALIZATION. An aspect of learning characterized by the spreading of a response learned in association with one stimulus to other stimuli which are similar but not identical to the first.
STPD CONDITIONS. Standard temperature and pressure, dry. These are conditions of a volume of gas at 0°C, at 760 torr (101.32472kPa) without water vapor. A STPD volume of a given gas contains a known number of moles of that gas. (See BTPS CONDITIONS.)
STRESS. (1) The force per unit area on a body that tends to produce a deformation. (2) The effect of a physiological, psychological, or mental load on a biological organism which may produce fatigue and degrade proficiency.
STROBOSCOPE. An optical instrument for observing moving bodies by making them visible intermittently. If the motion is cyclic, such as rotation or vibration, an optical illusion is created of the moving body being stationary or moving at a slower rate. (See FLICKER FUSION.)
STROPHOSPHERES. Defines the region in a person’s fixed workplace that is common to the hand motions made with various hand manipulations.
SUBJECT. A member of a specified population from whom an experimenter obtains response data for specific stimulus variables. The data obtained are often generalized to that population.
SUBJECTIVE EXPECTED UTILITY (SEU). A decision making model which assumes a decision maker will enumerate the set of feasible alternatives and select the alternative that maximizes expected utility.
SUPERVISORY CONTROL. A mode of control in which a human operator or team monitors and manages the operation of automated or semi-automated systems which control a system.
SURROUND BRIGHTNESS. The brightness of the area immediately adjacent to an area of visual work.
SYSTEM. A composite of equipment, skills, and techniques (including all related facilities, equipment, material, services, and personnel) that is capable of performing and/or supporting an operational role.
SYSTEM ANALYSIS. Identification of the dynamic relationships between elements of a system.
SYSTEM ENGINEERING. The study and planning of a system so that the relationships of various parts of the system are fully established before designs are committed, or to look for improvements in existing systems.
< Previous | Next >