Z94.9 Human Factors (Ergonomics) Engineering

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VALIDITY (TEST). The degree to which a test measures what it was designed to measure, estimated by means of coefficient of correlation between test scores and a criterion measure, such as actual on-the-job performance; empirical validity.

VALUE. (1) The dimension of the Munsell system of color which corresponds most closely to lightness. (2) Numerical quantity. (3) Worth, as in value engineering.

VARIED MAPPING. A variable relationship between stimuli and desired response.

VERBAL MEDIATION. The technique of verbalizing instructions or directions so as to emphasize cue-response relationships in learning or performing a task; used especially during the early stages of learning.

VERBAL PROTOCOL ANALYSIS. A method of behavioral measurement involving the collection and examination of the verbal behavior of a performer.

VERTIGO. Sensation of dizziness or whirling, in which objects, though stationary, appear to move in various directions, and the person finds it difficult to maintain an erect posture. It may result from overstimulation of the sense organs, from changes in the blood supply of the brain, or from disease. “Aviator’s vertigo,” caused by conflict between visual and gravitational cues, results in a disturbance in the pilot’s orientation with respect to the earth.

VIEWING ANGLE. The angle formed by a line from the eye to the viewed surface.

VIGILANCE. An activity or type of research involving continuous watch and the ability of individuals to detect signals of varying frequencies during these watches.

VISUAL ACUITY. The ability to recognize objects or sets of objects by eye as distinct, specific and separate. Depends on illumination, object size, distance from object to observer, object configuration and brightness of contrast. Expressed quantitatively as the ratio of distance at which the observer recognizes to the distance at which a normal eye recognizes. 20/100 indicates that a person recognizes at 20 feet a sight chart which can be seen by the normal eye at 100 feet. Visual acuity of individuals should be matched to the needs of their task assignments.

VISUAL FIELD DEFECT. A condition of impaired eyesight where the eye cannot see portions of the area in its field of vision. Blind spots of various size and position exist. Visual field defects are sufficiently common to warrant consideration in work placement. Not usually detected in eye examination for visual acuity (q.v.).. Should be suspected whenever a person appears to be accident-prone.

VIRTUAL ENVIRONMENT. Artificial, typically computer generated, stimulation of the senses to give the subjective impression of existence within a particular environment.

VIRTUAL IMAGE. An image that cannot be shown on a surface but is visible, as in a mirror.

VISIBILITY. The capacity of radiant energy, within a certain range of wavelengths, to excite a visual receptor process and thereby evoke the phenomenon of brightness.

VISION, FOVEAL. Visual sensations or perceptions due to stimulation of the fovea centralis, or center of the retina.

VISION, PERIPHERAL. Visual sensations or perceptions due to stimulation of the outlying portions of the retina.

VISION, PERSISTENCE OF. The tendency of visual excitation to outlast the stimulus, or more generally the tendency of changes in visual sensory response to lag behind changes in the stimulus.

VISUAL ACUITY. The ability to perceive detail at various distances. More specifically, it can be expressed as the reciprocal of the visual angle, in minutes of arc, that is subtended by the smallest detail that can be visually discriminated.

VISUAL ANGLE. The angle subtended by an object in the visual field at the nodal point of the eye. The angle determines the size of the image on the retina. Objects of different sizes or distances have the same-sized image on the retina if they subtend the same angle.

VISUAL ADAPTATION. Adjustive change in visual sensitivity due to continued visual stimulation. Three recognized types are: (1) scotopic or dark adaptation, (2) photopic or light adaptation, and (3) chromatic or color adaptation.

VISUAL FIELD. That part of space that can be seen when head and eyes are motionless, (or) the totality of visual stimuli which act upon the unmoving eye at a given moment.

VISUAL PHOTOMETRY. A subjective approach to photometry, wherein the human eye is used as the sensing element; to be distinguished from photoelectric photometry.

VISUAL RANGE. The distance, under daylight conditions, at which the apparent contrast between a specified type of target and its background becomes just equal to the threshold contrast of an observer; to be distinguished from the night visual range. Also called daytime visual range.

VISUAL SPACE. This term, like visual field, refers to the extended world as perceived by means of the eyes but is commonly used in a more generic and abstract way in discussions of the perception of distance and length, of depth or distance away from the retina, and of form or figure in two and three dimensions.

VOLUME (TONAL). Volume is that attribute of auditory sensation in terms of which sounds may be ordered on a scale extending from spatially small to spatially large.

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