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a psychological discipline that studies the quantitative relations between the physical characteristics of a stimulus and the intensity of the sensation evoked by the stimulus.
Psychophysics deals with two main groups of problems: measurement of the stimulus threshold, that is, the sensitivity limit of the human sensory system, and the construction of psychophysical scales. The first group of problems arose as a result of measurements of the intensity of sensation made in the 19th century by the German scientists W. E. Weber and G. Fechner; these measurements involved indirect scaling, in which the intensity of sensation is a mathematical function of the magnitude of the stimulus. The threshold was regarded as the point in a series of stimuli of increasing intensity that divides the series into two parts, one that causes sensation and one that does not. Modern psychophysics—or rather its applied branch, the theory of detecting signals against a background of noise—regards the threshold as a “threshold zone,” within which the probability of a response varies between 0 and 1. Dynamic sensitivity theories deny that a sensory threshold exists as an independent reality.
The second group of problems arose in connection with the use by the American scientist S. Stevens of direct scaling. In direct scaling, the magnitude of sensation—a point on the sensory scale—is determined by the subject’s own indication of the distance or relation between the intensities of stimuli in arbitrary units. Research on both groups of problems is concerned with the main theoretical problem of psychophysics, namely, the structure and metrics of the psychophysical stimulus space of sensations, which is understood as a multivector, noneuclidean space.
REFERENCESKravkov, S. V. Ocherk obshchei psikhofiziologii organov chuvstv. Moscow-Leningrad, 1946.
Eksperimental’naia psikhologiia, fascs. 1–2. Edited by P. Fraisse and J. Piaget. Moscow, 1966. (Translated from French.)
Problemy psikhofiziki: Sb. Moscow, 1974.
Fechner, G. T. Elemente der Psychophysik, 3rd ed., vols. 1–2. Leipzig, 1907.
Guilford, J. P. Psychometric Methods, 2nd ed. New York, 1954.
V. I. MAKSIMENKO