Lester E. Krueger Ohio State University
Psychophysical functions relate the subjective magnitude, S, to the physical magnitude, I. They indicate, for example, how loudness increases with auditory intensity. For loudness, like other unidimensional, prothetic modalities, several alternative psychophysical functions are available ( Gescheider , 1988; Marks, 1974a, 1974b; McKenna, 1985; Stevens, 1975). However, Krueger ( 1989) showed that, for a given modality or condition, the four major types of subjective scales--magnitude, partition or category, summated just noticeable difference (jnd), neurelectric--converge "when adjustments are made to remove evident sources of error or bias in the magnitude scale ( Stevens), the category scale is properly corrected, and the summated jnd scale is not constrained by Weber's law ( Fechner). . . . The convergence indicates that sensations are phenomenally experienced [i.e., introspectable via direct magnitude estimation and category ratings] and also are discernible via indirect procedures [summated jnd. neurelectric)" (pp. 251-252). Furthermore, "the convergence of the neurelectric scale with the other three types of scales indicates that there is no additional nonlinear transformation beyond that of the peripheral sensory transducers" (p. 252).
The common subjective scale is approximately a power function,
S = aIb, (1)
in which I is raised to a power or exponent, b, and multiplied by a measure constant, a. The exponent ranges from near 0 to 1 (compressive function;