Myers, C. S. (1911). On the psycho-physical methods. In C. S. Myers, A text-book of experimental psychology with laboratory exercises, Part-1: Text-book (pp. 189-204). New York, NY, US: Cambridge University Press.
http://dx.doi.org/10.1037/13781-015
This chapter examines the uses of psycho-physical methods. Methods Usage—The principal object of these methods is to determine the conditions of our experiences of equality and difference. This forms a most important theme of research in experimental psychology. [For experiences of equality and difference underlie (i) the determination of the 'differential threshold,' in which the smallest appreciable difference, produced by two different stimuli, is ascertained. The same experiences are in great measure involved in (ii) the determination of the 'absolute threshold' of an experience (the presentation, for example, being one of minimal intensity or quality, or one of minimal temporal or spatial extent); for here, as we shall subsequently see, the subject's attitude is one of more or less conscious discrimination between the just appreciable and the inappreciable. Experiences of equality and difference are also involved in determining the conditions of apparent equality between two experiences. Apparent equality may relate simply to (iii) the experiences of two objects; as, for example, in the determination of equality in the lengths of two lines or in the brightness of two lights. On the other hand, it may relate to (iv) the experience of the differences between two pairs of objects; as, for instance, when we determine that the difference between the loudnesses a and b of one pair of sounds is equal to the difference between the loudnesses of b and c (or c and d) of another pair of sounds. In none of these four lines of research can we strictly be said to measure subjective experiences of equality or difference. We can only measure the objective intensities (or extents) of stimuli which produce those experiences. Hence, speaking in terms of physical stimuli, in place of psychic experience, we may say that these four lines of research respectively involve the determination of (i) the differential threshold of the stimulus, (ii) the absolute threshold of the stimulus, (iii) the apparent equality of stimuli, and (iv) the apparent equality of stimulus differences. For the investigation of these four problems three so-called 'psycho-physical' methods have been devised, intimate familiarity with which is essential for reliable experiment. They are 'the method of mean error,' 'the limiting method,' and 'the constant method.'] (PsycINFO Database Record (c) 2016 APA, all rights reserved)