The time of perception as a measure of differences in sensations / by Vivian Allen Charles Henmon.
- Henmon, Vivian Allen Charles (V. A. C.), 1877-
- Date:
- 1906
Licence: In copyright
Credit: The time of perception as a measure of differences in sensations / by Vivian Allen Charles Henmon. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
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![In addition to the difficulties involved in the unit of measurement, there are likewise methodological difficulties in determining it. The psychophysical methods, according to the classification of Wundt, fall into two classes, the gradation methods and the error methods. The gradation methods are the method of just noticeable difference (method of least differences [Muller], method of minimal changes. [Wundt]) and the method of mean gradations. The error methods- are the method of right and wrong cases and the method of average error. It is not our purpose to give a statement of the principles and methods of procedure in the use of these methods. This is given in the text-books on psychology. It is proposed to merely note the objections urged against them as means of measuring differences in sensations. The method of just noticeable difference, in the old form in which it was used by Weber and Fechner, which consisted of adjusting a difference after various trials until it seemed just noticeable, was soon found to be unsystematic and unsatisfactory. Refinements in the mode of procedure in the application of the method were made by Muller (method of least differences), by Wundt (method of minimal changes) and by Jastrow (method of gradual increments). In spite of these improvements many investigators have found much to criticize in the method. Jastrow points out in connection with Weber’s experiments the ambiguity of the term just noticeable. He saysd “This expression may have as many as four practically distinct meanings. It may refer to (1) two pressures sufficiently different to enable the subject sometimes to tell which is which; or (2) to differences that will always be correctly recognized; or (3) such as will only ac- cidentally fail to be recognized; or finally (4) it may refer to differences which will be correctly judged any characteristic proportion of the times between these extremes.” With any of these meanings, the difference fixed upon will vary with individuals and at different times. As Fullerton and Cattell, who found the method unsatisfactory, state it:^ “The clearness with which a difference is distinguished varies gradually from complete doubt to complete certainty. The variation is continuous and no point can be taken and called the ‘ just noticeable difference ’ and kept constant for different observers and for the same observer at different times. If complete certainty be taken as the standard a difference in the stimuli will be required much greater than that which can ordinarily be distinguished and the standard will be found to differ greatly with different observers, measuring, if anything, rather their character than their fineness of sensation ” The influence of ex- * Joseph Jastrow, ‘Psychophysical Methods,’ Am. Jour, of Psychol.^ i: 274, 1888. ’ Fullerton and Cattell, On the Perception of Small Differences,-^, ri, 1892.](https://iiif.wellcomecollection.org/image/b24917059_0009.jp2/full/800%2C/0/default.jpg)
