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The Threshold of Rectified Perception as a Clinical TestAuthor(s): Stevenson SmithSource: The Journal of Philosophy, Psychology and Scientific Methods, Vol. 5, No. 8 (Apr. 9,1908), pp. 207-208Published by: Journal of Philosophy, Inc.Stable URL: http://www.jstor.org/stable/2011924 .

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PSYCHOLOGY AND SCIENTIFIC METHODS 207

tional backsets, rather t.han proving that eimotions and passions can be qualitatively distinguished, would seem t.o point to the more natural conclusion that poorly organized affective life has really developed into the more nearly perfected or pure type. This is criticism of a minor point, however, which is in no way intended to reflect upon the high character of the whole treatise. It may serve to call attention to the probable reason why many will not care to accept the particular genealogical structure of Ribot, while in the main agreeing with the author that there is one, and that this possibility offers a most fruitful and interesting field for investiga- tion.

CHARLES HUGHES JOHNSTON. UNIVERSITY OF MICHIGAN.

THE THRESHOLD OF RECTIFIED PERCEPTION AS A CLINICAL TEST

S OME illusions which occur at the beginning of perceptions per- sist more or less constantly as long as the perceptions are

continued or repeated, whereas others disappear after a time when greater familiarity has been had with the stimulus. In the latter cases, where the rectified perception becomes normal, the initial illusion may be wholly lost sight of and only by recourse to the untrained subject may the illusion be determined. Such a tem- porary illusion is the one described here, and the accompanying experimental results indicate a use which may be made of it in clinical tests.

The conditions of the experiment were these: the subject was seated at a table, pencil in hand and paper before him, and was told to observe a chart (see Fig.) which was about to be exposed, and upon its again being screened, to draw what he had seen. The exposure was of two seconds' duration, and the chart was eight feet from the subject's eye. If the subject had perceived the concentric circles as a spiral he was provided with fresh paper and a second exposure made. Thus the exposures were repeated until the subject perceived and drew the circles. The measure of the threshold of rectified perception is the number of exposures. The triangle is introduced into the figure in order to distribute the subject's attention.

Two other tests were made. The first of these was for facility in adding a column of eleven digits. The second was for facility in recalling that letter which, in alphabetical order, comes before each of seven given letters. The letters given were g, p, s, u, i, b, o.

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208 THE JOURNAL OF PHILOSOPHY

These controlled association and adding tests were given to all the subjects of the original experiment. The results are tabulated below,

The figure is two thirds the diameter of the original chart.

together with the combined college grades of the subjects, all of whom were my students, for the preceding two months.

TABLE Exposures in Adding. Association. College grade.

Subject. lst test. sec. sec. Per cent. 1 4 14 60 72 2 8 11 67 83 3 10 13 43 87 4 1 16 18 82 5 3 7 35 89 6 1 20 20 89 7 4 17 85 90 8 1 7 15 91

If the subjects are divided into group one, those who perceived the circles as such at the first exposure, and group two, those who perceived the circles as a spiral, we find no direct correlation between the results of the adding test and the results of the illusion test in the two groups. But the results of the association test show a marked positive correlation with those of the illusion test. The average time in the association test was, for group one, 17.6 seconds, average variation 1.8 seconds; and for group two, 58 seconds, average variation 15.2 seconds. The average college grades are, for group one, 87.3, average variation 3.4; and for group two, 84.2, average variation 5.4.

If a clinical use is made of such an illusion as this to determine the threshold of rectified perception, some better arrangement of the figure may be found, and the conditions should be corrected for abnormal vision. My own subjects all responded normally, showing little variation inter se, to the Snellen alphabet vision tests.

HAMPDEN-SIDNEY COLLEGE. STEVENSON SMITH.

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