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FIG. 3. (a) The relation between the size of the test-object and the threshold

brightness. (b) The relation between contrast and brightness for the 3 and 2 mm test-objects.

High contrast is indicated by the dots, low contrast by the circles. In each family of four curves, the times of exposure are ad libitum, 200, 100, and 500, respectively, from left to right. A and B, ten and twenty-one subjects respectively as before.

s. RECIPROCAL OF TIME

the result of changing to the low contrast has been to make necessary nearly a fourfold increase in the exposure time. Ab and Bb of Fig. 3 show the relation between contrast and brightness, for the 3 mm. and the 2 mm. test-objects, which are the only ones comparable in this way. The increment of log. brightness necessary to offset the lowered contrast is seen to be larger the smaller the test-object and the shorter the time of exposure.

It remains to draw a comparison between these results and those of an earlier communication (2). Of the latter, there is one set which is comparable to certain of the present sets. Four subjects participated, only one of whom is included in the group here concerned. The test-object was of the same design, but the unit-dimension was 3.18 mm. (inch) instead of 3 mm. exactly, and it was preceded and followed by similar

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FIG. 4. The results for the 3 mm., high contrast test-object (A, B) compared with previous results (II.) obtained with a 3.18 mm. ( inch test-object of like design). Curve II. embodies the same results as Curve II., 4, Fig. 11, this Journal, 1925, 8, 95.

confusion-patterns. These earlier results are plotted in Fig. 4, to the same coördinate scales as are used in Fig. 1, and on the same plot are reproduced the curves from Fig. 1, A and B (3 mm. test object, high contrast) for 10 and for 21 subjects respectively. The latter, as will be seen, meets the curve from the earlier work, while the former parallels it at a somewhat lower brightness.

It is to be remembered that aside from representing different groups of subjects the results intercompared were taken by different methods. In the earlier experiments fixed levels of brightness were used and the exposure-time was the experimental variable actually measured; while the reverse was the procedure for the present work. Furthermore, in the present work fixation was directly upon the test-object, while in the earlier the test-object was 2° to the right of the fixationpoint. The comparison shown in Fig. 4 nevertheless would seem to indicate that the essential differences between the two sets of results are by no means radical.

SUMMARY

1. The work described in this paper is a continuation of earlier experiments, in which the relations between the brightness of a visual object and its time of exposure are investigated as they exist at the threshold. As before, a simple test object is used, preceded and followed at the same point in the visual field by confusion-patterns.

2. This work differs from the earlier work in several essential ways:

(a) Larger groups of subjects were employed, each one being engaged for a much shorter time. As a rule, therefore, these individuals were less experienced with the experimental technique than before.

(b) For this reason they were instructed to fixate the testobject directly, instead of fixating an auxiliary mark 2° to the left of the test-object, as before.

(c) Conditions involving longer times of exposure were investigated. This made it advisable to use fixed times of exposure, and to make brightness the immediate experimental variable. In the interests of expediency, certain modifications in the apparatus were incidentally made.

(d) In addition to the white and black test-objects formerly used, a new group of test-objects was introduced having a lower contrast between the figure and the ground upon which the figure appeard.

3. In general, the effect of changing from the higher to the lower contrast (from 100 : 4 to 100: 73) was about equal to the effect of reducing the size of the high contrast (100 : 4) test-object one step in the size-series: 3, 2, 1 mm. Thus the test-object, disregarding for the moment the factor of time, could be made more difficult in either of two ways.

4. For any given test-object it was found that the "speed" (reciprocal of the threshold-time of exposure) increased approximately in proportion to the logarithm of the brightness; the exception being that, if anything, at higher speeds (time reduced from 100 to 50°), the same increment in speed was accomplished with a somewhat less than proportionate increase in brightness. This was perhaps more strictly true of the more difficult test-objects, the times of exposure varying from ad libitum to 500.

5. Increasing the difficulty of the test-object by reducing either its contrast or its dimensions had the effect that the identical increase in speed was accomplished only with the help of a relatively larger increase in brightness. That is to say that the general slope of the curve, plotted as in Fig. 2, became less.

REFERENCES AND COMMENTS

1. This JOURNAL, 1923, 6, 138–160.

2. This JOURNAL, 1925, 8, 77–108.

3. This material was furnished by the courtesy of the E. I. du Pont de Nemours and Company. Its trade-name is 'Pyralin.'

4. The distances 1, 2, 3 and 4 mm, as seen from 6 meters, subtend respectively 0.86, 1.15, 1.72 and 2.58 minutes' angle at the subject's eyes.

5. This fact may appear to stand in contradiction to certain conclusions that have been stated elsewhere; e.g., Luckiesh, Light and Work, (Van Nostrand, New York, 1924) p. 191; Ferree and Rand, Tran. Illum. Eng. Soc., 1922, 17, 76. These conclusions are to the effect that a relatively greater increase in speed of vision arises from the same increase in light when a more difficult test-object (smaller or of lower contrast) is in question. It will be evident, however, that these statements refer to an identical increase in illumination with different initial speeds; while the statement in the text above refers to identical changes in speed which take place within widely separated ranges of brightness. No contradiction whatever is involved, as will be seen from a study of Fig. I with this distinction in mind.

THE ABILITY OF CHINESE STUDENTS TO READ·

IN VERTICAL AND HORIZONTAL

DIRECTIONS 1

BY L. K. CHEN AND H. A. CARR

University of Chicago

This experiment is concerned with the relative facility with which Chinese students apprehend reading materials arranged in vertical and horizontal columns. The experiment made use of the reading of textual materials and the cancellation of certain characters.

The reading materials consisted of two passages of Chinese prose (in Chinese characters) of approximately the same length and degree of difficulty. Each of these passages was mimeographed in vertical and horizontal columns. The subjects were requested to read a passage through twice, as quickly and as carefully as possible. The time required for this task was recorded in seconds. The subjects were then requested to give an oral reproduction of the material. Each passage was divided into eighty-three logical items, and each subject was scored on the basis of the number of these items correctly reported. Each subject was tested for one passage with the vertical arrangement and the other passage with the horizontal arrangement. Four groups of subjects were employed, and the order of testing the groups was so arranged as to compensate for practice and any difference in the difficulty of the two materials.

The materials for cancellation included Chinese characters, English letters and Arabic numerals. Each material was mimeographed with the two arrangements, but the subjects were required to cancel different characters in the two cases. The order of testing the four groups was so arranged as to eliminate the effects of practice and any differences of difficulty. For each material, the subjects were requested to 1 From the Psychological Laboratory of the University of Chicago.

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