The influence of sensory reflexes in the eye upon the process of visual orientation was next taken up in connection with two specific types of stimulation. At top and bottom of the vertical screen were arranged dark lanterns consisting of electric bulbs enclosed in blackened boxes, the fronts of which were covered with a series of sheets of white tissue-paper, by which the light was decentralized and reduced in intensity, and of blue glass, by which the yellow quality of the light was neutralized. Either of these lanterns could be illuminated at will by the pressure of a button. All other experimental conditions remained unchanged. The observers were directed to pay no special regard to these lights, and the reports show that in almost every case they had no conscious relation to the judgment. The results are presented in the following table:
Below. Light Above.
Observer. Const.Err. Av.Dev. M.Var. Const.Err. Av.Dev. M.Var.
C (40) +156.37 156.37 19.67 +169.85 169.85 19.22
D (20) + 39.30 43.30 17.95 + 46.65 47.35 15.41
F (30) + 19.47 19.47 8.83 + 58.37 58.37 7.83
G (50) + 66.11 112.76 14.65 +117.86 117.86 13.10
H (30) -147.63 147.63 21.07 -105.30 105.30 30.31
J (20) + 1.90 31.95 22.33 + 44.40 44.40 20.55
Average: + 22.59 85.28 17.42 + 55.30 90.52 17.74
The eye is uniformly attracted toward the light and the location of the disk correspondingly elevated or depressed. The amount of displacement which appears is relatively large. It will be found to vary with the intensity, extent and distance of the illuminated surfaces introduced. There can be little doubt that the practical judgments of life are likewise affected by the distribution of light intensities, and possibly also of significant objects, above and below the horizon belt. Every brilliant object attracts the eye toward itself; and the horizon beneath a low sun or moon will be found to be located higher than in a clouded sky. The upper half of the ordinary field of view—the clear sky—is undiversified and unimportant; the lower half is full of objects and has significance. We should probably be right in attributing to these characteristic differences a share in the production of the negative error of judgment which appears in judgments made in daylight. The introduction of such supplementary stimuli appears to have little effect upon the regularity of the series of judgments, the values of the mean variations being relatively low: 17’.42 with light below, 17’.74 with it above.