The inclined position of the screen was of course observed by every reactor, but of the changes in the enclosing walls no subject was informed, and none discerned them on any occasion. Each observer was questioned as to alterations in the experimental conditions after the use of each arrangement, and at the close of the whole series inquiry was made of each as to the planes of the upper boundaries of the walls. On various occasions, but not customarily, the observer was aware of a change of some kind in the whole set of conditions, but the particular feature altered was not suspected. The results for all three arrangements are given in the following table; of the sections of this table the third is incomplete, full results having been reached in the cases of only three observers:
Ascending Planes. Descending Planes. Observer Const. Err. Av. Dev. M. Var. Const. Err. Av. Dev. M. V. C (50) — 8.02 11.82 9.47 — 48.14 48.14 9.52 F (50) + 78.88 78.88 2.89 + 25.54 25.54 1.98 G (50) — 22.56 24.64 6.58 -101.20 101.20 7.39 H (50) — 83.84 83.84 11.78 -230.20 230.20 11.88 J (50) +315.64 315.64 18.16 +120.12 120.12 9.01 Average: + 55.96 102.96 9.78 -44.98 104.84 7.96
Horizontal Planes. Observer. Const. Err. Av. Dev. Mean Var. C (50) — 27.86 27.86 9.58 G (50) — 73.84 73.84 7.59 J (50) +243.72 243.72 18.52
For every individual observer, the position of the disc on the screen has been affected by each change in the direction of these visible lines. In every case, also, its location when these boundaries lay in a horizontal plane was intermediate between the other two. The importance of such relations in the objects of the visual field as factors in our ordinary determination of the subjective horizon is made evident by these experimental results. They become construction lines having assumed permanence in the world of visual-motor experience. The conception of unchanging spatial relations in the fundamental lines of perspective vision receives constant reinforcement from the facts of daily experience. The influence of the above-described changes in experimental conditions is mediated through their effect upon the location of the focus of the limiting and perspective lines of vision. As the plane of the upper boundaries of the enclosing walls was elevated and depressed the intersection of the two systems of lines was correspondingly raised and lowered, and in dependence upon the location of this imaginary point the determination of the position of the white disc was made, and the plane of perspective positively or negatively rotated.