2008 年 79 巻 2 号 p. 125-133
We investgated visual illusions of a vertical gradient by using minitures of a road in three experiments. The independent variables were the pitched visual pattern around the road and the pitched floor on which the observer stood. The dependent variable was the angle of the road that the observer adjusted to appear to be level in depth. In Experiment 1, the experimental room was pitched independently of the pitched floor on which the observer stood. Pitching the room was found to be effective for the illusion, but pitching the floor was not. In Experiment 2, the horizontally striped pattern of the sidewalls was pitched in the range of ± 30° and the height of the sidewalls was also varied. The illusion was found to be maximal for patterns pitched at ± 10°, but the sidewall height did not influence the illusion. In Experiment 3, six visual patterns that were produced by combining horizontal and vertical stripes were pitched at ± 10°. The results showed that the lattice pattern was the most effective, and the horizontal stripe was more effective than the vertical, in contributing to the illusion.