van Ee R, Banks M S, Backus B T
School of Optometry and Vision Science Program, University of California at Berkeley 94720-2020, USA.
Perception. 1999;28(9):1121-45. doi: 10.1068/p281121.
When a small frontoparallel surface (a test strip) is surrounded by a larger slanted surface (an inducer), the test strip is perceived as slanted in the direction opposite to the inducer. This has been called the depth-contrast effect, but we call it the slant-contrast effect. In nearly all demonstrations of this effect, the inducer's slant is specified by stereoscopic signals; and other signals, such as the texture gradient, specify that it is frontoparallel. We present a theory of slant estimation that determines surface slant via linear combination of various slant estimators; the weight of each estimator is proportional to its reliability. The theory explains slant contrast because the absolute slant of the inducer and the relative slant between test strip and inducer are both estimated with greater reliability than the absolute slant of the test strip. The theory predicts that slant contrast will be eliminated if the signals specifying the inducer's slant are consistent with one another. It also predicts reversed slant contrast if the inducer's slant is specified by nonstereoscopic signals rather than by stereo signals. These predictions were tested and confirmed in three experiments. The first showed that slant contrast is greatly reduced when the stereo-specified and nonstereo-specified slants of the inducer are made consistent with one another. The second showed that slant contrast is eliminated altogether when the stimulus consists of real planes rather than images on a display screen. The third showed that slant contrast is reversed when the nonstereo-specified slant of the inducer varies and the stereo-specified slant is zero. We conclude that slant contrast is a byproduct of the visual system's reconciliation of conflicting information while it attempts to determine surface slant.
当一个小的正前方平行表面（测试条）被一个更大的倾斜表面（诱导物）包围时，测试条会被感知为朝着与诱导物相反的方向倾斜。这一现象过去被称为深度对比效应，但我们称之为倾斜对比效应。在几乎所有关于此效应的演示中，诱导物的倾斜是由立体视觉信号确定的；而其他信号，如纹理梯度，则表明它是正前方平行的。我们提出了一种倾斜估计理论，该理论通过各种倾斜估计器的线性组合来确定表面倾斜度；每个估计器的权重与其可靠性成正比。该理论解释了倾斜对比现象，因为诱导物的绝对倾斜度以及测试条与诱导物之间的相对倾斜度，两者的估计可靠性都高于测试条的绝对倾斜度。该理论预测，如果确定诱导物倾斜度的信号相互一致，倾斜对比将被消除。它还预测，如果诱导物的倾斜度是由非立体视觉信号而非立体视觉信号确定的，将会出现相反的倾斜对比。这些预测在三个实验中得到了检验和证实。第一个实验表明，当诱导物的立体视觉指定倾斜度和非立体视觉指定倾斜度相互一致时，倾斜对比会大大降低。第二个实验表明，当刺激由真实平面而非显示屏上的图像组成时，倾斜对比会完全消除。第三个实验表明，当诱导物的非立体视觉指定倾斜度发生变化而立体视觉指定倾斜度为零时，倾斜对比会反转。我们得出结论，倾斜对比是视觉系统在试图确定表面倾斜度时对冲突信息进行协调的副产品。
