Rogers Brian, Rogers Cassandra
Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OX1 3UD, UK.
Perception. 2009;38(9):1295-312. doi: 10.1068/p6328.
Helmholtz's famous distorted chessboard pattern has been used to make the point that perception of the straightness of peripherally viewed lines is not always veridical. Helmholtz showed that the curved lines of his chessboard pattern appear to be straight when viewed from a critical distance and he argued that, at this distance, the contours stimulated particular 'direction circles' in the field of fixation. We measured the magnitude of the distortion of peripherally viewed contours, and found that the straightness of elongated contours is indeed misperceived in the direction reported by Helmholtz, but that the magnitude of the effect varies with viewing conditions. On the basis of theoretical considerations, we conclude that there cannot, in principle, be particular retinal loci ('loci' is used here in the sense of an arc or an extended set of points that provide a basis for judging collinearity) to underpin our judgments of the straightness and parallelity of peripheral contours, because such judgments also require information about the 3-D surface upon which the contours are located. Moreover, we show experimentally that the contours in the real world that are judged to be straight and parallel can stimulate quite different retinal loci, depending on the shape of the 3-D surface upon which they are drawn.
亥姆霍兹著名的变形棋盘图案曾被用来证明，对周边视野中线条直线度的感知并不总是准确的。亥姆霍兹表明，当从某个特定距离观察时，他的棋盘图案中的曲线看起来是直的，并且他认为，在这个距离上，这些轮廓刺激了注视区域中特定的“方向圆”。我们测量了周边视野中轮廓的变形程度，发现细长轮廓的直线度确实如亥姆霍兹所报告的方向那样被误判了，但这种效应的程度会因观察条件而异。基于理论考量，我们得出结论，原则上不可能存在特定的视网膜位点（这里的“位点”是指一段弧线或一组扩展的点，为判断共线性提供基础）来支撑我们对周边轮廓直线度和平行度的判断，因为这种判断还需要有关轮廓所在三维表面的信息。此外，我们通过实验表明，在现实世界中被判断为直且平行的轮廓，会根据其绘制所在三维表面的形状，刺激截然不同的视网膜位点。
