Anomalous contours

In Circle without gradient collinear line terminators generate curvilinear anomalous contours, which border an apparently brighter stripe. In Margin without gradient line terminators generate an anomalous contour that separates two regions where conditions for brightness contrast are identical. Anomalous contours are locally perpendicular to inducing lines; but when these are distributed on both sides of the anomalous contour (like in Margin without gradient) the depth stratification is ambiguous and the brightness differentiation is lacking. Nervatures in Trunk, 1982, are bordered by anomalous contours perpendicular to the local directionality of brushstrokes. In Trunk, 1972, (on the table) the segregation of homogeneous textures (produced by uniform micro-brushstrokes) is sometimes reinforced and sometimes contrasted by the line scribble, with a consequent perceptual instability.