Asymmetries in texture perception.

Single elements in textures segregate preattentively from the background if they differ in special features from surrounding elements (pop-out). Oblique targets on a background of vertical line elements are more easily detected than vertical targets on a ground of oblique elements. We wanted to find out whether this perceptional asymmetry depends on the absolute orientation or on the alignment of the background lines. Using the method of constant stimuli, we measured the thresholds of detection times in five subjects using four different arrangements of line patterns. The subjects indicated the position of a salient element in a forced-choice procedure. For all subjects, detection times were shortest if background lines were either vertical or collinear. Otherwise, detection times were significantly longer by a factor of 3. Figure-ground segregation is facilitated if background lines are either vertical or collinear.