Oblique effect

Oblique effect is the name given to the relative deficiency in perceptual performance for oblique contours as compared to the performance for horizontal or vertical contours. Oblique effect is the name given to the relative deficiency in perceptual performance for oblique contours as compared to the performance for horizontal or vertical contours. The earliest known observation of this effect came about in 1861 when Ernst Mach completed an experiment in which he set a line to make it appear parallel to an adjoining one, and found observers' errors to be least for horizontal and vertical orientations and largest for an inclination of 45 degrees. The effect can be demonstrated for many visual tasks and was named oblique effect in the widely cited article by Stuart Appelle.