Figure 1.

Uniform motion in the environment can produce nonuniform visual motion information. We input different patterns to a simple motion energy algorithm following (Adelson and Bergen, 1985). a, A pattern of circles, containing equal image information at all orientations, is moved by equal amounts along cardinal (blue) or oblique (orange) directions. Motion energy filters detect visual motion information at circle edges perpendicular to the direction of motion (gray squares with filter energy shown in orange and blue for one example oblique and cardinal direction, respectively). The amount of total motion energy produced by the patterns is the same in any motion direction (polar plot). b, A pattern of ellipses, which, like natural images, has more edges at cardinal orientations, produces stronger motion energy when moved in cardinal directions.