The trajectory of a dot crossing a pattern of tilted lines is misperceived.

The straight trajectory of a dot crossing a pattern of tilted lines is perceived as being sinusoidal. Manipulation of the size of the angle between the trajectory and the tilted lines, the velocity of the dot, and the distance between the tilted lines shows that the magnitude of the illusion is inversely proportional to the size of the incidence angle, to velocity, and to the distance between the lines. The illusion is interpreted as being the result of an integration process of local distortions occurring at the intersections with the tilted lines.