Figure-ground discrimination by the visual system of the fly

A small black object embedded in a black-white contrasted random-dot texture, is easily confused by a human observer with the ground. However, even small relative motions between object and ground allow an easy detection. A similar observation is made when the object is replaced by a figure consisting of the same random-dot texture as the ground. As long as the figure is not moved against the ground, figure-ground discrimination is not possible as the boundary of the figure disappears in the texture of the ground. However, when the figure is moved relative to the ground, the boundary of the figure can be easily seen. In some sense relative motion between figure and ground leads to an independent or context free perception of a figure. The observations are of course different when the texture of the figure differs from the texture of the ground. Under these conditions one can usually see the figure’s boundary and its content even if it is not moved relative to the ground