Figure 1.

Depiction of flow parsing process whereby the component of optic flow due to the observer's self-motion on a straight-forward heading (middle) is subtracted from combined optic flow (self-motion + object motion; top). Red arrow indicates the object's motion independent of self-motion. Gray arrow indicates motion of background element at same location due to self-motion. Blue array indicates combined motion. Top, The object motion component and self-motion component sum to determine the object's retinal motion, which is directly upwards in this scenario. After the self-motion component is factored out, the resultant flow (bottom) reflects object motion in a world-fixed reference frame.