Fig. 3: Combination of observer and object motion and the resulting flow components used for the simulations.

Black points indicate the static points of the scene, and green ones illustrate five cases of independently moving objects. Objects, for clarity represented by only one point each, are placed at five of the 49 retinal positions used in the study, each serving as an example for one of the five object motion conditions. The paradigm simulated to validate the model always actually contained only one object per scene, which consisted of multiple dots (see Fig. 9 for the detailed description). a shows the observer flow (black lines), which occurs when only the observer moves. Observer movement is a translation towards the center of the panel, resulting in a radial pattern encompassing all points in the scene. b shows the isolated flow of the objects. Object movement in the world consists of two components: the horizontal movement resulting in horizontal flow (red, dotted lines) and the component based on motion in depth, both the observer’s (translation T) and the object’s, which is varied in the different conditions (dotted lines, colors corresponding to conditions specified in (d)). The flow resulting from the object’s motion in depth is a multiple of the observer flow as the object moves in the direction λ ⋅ T in the world. The object flow (green lines) is the sum of the flow due to the horizontal and the in-depth movement (dotted lines). c shows the combined flow (white lines), which is sum of observer and object flow. d shows two flow metrics resulting from adding object movement into a previously static scene. This addition changes the flow in speed and direction of all points related to the moving object. Speed ratio indicates the rate of average velocities of combined flow to observer flow, with values above 1 signaling an increase in flow velocity. Direction deviation is the average, unsigned angle between the combined and observer flow vectors.