Asymmetric spatial distributions of motion vectors yield characteristic errors in direction judgements

For a continuous flow field depicting a combined translation and expansion, there exists a natural distribution of local motion directions whose mean direction corresponds to the direction of translation. A random sampling of this distribution may introduce spatial asymmetries and thus alter the mean direction. This statistical phenomenon has a perceptual parallel: the spatial distribution of the dots becomes relevant with respect to the perceived global direction. The perceived direction of motion corresponds to the mean direction, not to the actual direction of translation.