Plaid stimuli are formed by two superimposed gratings consisting of parallel lines that both move in normal flow direction. The stimuli are presented in a circular aperture. A) In plaids of type I the direction of the gratings lie on either side of the generated pattern motion. In this case, the vector average of the two motion vectors and the intersections of constraints (IOC) rule will result in (approximately) the same direction. This stimulus was typically used when investigating the pattern response in area MT. B) Plaids of type II are characterized by gratings moving in similar direction, i.e. both lying on the same side with regard to the movement that is generated at the 2D crossings. In this case, vector average and the IOC rule will lead to different directions. For this reason, this stimulus provides the possibility to distinguish the computation rule used. Note that a feature signal will lead to the same results as the IOC rule.