Demonstration 4 suggested that the anisotropic sensitivity to different motion directions has an effect on the perceived edge displacement, which seems to operate in a similar way to the ‘speed imbalance’ since these two effects can have opposite directions and be subtracted from each other. If the above idea is true, we would also expect that these two effects can be added together in certain circumstance. In this demonstration, we manipulate the ‘speed imbalance’ in the opposite direciton, namely, the speed of the motion signals within the far half-pattern of the contracting pattern was tripled i.e. a ‘speed imbalance (faster far half-pattern of contraction)’ condition. If the above explanation is true, the effect of ‘centripetal bias’ on the perceived edge displacement should have the same direction as that of the ‘speed imbalance’ here. Indeed, we found that our observers perceived an edge displacement with the same direction but stronger than that in Demonstration 2, i.e. now the upper edge (defined by contracting translations) seems more close to the central fixation compared with the lower edge (defined by expanding translations), which suggests that the effect of ‘centripetal bias’ and the ‘speed imbalance’ operate in a similar way and can be added together.