Figure 3: The direction index of the responses of the model is plotted as a function of stimulus displacement. Circles represent the response of the first-order channel, squares the second-order. The layout of the figure corresponds to that of Figure 1. The Gabor micropatterns have a carrier wavelength, l, of 8 pixels. The mean centre-to-centre spacing of the micropatterns is 40 pixels (5l) in the sparse condition and 20 pixels (2. 5l) in the dense. A direction index of +1 corresponds to motion unambiguously in the correct direction, -1 to motion in the opposite direction, and 0 to no motion or equal and opposite motions. Details of the calculation of the direction index are given in the Appendix.