Comparison of empirical predictions and psychophysical results for moving lines seen in a circular aperture. A) The circular aperture. As in Figure 8, line orientation (q) is measured from the horizontal axis; the direction of movement is measured as positive and negative deviations from the perpendicular direction (indicated as 0º) with respect to the line orientation. B) The distributions of the projected directions constrained by circular aperture. The green arrows indicate the directions reported in psychophysical testing; the red arrows indicate the directions predicted by empirical analysis. The directions of the red and green arrows are nearly the same. Inset shows the method of psychophysical testing; subjects were asked to indicate the perceived direction by adjusting the green arrow to correspond to the direction elicited by the lines moving in the aperture. (After Sung et al., 2008)