Comparison of empirical predictions and psychophysical results for moving lines seen in a vertical slit aperture. A) The aperture. B) Distributions of the projected directions of moving lines in different orientations constrained by a vertical slit. The green arrows are results of psychophysical testing; the red arrows are the empirical predictions; the gray arrows indicate vertical. The predictions are again in good agreement with psychophysical results. (After Sung et al., 2008)