Figure 5.

STAF validation: reverse-phi illusory motion. For a periodic stimulus, reversing the contrast polarity of the pattern during apparent motion generates the illusion of motion moving in the opposite direction for any motion detection system based on the EMD. (A) Data replotted from Figure 4 for normal phi motion (blue), superimposed with results from reverse-phi stimuli (red) collected in the same animals. (B) STAFs collected with normal phi apparent motion compared to those collected with reverse-phi stimulation in the same group of individual flies. Note that the EM-STAF is negative, indicating the reverse-phi illusion, but the FM STAF is essentially unaffected by the motion illusion. (C) Full-field yaw kernels measured for phi and reverse-phi motion collected from the same flies. By comparison, the “slices” of the EM STAFs at zero-degrees azimuth for the normal phi and reverse-phi stimuli are not equal in amplitude (arrowhead).