Figure 4.

(a) The same sequence as the one shown in Fig. 3b, except the occluders are explicitly defined by contrast differences. (b) A sequence with subjectively defined occluders. (c) The dominant percept with sequences a and b: a partially obscured diamond translating horizontally behind three opaque strips. (d) A comparison of the results obtained with the sequence shown in Fig. 3b and sequences a and b shown here. The explicit indication of occluding surfaces (contrast defined or subjective) strongly biased the percept from being one of motion in the vertical direction to one of coherent horizontal motion. Both the contrast and subjectively defined occluders generated a much stronger bias for perceiving coherent horizontal motion when compared with the display that contained only the moving contour segments (pairwise t test, P < 0.001).