Figure 3.

(a) The setup used to generate the sequence shown in b. The diamond oscillated horizontally behind occluders that had the same gray level as the background. There is no physical significance to the depth differences among the occluders, diamond, and background shown in this figure. They are indicative only of the relative depth ordering used to generate the sequences. The displays subtended 7° of visual angle at a viewing distance of 80 cm. The diamond’s speed of oscillation was 0.7°/s. (c) The setup used to generate the sequence shown in d. The four point features attached to the moving diamond serve to disambiguate its motion. (e) The percept with sequence b—four lines oscillating vertically. No occluding contours are perceived. (f) The percept with sequence d. The four lines are seen as being part of a partially occluded diamond translating horizontally; strong subjective contours are reported at the indicated locations. As shown in the enlarged Inset, the illusory contours coincide with the discontinuities in the horizontal motion field. The reported contours were not precisely vertical but were slightly curved, possibly due to a bias toward orthogonality to the inducing contour. (g) A summary of the results obtained with the two sequences.