In Experiment I, performance on a conventional (full) rod and frame was compared with that on three other displays. These included a closure condition in which only the corners of a luminous frame were present, a subjective contour condition in which the rod was seen against a black square subjective surface, and a pattern condition in which four luminous disks were arranged to form the corners of a square pattern. In all cases, a square-like form was perceived. The rod-and-frame effect (RFE) was greatest on the full frame, which differed significantly from an the rest. Closure produced the next greatest influence, while the responses to subjective and pattern conditions did not differ from each other. Experiment 2 showed that a subjective frame was no more effective than the subjective surface of Experiment I, and verified the importance of 90-deg corner elements in the rod-and-frame display. The conclusion drawn was that equivalent form organizations are not sufficient to produce equivalent levels of the RFE, but certain luminance-difference contours appear to be essential. Figure I. All the display elements were made of electroluminescent panels and were shown with a luminance somewhat under I nit. The full frame was 101.6 cm in length and 2.5 cm wide. The rod dimensions were 96.5 x 2.5 cm and were identical in all conditions. In the closure condition (Figure 1b), the outer edge of each corner was 9.6 crn and this also was the dimension of one