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The APPARATUS and the STIMULI (i.e., the targets) are described in Appendix A to the report. "APPARATUS: The rectangular viewing chamber was constructed of 1/2 inch plywood with outside measurements of 30 X 18 X 25 inches. The entire chamber was painted in flat black. The top of the chamber was removable, for easy access to stimulus arrangements. Mounted flush with the inside surface of the camber lid was a 9 & 1/2 inch milkglass surface rimmed with chrome, behind which was a lighting fixture, illuminated by a 100 Watt bulb. "Two 6 inch square viewing windows were cut in the chamber. The front window was positioned 7 & 1/2 inches from the top of the chamber and 5 & 3/4 inches from the right side. The second window was cut in the left side of the box, positioned 7 & 1/2 inches from the top and 6 inches from the front. "Three rows of 1/4 inch holes were drilled in the floor of the chamber, 6 inches, 12 inches and 18 inches respectively from the rear of the chamber. The stimuli were mounted in these holes in appropriate arrangement." "THE STIMULI: Two stimulus arrangements were prepared, so that the views from each of the two windows would be entirely different. "The stimulus arrangement for the front view consisted of three overlapping squares of different colors and sizes, arranged to give an illusion of depth. The square closest to the viewing window was painted red, and measured 5 inches square. It was positioned 5 & 1/2 inches from the right side of the chamber, 18 inches from the rear, and 11 & 1/2 from the floor, measured to the nearest surfaces. "The second square [behind the red square] was painted yellow, and the third square [behind the yellow one] was green.