Art Dealers’ Optical Test #1: When Peter Nagy of Nature Morte looks at the square, the near circle appears double. The reverse is true when the circle is fixated.

Art Dealers’ Optical Test #2: To Colin de Land of American Fine Arts, the string appears single wherever it is fixated, double elsewhere.

Art Dealers’ Optical Test #4: Helene Winer of Metro Pictures points to rectangle that appears to match one held up by gallery partner Janelle Reiring at each testing distance.

Art Dealers’ Optical Test #6: Light Directed from the side through the closed lid of Oliver Wasow of Cash/Newhouse Gallery will cast a shadow of the retinal blood vessels that can be seen with careful observation.

From ‘The art dealers’ optical tests’ (1987) by David Robbins