The initial experimental evidence that resolution is indeed sampling limited was obtained under experimental conditions which avoided optical filtering of the retinal image by using interference fringes formed on the retina as a visual stimulus. When subjects were asked to increase the spatial frequency of the fringes until they could no longer resolve the pertinent details of the pattern, such as its orientation or spatial frequency, the cutoff frequency was very low - so low in fact that the subject would be considered legally blind. However, when the subjects were given a different task, namely to increase the frequency of the fringes until they were no longer visible, the cutoff frequency was very high, nearly as high as in foveal vision. This startling result prompted the phrase '20/20 at 20' meaning 20/20 detection acuity at 20 degrees in the periphery.

A quantitative comparison between detection acuity and resolution acuity is shown next.

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WWWaveTM 1996
World Wide Web automated virtual environment TM 1996
Kevin Haggerty, Indiana University.