Retinal image noise and vernier acuity

The effects of optically produced "noise" in the retinal luminance distribution of a vernier stimulus are demonstrated in two experiments. In the first, vernier performance with a bright, two-dot target is shown to improve upon the introduction of a luminous background field, relative to performance with a completely dark background. The brighter background probably acts as an adapting field, reducing the visibility of the retinal image "noise". The second experiment demonstrates that, under defocused conditions, introduction of a low-pass spatial filter that removes phase-reversed high spatial frequency components can enhance vernier performance. Thus, high spatial frequency information may interfere with the vernier response when phase information is disturbed by defocus.