The effects of optical vergence, contrast, and luminance on the accommodative response to spatially bandpass filtered targets.

The steady-state monocular accommodative response was measured using a new type of stimulus, a spatially bandpass filtered luminance distribution known as a difference of Gaussian or DOG. The independent variables were: spatial frequency, optical vergence, contrast, and mean luminance. High-contrast DOGs of varying peak spatial frequencies were presented monocularly over a range of target optical vergences. In addition, DOGs were presented at a fixed dioptric vergence (1) over a range of contrasts with a constant mean luminance, and (2) over a range of mean luminances with a constant contrast. The magnitude of the accommodative error was found to depend on the total stimulus condition, i.e. the particular level of each independent variable. Changes in retinal-image contrast from the background (zero-defocus) level, which were brought about by the errors of accommodation under the various stimulus conditions, were mathematically determined and were used to calculate the "accommodative (contrast discrimination) Weber fractions". Comparisons between accommodative and psychophysical contrast discrimination data revealed that there are limits to the degree of shared processing of contrast discrimination information between accommodation and visual perception.