The influence of level and polarity of figure-ground contrast on vision

Abstract

Purpose: To document the effect upon human foveal vision of changes in the level and polarity of figure-ground contrast under photopic controlled test conditions, with particular emphasis on performance at low contrast levels.

Methods: Using a forced-choice psychophysical paradigm, threshold acuity estimates were derived at 9 discrete levels over a near-3 octave contrast range for Landolt ring-type stimuli of either positive or negative polarity. Data were obtained under binocular conditions from 10 young adults, each wearing their optimum low myopic spectacle correction.

Results: Visual acuity declined linearly with reducing stimulus contrast, the deterioration increasing substantially at <10% figure-ground contrast regardless of stimulus polarity. Performance was slightly (but not statistically significantly) better for positive contrast stimuli.

Conclusion: Irrespective of contrast polarity, a reduction in stimulus figure-ground contrast <10% produces an accelerated decrement in photopic foveal vision compared to the performance at levels >10%. Some clinical and practical implications of this outcome are considered with regard to the examination of patients with normal and compromised visual function.