The Effect of Contrast Reversal on Peripheral Visual Acuity

Patients with central vision loss must rely upon regions of their unaffected peripheral retina to carry out fine-scale visual tasks. We aimed to determine the conditions under which contrast reversal of targets and/or backgrounds may act to improve visual acuity in the peripheral field.

Ten participants with normal or corrected-to-normal vision performed a visual acuity task in which they were asked to identify the orientation of a letter-C target presented at 10° in the right visual field. Minimum letter size thresholds were measured for static (black or white) and contrast-reversing (8.5 or 17 Hz) targets presented on a uniform mean luminance background, a static patterned background, or a dynamic version of the patterned background, which was contrast reversing at the same temporal frequencies used for the targets.

When presented on a uniform background, black targets produced lower thresholds than white targets, and there was no consistent benefit of contrast reversal. However, when presented on a patterned background, acuity for contrast-reversing targets consistently exceeded that for either polarity static target. Contrast reversing the background also improved acuity, for both static targets and targets that contrast reversed at a different rate.

Peripheral visual acuity is significantly enhanced by dynamic contrast modulation, particularly when the modulation acts to promote segmentation between target and background.

Adding temporal modulation to the target or background could provide a simple way of enhancing peripheral acuity for patients with central vision loss.