Résumé : | SIGNIFICANCE: Contrast sensitivity changes across the visual field with age and is often measured clinically with
various forms of perimetry on plain backgrounds. In daily life, the visual scene is more complicated, and therefore,
the standard clinical measures of contrast sensitivity may not predict a patient's visual experience in more natural
environments.
PURPOSE: This study aims to determine whether contrast thresholds in older adults are different from younger
adults when measured on a 1/f noise background (a nonuniform background whose spatial frequency content is
similar to those present in the natural vision environments).
METHODS: Twenty younger (age range, 20 to 35 years) and 20 older adults (age range, 61 to 79 years) with normal
ocular health were recruited. Contrast thresholds were measured for a Gabor patch of 6 cycles per degree (sine
wave grating masked by a Gaussian envelope of standard deviation 0.17°) presented on 1/f noise background
(root-mean-square contrast, 0.05 and 0.20) that subtended 15° diameter of the central visual field. The stimulus
was presented at four eccentricities (0°, 2°, 4°, and 6°) along the 45° meridian in the noise background, and nine
contrast levels were tested at each eccentricity. The proportion of correct responses for detecting the target at each
eccentricity was obtained, and psychometric functions were fit to estimate the contrast threshold.
RESULTS: Older adults demonstrate increased contrast thresholds compared with younger adults. There was an
eccentricity-dependent interaction with age, with the difference between groups being highest in the fovea compared with other eccentricities. Performance was similar for the two noise backgrounds tested.
CONCLUSIONS: Our results revealed a strong eccentricity dependence in performance between older and younger
adults, highlighting age-related differences in the contrast detection mechanisms between fovea and parafovea for
stimuli presented on nonuniform backgrounds. |