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Spatio-chromatic contrast sensitivity across the life span: interactions between age and light level in high dynamic range

We investigated the difference in spatio-chromatic contrast sensitivity between younger and older color-normal observers. We studied how the adapting light level affected the contrast sensitivity and whether there was a differential age-related change in sensitivity. Contrast sensitivity was measured for three chromatic directions, luminance levels from 0.02 to 2000 cd/m2, and different stimuli sizes using 4AFC method on a high dynamic range display. 21 observers with mean age of 33 and 20 older observers with mean age of 65 participated in the study. Within each session, observers were fully adapted to the fixed background luminance. Our main findings are: (1) Contrast sensitivity increases with background luminance up to around 200 cd/m2, then either declines in case of achromatic contrast sensitivity, or becomes constant in case of chromatic contrast sensitivity; (2) The sensitivity of the younger age group (<40 y.o.a.) is higher than that for the older age group by 0.3 log units on average. Only for the achromatic contrast sensitivity, the old age group shows a relatively larger decline in sensitivity for medium to high spatial frequencies at high photopic light levels; (3) Peak frequency, peak sensitivity and cut-off frequency of contrast sensitivity functions show decreasing trends with age and the rate of this decrease is dependent on mean luminance. The data is being modeled to predict contrast sensitivity as a function of age, luminance level, spatial frequency, and stimulus size.