Abstract
The purpose of our study was to investigate the difference in spatio-chromatic contrast vision between younger (below 40) and older (above 60) colour-normal observers. We were particularly interested in how the adapting light level affected contrast vision and whether there was a differential age-related change in contrast threshold as well as suprathreshold contrast matching. There are two parts of the study, (i) contrast threshold measurement, (ii) suprathreshold contrast matching. In threshold measurement task, contrast sensitivity was measured for Gabor patches of 5 spatial frequencies (0.5, 1, 2, 4, and 6 cpd) in achromatic and two chromatic directions, at background luminance levels ranging from 0.02 to 10,000 cd/m^2. In the contrast matching task, a reference stimulus was displayed at a fixed luminance level and observers adjusted the contrast of the test stimulus displayed at different luminance levels (0.02 to 2000 cd/m^2). The matching experiment was repeated for 0.5, 2, and 4 cpd for all three colour directions at three suprathreshold levels of increasing contrast. Our main findings are: (1) Contrast sensitivity increases with background luminance up to around 200 cd/m2, then either declines in case of luminance contrast sensitivity, or becomes constant in case of chromatic contrast sensitivity; (2) The sensitivity of the younger age group is higher by ~0.3 log units; (3) Contrast sensitivity at higher spatial frequencies is more affected by ageing; (4) The differences between old and young group are not carried over to suprathreshold levels. Our results show that the effect of age on suprathreshold contrast matching is small in comparison to the age-related decline in contrast sensitivity (Mei et al, 2007) which is consistent with the hypothesis that contrast sensitivity at threshold is limited by different factors than suprathreshold vision.