© 2007 The Authors Journal compilation © 2007 Optometrists Association Australia Clinical and Experimental Optometry 90.4 July 2007 272 CLINICAL AND EXPERIMENTAL OPTOMETRY Clin Exp Optom 2007; 90: 4: 272–281 DOI:10.1111/j.1444-0938.2007.00162.x Key words: age, contrast constancy, contrast matching, contrast sensitivity, contrast threshold The use of achromatic sine-wave gratings with varying spatial frequencies is an effi- cient tool to study contrast perception. It is known that contrast perception be- haves differently at threshold and supra- threshold levels. 1 Research on contrast threshold with varying spatial frequencies has shown that the maximum contrast sen- sitivity is at two to five cycles per degree (cpd). 2–6 Factors such as grating area, duration time, mean luminance and reti- nal location have a significant effect on contrast threshold. 6–13 It could be argued that studies of supra-threshold contrast perception give us more information about our day to day visual perception. Supra-threshold contrast matching functions (CMFs) have decreasing spatial frequency dependency with increasing contrast. At higher contrast they take the shape of a wide band-pass or become flat. 1,6,14–17 This phenomenon was termed ‘contrast constancy’ 1 and holds for a wide range of spatial frequencies and retinal eccentricities. Because of this contrast constancy, we perceive objects at a con- stant contrast regardless of the size and distance. Several studies have demon- strated conditions under which contrast constancy breaks down. Peli and co- workers 6 tested CMFs under natural view- ing conditions, showing that below 8 cd/ m 2 , contrast matching is dependent on luminance. Legge and Foley 18 agree that contrast processing above 10 per cent con- trast is the invariant with number of grat- ing cycles. With dichoptic presentation and a long duration of light adaptation, Hess 19 showed that at very low luminance (less than 0.02 cd/m 2 ) and higher spatial frequencies (10 cycles/degree), there were substantial deviations from contrast Ming Mei MD MSc Susan J Leat PhD FCOptom FAAO Jeffery Hovis OD PhD FAAO School of Optometry, University of Waterloo, Waterloo, Canada E-mail: m2mei@uwaterloo.ca Background: The effects of age on contrast threshold are well known but little is known about its effect on supra-threshold contrast perception. This study examines supra- threshold contrast matching and the effects of age in naïve observers. Methods: Two age groups (from 20 to 50 years with 14 subjects and 51 years and older with 15 subjects) participated in the study. Contrast threshold and supra-threshold contrast matching up to 8.53 cycles per degree were measured. Results: Both age groups demonstrated some degree of contrast constancy at medium and higher contrasts but this was not perfect even at the highest contrast tested (55.9 per cent). There was no overall effect of age on supra-threshold contrast matching (p = 0.086) but there was an interaction between age and spatial frequency (p < 0.001). The plots of matched contrast against standard contrast showed that for some spatial frequencies, the slope was significantly different from unity, indicating a gain in the visual system for supra-threshold perception. This was still true when corrected for threshold differences. Conclusion: Contrast constancy exists in a larger group of naïve subjects of different ages but does not perfectly compensate for the differences in thresholds. The results are discussed in terms of the currently proposed models of contrast perception. Supra-threshold contrast matching and the effects of contrast threshold and age Submitted: 30 October 2006 Revised: 8 February 2007 Accepted for publication: 2 March 2007