Supra‐threshold contrast matching and the effects of contrast threshold and age

Abstract

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.

Key words:

• age
• contrast constancy
• contrast matching
• contrast sensitivity
• contrast threshold

ACKNOWLEDGEMENTS

This research was supported by the Macular Disease Society, UK. We would like to extend thanks to Trefford Simpson for help in the use of Morphonome.