Effects of chromatic and luminance contrast on reading

Reading performance was measured for drifting text defined by chromatic contrast with various amounts of luminance contrast present. With 0.12 luminance contrast added, reading performance was unaffected by the presence of chromatic contrast over a range of character sizes varying 30-fold. When luminance contrast was reduced to near the threshold for reading, chromatic contrast sustained reading rates of nearly 300 words per minute, almost as high as those found with high luminance contrasts. Low-pass filtering of chromatic text had a proportionately greater effect on small characters, as would be predicted from the lower bandwidth of chromatic visual channels. Arguments are presented suggesting that reading rates for equiluminant text are sustained by luminance transients introduced by transverse chromatic aberrations of the eye.