Psychophysics of reading--V. The role of contrast in normal vision.
How does contrast affect reading rate? What is the role of contrast sensitivity? We measured reading rate as a function of the contrast and character size of text for subjects with normal vision. Reading rates were highest (about 350 words/min) for letters ranging in size from 0.25 degree to 2 degrees. Within this range, reading was very tolerant to contrast reduction--for 1 degree letters, reading rate decreased by less than a factor of two for a tenfold reduction in contrast. The results were very similar for white-on-black and black-on-white text. Reading rate declined more rapidly for very small (less than 0.25 degree) and very large (greater than 2 degrees) letters. People with low vision usually require large characters to read, so high contrast is particularly important for them. Taking 35 words/min to be a threshold for reading, we constructed a contrast-sensitivity function (CSF) for reading. We were able to relate the shape of this CSF to the shape of sine-wave grating CSFs.
Legge
G E
GE
Department of Psychology, University of Minnesota, Minneapolis 55455.
Rubin
G S
GS
Luebker
A
A
D006801:Humans; D008027:Light; D011601:Psychophysics; D011932:Reading; D012684:Sensory Thresholds; D013028:Space Perception / Q000502:physiology*; D013997:Time Factors; D014796:Visual Perception / Q000502:physiology