Accomodation with displays having color contrast

Much concern has been expressed about the ability of the visual display terminal to provide adequate stimuli for accommodation. As a result it has been hypothesized that an observer may have to continually refocus to maintain accommodation on the display and this contributes to the visual fatigue experienced by VDT users. The increased use of multicolor CRTs in the workplace adds yet another factor, chromatic aberration, to affect the observers' accommodation to information presented on the CRT. Two experiments were run to determine the effect of viewing characters of one chromaticity and purity on a background of another chromaticity or purity or chromaticity and purity. The observer's accommodation response was continuously sampled throughout the presentation of each target/background combination. Mean accommodation response and the standard deviation of the mean accommodation response were then calculated to ascertain the effect the target background combination had on the observers' accommodation response. The observers' were also required to perform a visual performance task for each target/background combination.

The data collected indicate that chromatic characters when observed on chromatic background do not provide a strong stimulus for accommodation. Mean changes in the observers accommodation response were all within the depth of field except when characters were viewed on blue backgrounds. The variability in the observers accommodation response was not found to be a good predictor of image quality where only color contrast exists between foreground and surround. Task performance was highly correlated with effective contrast between the target and background as quantified by uniform color space modeling.