<title>Task performance and contrast polarity on hard copy and video displays</title>

Abstract

Performance was measured on an editing task which required counting the number of occurrences of an assigned letter in a paragraph of random letters. The task was presented in three different display modes: (a) a video display (VDT) with white characters on a black background, (b) a white-on-black photograph of the VDT display, and (c) a black-on--white photograph of the VDT task display. The viewing conditions for the three display modes were matched. Defocus was introduced by cylindrical lenses (simulated astigmatism) and by plus lenses. Performance was measured by time and accuracy in completing the counting task. There were 19 normally-sighted young adult subjects tested with the task in the three display modes under 6 levels of defocus.For the hard copy displays, performance was significantly faster (on average by 6.6%) for black characters on a white background. Performance with the black background photographs was consistently, but marginally (0.9%), faster than with the VDT displays. Cylindrical defocus of 1.50 diopters substantially impaired efficiency, but low-power plus lenses did not affect performance.

The effects of induced oblique astigmatism on symptoms and reading performance while viewing a computer screen

“…Limitations of the present study include the small sample size and the short task duration. While a significant increase in post‐task symptoms was observed, the finding of no significant change in reading speed with up to 2D of astigmatism is consistent with previous findings 14,15 . Indeed, a post‐hoc power analysis demonstrated that the sample size would have to be increased to over 174 subjects for the size of the change in reading rate with induced astigmatism observed here to become significant.…”

“…This result is similar to the observations of Sheedy et al. 14 Their investigation examined the effect of up to 1.50D of induced astigmatism (minus axis 90°) on task performance during an editing task which required counting the number of times an assigned letter occurred in a paragraph of text. They also compared hardcopy printed text having either a black‐on‐white or white‐on‐black polarity with a computer screen having a white‐on black display.…”

“…Interestingly, the investigation of Sheedy et al. 14 which required subjects to count the number of times an assigned letter occurred in a paragraph of text found similar results, namely that 1.50D of induced astigmatism had minimal impact on either performance time or the number of errors per trial. Additionally, a recent study suggested that Rasch analysis of the OSDI findings may be superior to the Likert scoring method used here 26 …”

The visual and functional impacts of astigmatism and its clinical management

“…115 A significant reduction in task performance of a computer based editing task (increased task completion time and number of errors) was also found to occur with 1.50 D of induced astigmatism. 116 These findings indicate that uncorrected astigmatism has the potential to impact a number of different common occupational visual tasks, particularly tasks with a high acuity demand.…”