Three experiments were conducted in which positive and negative contrast on visual display terminals were directly compared. Operator tasks included visual search and reading, with accuracy and timeliness of response measured. In all cases where significant differences exist, better performance was obtained with negative contrast (dark characters or symbols on a lighter background). The increases in performance range from a low of 2.0 percent to a high of 31.6 percent. Based on the above results, we believe that there are significant advantages in visual task performance obtained from the selection of negative contrast displays.Current standards that require negative contrast appear to be justified, while future revisions of ANSVHFS 100-1 988 and other standards should seriously consider incorporating negative contrast as a recommendation or requirement.

This study investigated how rotation of dot-matrix characters influenced human performance, measured by the response time in a random search task. Factors that influence the extent of dot-matrix pattern distortion were identified, and their effects were investigated. Significant effects were found in angle of rotation (p=0.0046; 0 to 180 degrees in a 5-degree increment), target character's distance from the center of rotation (p<0.0001), and target characters (p<0.0001). Issues pertinent in predicting the effect of dot-matrix pattern distortion on performance are discussed.

This study was conducted to investigate the effects of display failures and rotation of dot-matrix symbols on visual search performance. The type of display failure (cell, horizontal line, vertical line), failure mode (ON, failures matched the symbols; OFF, failures matched the background), percentage of failures (0, 1, 2, 3, 4%), and rotation angle (0, 70, 105 degrees) were the variables examined. Results showed that displays which exhibit ON cell failures greater than 1% significantly affect search time performance. Cell failures degrade performance more than line failures. Search time and accuracy were best when symbols were oriented upright. The effects of display failures and rotation angle were found to be independent. Implications for display design and suggestions for quantifying the distortion due to rotation are discussed.