Visual discrimination on colour VDTs at two viewing distances

Abstract

The paper describes a research study on visual discrimination of textual and graphic symbols on a visual display terminal (VDT) screen when viewed at eye-lo-screen distances of 61 cm and 152 cm (24 and 60 ins). Conducted as part of a development programme at McDonnell Douglas Corporation's St. Louis Aircraft Company for an Integrated Manufacturing Composites Centre (ICC), the study investigated symbol shapes, symbol sizes, symbol colours and background colours at the two viewing distances. The longer distance is representative of required placements of the VDTs at some manufacturing workstations to avoid interference with process or control equipment. Knowledge gained from the study was incorporated in the selection of the manufacturing computer information system (CIS) terminals.

All four treatments showed significant effects on visual discrimination at both viewing distances and, particularly at the 152 cm distance, the mix of symbol and background colours was highly significant. A black screen background colour with more luminous symbols such as orange, green, yellow provided much better visual discrimination at the extended viewing distance than less luminous symbols such as red and blue on a white background. Visual discrimination at the extended viewing distance, when compared with the shorter viewing distance and using symbols of equal size, was better than the loss in visual angle would suggest.

Sex and age (to age 65) did not significantly affect visual discrimination mean scores, but the variance among individuals in the 51-65 years age group was greater than for the younger age groups.

The visual discrimination scores for symbol sizes of 4 mm² were not significantly different from the 6 mm² symbols at the 61 cm viewing distance. The 4 mm² symbol size was therefore adequate for visual discrimination of standalone symbols at this distance. Although 8 mm symbols were not used in this study, projections from the data indicate that such symbol sizes at 152 cm would provide comparable discrimination scores to the 4 mm² at 61 cm.

Improved visual discrimination of standalone symbols occurs with gaps or changes in the angles of symbols, such as sets ‘C’ versus ‘O’ and ‘Xl’ versus‘+’.