Visual comfort as a criterion for designing display units

Display units designed for the transfer of alphanumeric information may be found to be quite different in quality. Badly designed units are not read easily and cause visual fatigue when used in long and intensive sessions. This has already received some attention (e.g., Grandjean, 1980; Padmos, this volume; Cakir, Renter, Schmude, & Ambruster, 1978; Cakir, Hart, & Stewart, 1979; Matula, 1981). It became apparent that it was important to match the physical parameters of the displays to the demands of the visual system. However, visual fatigue is known to be very difficult to measure and, consequently, is not an obvious design criterion. Looking for a more adequate measure, therefore, we surveyed other criteria based on two different angles of approach. The most direct candidate is the comfort with which a subject feels he can read the information on the screen. In principle this can be measured at least ordinally by psychometric methods. Another line of approach is the speed at which information is taken in, as reflected by performance measures like reading speed or by eye movement characteristics such as saccadic length and fixation duration.