The Effects of Letter Design Features and Aging on Legibility.

We examined how letter legibility is affected by letter design features (size, contrast, font-type, and complexity), and how this changes with age (by comparing younger [ N = 54] and older participants [ N = 54]). Types of letters in the study were Japanese characters, Latin alphabets, and digits. Participants verbally reported the letter presented on a Cathode Ray Tube (CRT) display in natural viewing conditions. The legible-contrast threshold was calculated as the contrast boundary of 50% correct answer. We found that letter complexity (i.e., number of strokes) did not affect legible contrast threshold, except for small (<0.35°) letters. Moreover, letter size even affected the threshold with a function similar but not identical to contrast sensitivity function. This supports the previous hypothesis proposed by Majaj et al. that optimal spatial frequency band exists for letter identification and shifts with its size. Another novel finding was the effect of aging on the legible-contrast threshold and how it related to other letter features. Constant aging effect on legible-contrast was found across letter sizes. Among older adults, the legible-contrast thresholds were 1.2 to 2 times those of younger adults. Moreover, the aging effects were greater for positive-contrast than for negative.

Toward a CIE supplementary system of photometry: brightness at any level including mesopic vision.

Photometry for brightness at any level including mesopic vision is described on the basis of the work conducted towards the development of a Commission Internationale de l'Eclairage (CIE) supplementary system of photometry in CIE technical committees. Several critical items in developing such a system are discussed: (1) how to scale brightness using the concept of equivalent luminance; (2) the basic vision model of brightness perception; (3) a description of the chromatic contribution to brightness at the photopic as well as at the mesopic level; (4) formulation of an adaptation coefficient for rod-cone interaction. A possible photometric model for brightness is described based on these considerations, together with a quantitative evaluation of the model using experimental data.