Ken Sagawa

Spectral luminous efficiency functions in the mesopic range

Spectral luminous efficiency functions for mesopic vision were measured extensively to establish a basic data set for the mesopic photometry system. These functions were obtained by the direct brightness matching for a 10 degrees field at nine retinal illuminance levels from 100 to 0.01 Td in 0.5-log-unit steps. Data for 12 subjects were collected. In the mesopic range, the spectral luminous efficiency function, averaged over 12 subjects, gradually changes form with retinal illuminance. This suggests that the mesopic function should be established for all the levels in that range. An attempt was made to find an empirical formula that expresses the mesopic function as a simple combination of the photopic and the scotopic brightness functions.

System of mesopic photometry for evaluating lights in terms of comparative brightness relationships

A photometric system assessing lights in the mesopic range in terms of comparative brightness relationships is described. The system is based on a weighted geometric mean of the CIE photopic luminance modified by the brightness-to-luminance ratio (B/L) and the CIE scotopic luminance to provide an equivalent luminance that corresponds to comparative brightness relationships of lights in the mesopic range. The weighting coefficient, called the adaptation coefficient, is defined as a function of equivalent luminance, so an iterative calculation is required to obtain an appropriate equivalent luminance. Examples of how to calculate the equivalent luminance and an experimental evaluation of the system are described.

Spectral luminous efficiency as a function of age

Spectral luminous efficiency function for a 2-deg field at a photopic level (100 Td) was measured for 91 observers by flicker photometry (FP) and for 97 observers by direct brightness matching (DBM), to find age-related change in the efficiency function as well as to obtain a reliable data set to be used in photometry. Observers ranged in age from 11 to 78 years. A gradual reduction of luminous efficiency with age was observed for both functions by FP and by DBM in the short-wave region, which was expected because of the age-related increase of optical density of eye lens. A similar age-related reduction of efficiency was observed in the long-wave region for the function obtained by DBM; this reduction was regarded as being due to reduced chromatic contribution to brightness with age. Principal components analysis on the spectral efficiency data and an analysis of the efficiency difference between the data obtained by DBM and FP confirmed this conclusion. Assuming a log-linear change in efficiency with age for any wavelength throughout the life span, spectral luminous efficiency function at any age was derived for photometric use.

Psychophysical methods for assessing visual comfort for a colored pattern of natural environment

Humans visual comfort to a colored image of a natural scene presented on a CRT display was investigated by two psychophysical methods. One was to measure a number of colors contained in an image by using the categorical color naming technique and to correlate it to the subjective estimation of visual comfort. The other one was to find an optimum percent chroma for a whole image by continuously adjusting the chroma value of all the pixels in the image relatively from zero (achromatic image) to 100% (original chroma) and to correlate it also to the comfort estimation value. Experimental results show that both variables strongly correlated to the subjective estimation of comfort; that is, a negative correlation between the comfort estimation and the number of categorical colors, which means the larger the number of colors contained in an image, the less comfort the image is felt to have, and a positive correlation between the comfort estimation and the optimum percent chroma means that the less comfort pattern is apt to be seen in a reduced chroma while the comfort pattern remains in original chroma. These findings suggest that the visual comfort could be evaluated by the number of categorical colors in an image and the relative amount of chroma of a whole image.

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.

Time Reduction Design Method for Cognitive Assist Technology

Given the importance and abundance of current visual information, visual display designs should consider their accessibility to elderly people. However, adapting designs not only to young users but also to older users is difficult because the difference in perception and cognition between these age groups remains unclear. In order to solve this accessible design issue, we introduce three studies: a study on the effect of aging on visibility, the construction of a database containing the sensory characteristics of older persons and persons with disabilities, and experimental and conceptual studies of our proposed design method, the time reduction design. The time reduction design method can solve the cognitive problems of aging societies by improving both spatial visibility and recognition speed.

Aging Effects of Inner Character Space and Line Space of Japanese Language

This study used Japanese sentences to investigate how inner character space, line space, and reader age differences affect readability. Results can suggest good layout of sentences for older adults. Japanese sentence experiments revealed that adequate inner character, line space, and number of characters provide good readability.

Standardization of “Dynamic Sign” for Comfort and Safe Society

Animated signs and signs that changed according to the situation, can be expected to improve the convenience of facilities and improve safety and security concerning traffic. This technology is already being developed in multiple countries, and some practical applications have already been realized. Most of these consist of projection lighting systems for presenting information in public spaces. In this paper, this technology will be referred to as “Dynamic sign.”

Accessibility and Standards in Japan —Historical Overview and the Future—

Accessibility is one of the social keen issues in Japan. This social concern reflects Japanese Industrial Standards Committee, JISC, to develop more than 40 accessibility-related standards (JISs) by now for solutions of various problems that older people and people with disabilities have. Ergonomic knowledge and data are addressed as critical points that make JIS standards successful. Fundamental design methods such as color combination, font size, tactile markings, etc. were developed by taking account of effects of aging and disabilities. Some of them have been proposed for ISO standards to make international contribution of JISC with Japanese experiences in developing accessibility standards. These history and future issues are described here.

Considerations of contrast sensitivity function of low vision

For people with low vision, contrast is extremely important to comprehend visual information of products and signs. For better design of products and services, this study is aimed at establishment of a database of contrast sensitivity functions (CSFs) of people with low vision. The CSFs of participants (72 people with low vision) were measured. The measured contrast sensitivity function showed large variation among individuals—ranging from the normal sensitivity level to a much lower level—with no representative function, but revealing a clear sensitivity decrease at the higher spatial frequency region greater than 1 cpd when compared with data of normal younger and older people. Results show that spatial discrimination of detailed objects is much worse for people with low vision. The data analyses were conducted along with classification using medical tests.