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Visual Cognitive Performance of Elderly People~Effects on Reading Time of Age, Character Size and Visual Distance
Published October 22, 2006 by Society of Automotive Engineers of Japan in Japan
In the design of the onboard visual information displays used in vehicles, it is necessary to consider the decrease in information processing performance that occurs with age. For this reason, an attempt was made to quantitatively clarify the relation between age and reading performance.
Namba (1983) has reported on the reading speed for Japanese characters. Japanese phrases were converted to the number of characters read in kana (a Japanese syllabary), and the amount of information per kana character was defined as 6 bits. Furthermore, experiments have shown that the average reading speed is 50 bits/s. On the basis of these findings, two experiments were conducted to clarify the relation between age and reading performance for Kanji characters.
Experiment 1: Kanji characters were randomly displayed in two-character compounds on a computer screen. The number of Kanji characters was changed in three steps, and the relation between the gazing time for reading and the number of characters was investigated in 100 subjects with ages ranging from their 20's to 80's. All the Kanji characters were large enough to be visible for elderly people. The displayed characters were converted into the information value (bits) according to the method of Namba. The gazing time was divided into the preparation time and information processing time, and the information processing speed was calculated from the amount of information read divided by the information processing time. The information processing speed was found to be 50 bits/s in all age groups, a speed that showed the best agreement with Namba's report. The preparation time tended to increase with the square of age, the reason for which was considered to be the decline of accommodation performance with age. A formula that can estimate the relation between gazing time and the amount of displayed information for every age is proposed.
Experiment 2: Kanji characters were displayed in a manner similar to experiment 1. The character size was changed between three conditions (large, middle and small), and visual distance was changed between two conditions (700 and 2000 mm). The gazing time was also similar to that in experiment 1. The results showed that character size influences preparation time but did not have a great effect on information processing speed. Longer visual distance reduced the preparation time but did not change information processing speed for all age groups. All these influences were explained by the visual demands of character size and visual distance compared with accommodation performance.
These results are applicable to the design of user-friendly information devices, taking into account the user's age.