Abstract
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 2000mm). 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.
Keywords - Reading time, Elderly people, Visual display, Visibility, Accommodation