Traditional media is gradually being replaced by new media with digital information technology, and digital reading has become a new choice for older adults to learn knowledge and information. However, the deteriorating vision and declining energy of the elderly lead to higher requirements for the readability and legibility of the text interface. Compared to traditional reading media, digital reading adds carriers (e.g., audio, video, and tactile feedback), improves the quality of picture information, and more importantly, provides flexible and variable text layouts to adapt to different types and sizes of display interfaces.

The purpose of this study is to investigate the effects of font size, spacing (e.g., word spacing, line spacing), and margins in text interface factors on digital reading for the elderly. The study designed reading materials with different combinations of factor levels according to an orthogonal experimental protocol. Reading performance data were collected respectively from the older and younger subjects through an eye-tracking device and a post-measurement scale. The experiment was evaluated in two dimensions, including cognitive load and user experience. Cognitive load indicators included total gaze time, number of gaze points, and pupil diameter. The user experience indicators included subjective comfort and usability scores. Among the cognitive load indicators, the total gaze time and the number of gaze points reflect the subjects'effort, and the larger the value of these two indicators, the more easily people are fatigued, indicating that their cognitive load is higher. On the contrary, the larger the value of pupil diameter, the more relaxed people are, and the lower their cognitive load is. The usability score reflects the user's evaluation of the usability of the text interface, and a higher score indicates that the user approves of the product; while subjective comfort intuitively reflects the user's perception of their comfort and fatigue level.

Combining objective data records and subjective evaluations for data analysis, the analysis results showed that there was no significant difference between the digital reading performance levels of the elderly and the young, except for pupil diameter. The objective data showed that the performance level of the elderly was lower, but the subjective evaluation of digital reading was higher among the elderly. The factors that had the greatest effect on digital reading among older adults were margin and font size, both of which had higher performance on different indicators. Word spacing and line spacing had a smaller effect on older adults'reading performance, but there were significant interactions between the two and other factors. Older adults'reading performance showed a non-monotonic trend with increasing levels of each factor, i.e., there was an ideal range of factor levels that made users perform best on a particular indicator.

The study explored interface factors and their levels that affect older adults'digital reading. By comparing the differences in reading experience and performance between younger and older adults, it was found that although older adults do not perform as well as younger adults, they have a higher level of acceptance to digital reading. Previous studies have shown that font size affects the efficiency and experience of digital reading for older adults. Surprisingly, this study found that page margins also have a significant effect on digital reading for older adults, which had been rarely examined before. These findings suggest that different text interface factors have different effects on older adults'digital reading, and that seniors can benefit more from digital reading with a reasonable design of text interface.