In reading text that is automatically scrolling vertically, the vertical gaze position is important because it indicates the relation between the scrolling speed and reading speed. We investigated this gaze position at a speed comfortable for the reader. We also investigated the effect of presenting limited information about the text below the text presentation area.

The results showed that participants gazed most frequently at the bottom line in the four-line display, and at the central line in the seven-line display. This suggests that the slower comfortable reading speed for the four-line display is related to reading at the bottom line. Presenting information below the text presentation area did not affect the comfortable reading speed nor the fixation duration. This suggests that the perceptual span of reading texts scrolling automatically does not extend below the reading line.

There is a phenomenon called visual persistence, in which a briefly presented visual stimulus seems to remain for a while after it disappears. Previous study (Bowling and Lovegrove, 1981)¹⁹⁾ reported that the length of visual persistence was not significantly different for vertical lines than for horizontal lines, while others (Hirakawa and Kanazawa, 2022)²⁰⁾ reported that the length of visual persistence was significantly different for vertical lines and horizontal lines. However, both studies rarely mentioned the factors that cause the difference in duration length. In the present study, we investigated the effects of the orientation of stimuli (vertical vs. horizontal), the interstimulus interval and the number of stimuli presented on stimulus discrimination and location detection as the measures of visual duration. One group was presented with a total of 3 stimuli, while the other group was presented with a total of 15 stimuli. We revealed that the number of stimuli affected the length of visual persistence of vertical and horizontal lines in both stimulus discrimination and location detection tasks. These results suggest that the “process theory” that the length of visual persistence was determined based on an active process of information storage.