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Deyue Yu, David Gerold, Gordon E. Legge, Allen M. Y. Cheong, Heejung Park; Size of the visual span may explain reading-speed differences for horizontal and vertical text. Journal of Vision 2007;7(9):517. doi: https://doi.org/10.1167/7.9.517.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous research has shown that reading speed is substantially reduced by arranging letters in words vertically compared with the normal horizontal arrangement. According to an experiential hypothesis, the difference occurs because most English speakers almost always read horizontal text and seldom read vertical text. We have explored an alternative perceptual hypothesis. It has been proposed that the size of the visual span—the number of letters recognized reliably without moving the eyes—is a visual factor limiting reading speed. We hypothesized that reduced visual-span size in the vertical direction accounts for the reduced vertical reading speed.
Methods: Five normally sighted adults participated. Visual span profiles, plots of letter-recognition accuracy as a function of letter position left or right (horizontal arrangement) and above or below (vertical arrangement) the midline, were measured with trigrams (strings of three random letters). Size of the visual span was defined as the area under this profile, converted to bits of information transmitted. Reading performance was measured using RSVP (Rapid Serial Visual Presentation) for horizontal and vertical words.
Results: The mean horizontal reading speed was 524 wpm, and was 1.7 times greater than the mean vertical reading speed. As predicted by the Perceptual hypothesis, the mean horizontal visual span (42 bits) was larger than the mean vertical visual span (35 bits). Based on the relationship between visual-span size and reading speed in other studies, a difference of 7 bits in the visual-span size is expected to produce a difference in reading speed by a factor of 1.6 which is close to the observed value.
Conclusions: Our results indicate that a perceptual explanation may account for the difference in horizontal and vertical reading speed. These results do not exclude the possibility that both the size of the visual span and reading speed are influenced by reading experience.
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