Abstract
Purpose: :
People with bilateral central scotomas must use peripheral vision for reading. Depending on the pattern of central-field loss and the location of a preferred retinal locus, vertically oriented text may facilitate reading performance. In people with normal vision, reading speed in central vision is poorer for vertically oriented text than for horizontally oriented text. Yu et al (VSS 2008) found that differences were associated with a reduced visual span for vertical text. In the peripheral visual field, reading speed for horizontal text is also reduced in association with a reduced visual span. The current study investigated whether the differences between horizontal and vertical reading rates are also found in the peripheral visual field and whether there are corresponding differences in the visual span. These findings will be of significance for reading rehabilitation in people with central visual field loss.
Methods: :
Eight naïve normally sighted young adults participated in the experiment. All measurements were carried out with horizontal and vertical (rotated clockwise) lower case text presented in the central vision as well as at 10 degrees eccentricity. Vertical text was presented in the right and left visual field whereas horizontal text was presented in the upper and lower visual field. Reading speeds were measured using Rapid Serial Visual Presentation (RSVP). Visual Spans, plots of letter-recognition accuracy as a function of letter position were measured with trigrams (strings of three random letters). The size of the visual span was defined as the area under this profile, converted to bits of information transmitted.
Results: :
Reading speed and visual span were reduced for vertical text when compared to horizontal text, both in central vision and at 10 degree eccentricity (p< 0.01). Although overall reading speeds were lower in peripheral vision, the mean horizontal/vertical ratio was similar in central (H/V = 1.80) and peripheral (H/V = 1.59) vision. For both the reading speed and visual span no differences were found between right and left visual fields or inferior and superior visual fields.
Conclusions: :
The ratio of horizontal to vertical reading speeds were similar in central and peripheral vision, and were accompanied by similar differences in the size of the visual span.
Keywords: reading • low vision • age-related macular degeneration