The Effect Of Letter String Length On The Size Of The Visual Span And Reading Speed.

Background: The visual span has been defined as the number of letters that can be correctly
discriminated at and around fixation without executing an eye movement. Legge, et al (2007),
have implied that the visual span is one of the sensory bottlenecks that limit reading speed. This
study investigated the effect of increasing string length on the size of the visual span and its effect on reading speed. Methods: The visual span was measured on 15 college-level subjects with both random trigrams and pentagrams. Reading speeds were measured using 3 letter words and 5
letter words that were randomly presently using the flashcard paradigm (FC) and the Rapid Serial Visual Presentation method (RSVP). Results: The reading span decreased by approximately 40% (Paired t( 14) = 3 0 .44, p < 0. 001) when measured with pentagrams as opposed to the reading span measured with trigrams. A Two-Way ANOVA showed no significant effect of string length on reading speed (F(1,59) = 2.72, p = 0.104), no interaction effects between reading condition (RSVP or FC) and string length (F(1 ,59) = 0.165, =0.686), but a significant effect of reading condition (RSVP vs. FC; F(1,59) = 30.36, p < 0.001). Conclusions: Higher level reading processes can compensate effectively when low-level information in the visual span is significantly compromised or attenuated in normal readers.