Crowding, the difficulty in recognizing a letter in close proximity with other letters, has been suggested as an explanation for slow reading in people with central vision loss. The goals of this study were (1) to examine whether increased letter spacing in words, which presumably reduces crowding among letters, would benefit reading for people with central vision loss and (2) to relate our finding to the current account of faulty feature integration of crowding.
Fourteen observers with central vision loss read aloud single sentences, one word at a time, using rapid serial visual presentation. Reading speeds were calculated based on the rapid serial visual presentation exposure durations yielding 80% accuracy. Letters were rendered in Courier, a fixed-width font. Observers were tested at 1.4× the critical print size (CPS), three were also tested at 0.8× CPS. Reading speed was measured for five center-to-center letter spacings (range: 0.5–2× the standard spacing). The preferred retinal locus for fixation was determined for nine of the observers, from which we calculated the horizontal dimension of the integration field for crowding.