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Abstract
The visual span in reading is the number of characters that can be recognized at a
glance. The shrinking visual span hypothesis attributes reading deficits in low vision,
and slow reading in normal vision at low contrast, to a reduction in the visual span.
This hypothesis predicts that reading time (msec/word) becomes increasingly dependent
on word length as text contrast decreases. We tested and confirmed this prediction
using the rapid serial visual presentation (RSVP) method. Estimates of the visual
span ranged from about 10 characters for high-contrast text to less than two characters
for low-contrast text. Eye-movement recordings showed that longer reading times at
low contrast are partitioned about equally between prolonged fixation times and an
increased number of saccades (presumably related to a reduced visual span). RSVP measurements
for six out of seven low-vision subjects revealed a strong dependence of reading time
on word length, as expected from reduced visual spans.