Psychophysics of reading—XVI. The visual span in normal and low vision

• Published in: Vision research (Oxford) Vol. 37; no. 14; pp. 1999 - 2010
• Main Authors: Legge, Gordon E., Ahn, Sonia J., Klitz, Timothy S., Luebker, Andrew
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.07.1997; Elsevier Science
• Subjects: Adolescent; Adult; Biological and medical sciences; Contrast; Contrast Sensitivity; Eye Movements; Female; Fixation, Ocular; Humans; Low vision; Male; Medical sciences; Ophthalmology; Psychophysics; Reading; Saccades; Time Factors; Vision disorders; Vision, Low - physiopathology; Visual span; Visual span; Reading; Low vision; Eye movements; Contrast; Human; Visual fixation; Vision disorder; Word length; Duration; Text; Eye movement; Language; Vision; Perception
• ISSN: 0042-6989; 1878-5646
• DOI: 10.1016/S0042-6989(97)00017-5

The visual span in reading is the number of characters that can be recognized at a glance. The shrinking visual span hypothesis attributes reading speed 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.