Psychophysics of reading XX. Linking letter recognition to reading speed in central and peripheral vision

Our goal is to link spatial and temporal properties of letter recognition t o reading speed for text viewed centrally or in peripheral vision. We propo se that the size of the visual span - the number of letters recognizable in a glance - imposes a fundamental limit on reading speed, and that shrinkag e of the visual span in peripheral Vision accounts for slower peripheral re ading. In Experiment 1, we estimated the size of the visual span in the low er visual field by measuring RSVP (rapid serial visual presentation) readin g times as a function of word length. The size of the visual span decreased from at least 10 letters in central vision to 1.7 letters at 15 degrees ec centricity, in good agreement with the corresponding reduction of reading s peed measured by Chung and coworkers (Chung, S. T. L., Mansfield, J. S., & Legge, G. E. (1998). Psychophysics of reading. XVIII. The effect of print s ize on reading speed in normal peripheral vision. Vision Research, 38, 2949 -2962). In Exp. 2, we measured letter recognition for trigrams (random stri ngs of three letters) as a function of their position on horizontal lines p assing through fixation (central vision) or displaced downward into the low er Visual field (5, 10 and 20 degrees). We also varied trigram presentation time. We used these data to construct visual-span profiles of letter accur acy versus letter position. These profiles were used as input to a paramete r-free model whose output was RSVP reading speed. A version of this model c ontaining a simple lexical-matching rule accounted for RSVP reading speed i n central vision. Failure of this version of the model in peripheral vision indicated that people rely more on lexical inference to support peripheral reading. We conclude that spatiotemporal characteristics of the visual spa n limit RSVP reading speed in central vision, and that shrinkage of the vis ual span results in slower reading in peripheral vision. (C) 2001 Elsevier Science Ltd. All rights reserved.