PSYCHOPHYSICS OF READING - XVIII - THE EFFECT OF PRINT SIZE ON READING SPEED IN NORMAL PERIPHERAL-VISION

Reading in peripheral vision is slow and requires large print, posing substantial difficulty for patients with central scotomata. The purpos e of this study was to evaluate the effect of print size on reading sp eed at different eccentricities in normal peripheral vision. We hypoth esized that reading speeds should remain invariant with eccentricity, as long as the print is appropriately scaled in size-the scaling hypot hesis. The scaling hypothesis predicts that log-log plots of reading s peed versus pl int size exhibit the same shape at all eccentricities, but shift along the print-size axis. Six normal observers read aloud s ingle sentences(similar to Il words in length) presented on a computer monitor, one word at a time, using rapid serial visual presentation ( RSVP). We measured reading speeds (based on RSVP exposure durations yi elding 80% correct) for eight print sizes at each of six retinal eccen tricities, from 0 (foveal) to 20 deg in the inferior visual held. Cons istent with the scaling hypothesis, plots of reading speed versus prin t size had the same shape at different eccentricities: reading speed i ncreased with print size, up to a critical print size and was then con stant at a maximum reading speed for larger print sizes. Also consiste nt with the scaling hypothesis, the plots shifted horizontally such th at average values of the critical print size increased from 0.16 deg ( fovea) to 2.22 deg (20 deg peripheral). Inconsistent with the scaling hypothesis, the plots also exhibited vertical shifts so that average v alues of the maximum reading speed decreased from 807 w.p.m. (fovea) t o 135 w.p.m. (20 deg peripheral). Because the maximum reading speed is not invariant with eccentricity even when the print size was scaled, we reject the scaling hypothesis and conclude that print size is not t he only factor limiting maximum reading speed in normal peripheral vis ion. (C) 1998 Elsevier Science Ltd. All rights reserved.