READING WITH ECCENTRIC FIXATION: COMPARISON OF NORMAL AND LOW VISION

Gary Rubin

Abstract

Individuals with central scotomas usually read much more slowly than visually-impaired people without central scotomas. In a previous study we determined that inefficient eye movements could account for only part of this deficit. By presenting text sequentially, one word at a time in the same location in the visual field (Rapid Serial Visual Presentation or RSVP) we were able to minimize the need for saccadic eye movements which limit reading speed. However even with RSVP central-scotoma subjects read slower than subjects with intact central fields. In this study we examine the extent to which this deficit reflects processing limitations inherent to peripheral vision. RSVP reading rates for central- scotoma subjects were compared to RSVP reading rates of normal subjects using peripheral vision. Peripheral reading rates were measured with voluntarily maintained fixation and with text stabilized at known retinal eccentricities by means of a dual purkinje-image eyetracker. In both cases, the size of the text was scaled to compensate for reduced resolution in the periphery. Under stabilized conditions reading rate dropped exponentially with eccentricity from 1300 words/min at the fovea to 52 words/min at 10 degrees. With voluntary fixation reading rate dropped less rapidly at eccentricities greater that 2.5 degrees (down to 80 words/min at 10 degrees). Low-vision subjects voluntarily maintained fixation at their preferred eccentricity. We determined the eccentric fixation locus by recording eye movement patterns with a scanning laser ophthalmoscope during simulated reading trials. Subjects with long- standing central scotomas read considerably slower (by a factor of 1.6 or more) than normal subjects using the same retinal eccentricity. This suggests that limitations inherent to normal peripheral vision do not fully account for the slow RSVP reading speeds of low-vision subjects with central scotomas.

Details

Year: 1992

Program Number: 2:00 pm

Author Affiliation: n/a

Co-Authors: Kathleen Turano

Co-Author Affiliation: n/a

Room: Scotland B