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A. F. Macedo, M. D. Crossland, G. S. Rubin; The Role of Fixation Stability When Reading With the Peripheral Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2532.
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© ARVO (1962-2015); The Authors (2016-present)
People with central scotoma rely on their peripheral retina to read. The use of peripheral retina increases fixation instability which can be a limiting factor for reading. In this study we investigated the effect of fixation instability on reading speed of people with simulated central scotomas.
Reading speed of five normally sighted observers was measured 5º above and below the fovea. Sentences were presented using a rapid serial visual presentation (RSVP) paradigm and an eyetracker (Eyelink I, SMI) was used to change presentation conditions. In the baseline condition, a fixation target was visible and words were static. In all other conditions words were presented under gaze-contingent conditions, where eye movements were modulated by a gain factor (gain = word velocity/eye velocity) to change the stability of the words during fixations. Gain 1 corresponds to words presented stabilized in the retina and gain 10 corresponds to words presented with increased retinal instability. Reading speed was measured under both gain conditions with and without allowing intra-saccades within words. Data were normalized using the baseline reading speed and analyzed using linear mixed models.
Where within-word saccades were not permitted, gain 1 increased reading speed compared to baseline (mean increase = 38.5%, p = 0.004) and gain 10 reduced reading speed compared to gain 1 (mean reduction = 48.6%, p < 0.001). When within-word saccades were allowed, gain 10 produced slower reading speed than gain 1 (mean reduction = 51.5%, p = 0.02). Reading speed for all other conditions was not significantly different from baseline. Reading speeds were equal under each gain condition with and without intra-word saccades.
Stabilized text presented under gaze-contingent conditions was read faster than static (non gaze-contingent) text or text presented with increased instability. Reading under gaze-contingent conditions might be faster because attention was not divided between a fixation target and the word. Increased instability is likely to increase crowding and reduce the visibility of words. There was no advantage of within-word saccades, perhaps because the exposure time of the words was below the latency of voluntary saccades. Our results indicate that fixation instability might be a limiting factor for reading with peripheral retina.
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