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Frank A Proudlock, Esha Prakash, Sarah White, Kevin Paterson, Irene Gottlob, Rebecca McLean; Word Reading in Infantile Nystagmus. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4416.
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© ARVO (1962-2015); The Authors (2016-present)
Infantile nystagmus (IN) impairs global measures of reading such as maximum reading speed, however, the effect of IN on local eye movement control during reading is unclear. In normal readers, precise and immediate control of eye movements occurs with online adjustments of the duration and number of fixations on words as a function of their visual (e.g. word length) and lexical (e.g. word frequency) characteristics. Normal readers also tend to fixate at the preferred viewing position, just left of word centre, especially for longer words. We examined whether visual (word length) and lexical (word frequency) factors also modulate local eye movement control in individuals with IN.
Eye movements of participants were recorded from 31 IN participants (12 idiopathic IN, 16 albinism; 3 congenital stationary night blindness) and 15 controls whilst reading sentences containing target words modified according to: (i) word length (40 sentences), and (ii) word frequency (80 sentences). A three-stage active calibration method was repeated throughout the task to ensure spatial accuracy of the recordings. For target words, measures included: (a) first fixation (in controls) or foveation (in IN) duration (FFD), (b) number of the first pass foveations or fixations (FPF), and (c) gaze duration (sum duration of all FPF). Relative landing sites of foveations in long and short target words were also examined.
Word length and word frequency effects were evident in both IN and control participants who made greater gaze durations on longer (p<0.001) and low frequency (p=0.001) target words. For IN participants, these were achieved by increasing the number of FPF (p=0.001) but not FFD (p>0.4). In contrast, controls increased both number of FPF (p<0.01) and FFD (p<0.001). Individuals with idiopathic IN were able to locate foveations towards the beginning of longer words, similar to controls (p<0.01). This effect was not observed in albinism.
Individuals with IN demonstrate local control of eye movements during word reading modulating gaze durations on words in relation to their visual or lexical content. This is achieved by making on-line changes to the number of foveations but not their duration. Individuals with idiopathic IN are better able to locate foveations at the preferred viewing position, towards the beginning of longer target words, compared to those with albinism, presumably because of better foveal vision.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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