September 2011
Volume 11, Issue 11
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2011
The word length effect in virtual hemianopia, real hemianopia, and alexia
Author Affiliations
  • Claire Sheldon
    Department of Ophthalmology and Visual Sciences, University of British Columbia
  • Mathias Abegg
    Department of Ophthalmology, University of Bern
  • Alla Sekunova
    Department of Ophthalmology and Visual Sciences, University of British Columbia
    Department of Medicine (Neurology), University of British Columbia
  • Jason Barton
    Department of Ophthalmology and Visual Sciences, University of British Columbia
    Department of Medicine (Neurology), University of British Columbia
    Department of Psychology, University of British Columbia
Journal of Vision September 2011, Vol.11, 859. doi:10.1167/11.11.859
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      Claire Sheldon, Mathias Abegg, Alla Sekunova, Jason Barton; The word length effect in virtual hemianopia, real hemianopia, and alexia. Journal of Vision 2011;11(11):859. doi: 10.1167/11.11.859.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Background: A characteristic feature of pure alexia is the word-length effect, in which reading speed increases with increasing word length. However, many alexic patients also have right hemianopia, which can itself can cause a hemianopic dyslexia. The degree to which hemianopia causes a word-length effect is therefore an important question. Objective: Our goal was to determine if a word-length effect could be generated under hemianopic conditions in the absence of damage to language processing areas. Method: 13 healthy adults read single words of 3 to 9 letters in length while eye movements were monitored with full-field viewing and then with gaze-contingent displays simulating right or left hemianopia. We also studied 6 patients with reading problems: two had hemianopic dyslexia without fusiform lesions, four had fusiform lesions causing alexia, two of which had associated hemianopia while two had full visual fields. Results: In healthy subjects, there was a small word-length effect with full-field viewing of 14ms/letter, which more than doubled to 37 ms/letter for right and 31ms/letter for left hemianopia. The upper 95% prediction limit was 51 ms/letter for full-field viewing and 160 ms/letter for right hemianopia. These results were corroborated by our patient sample. Our two patients with hemianopic dyslexia fell within the virtual hemianopic range (18.9, 95.1 ms/letter), while the two patients with fusiform lesions causing alexia and hemianopia had word-length effects well beyond this range (1536, 16500 ms/letter). The subjects with alexia without hemianopia had modest word-length effects that were abnormal compared to full-field viewing (53, 182 ms/letter). Conclusions: Hemianopic simulations show a small word-length effect of up to 160 ms/letter. Given that word-length effects of similar magnitude can be seen in alexia without hemianopia, in patients with hemifield loss in the central 5°, word-length effects should be larger before concluding that there is an additional component of alexia.

MA was supported by a grant from the Swiss National Science Foundation. 
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