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DJ Stackhouse, J Shallo-Hoffmann, C Woodruf; Fixation Duration during Reading of Horizontal and Vertical Number Series . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4664.
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Purpose:To investigate fixation duration of a monosyllabic number during a reading task of horizontal and vertical number series. Methods: Twenty young (20-33yr, mean: 25.7yr), healthy adults who had English as their mother tongue and normal corrected visual acuity underwent binocular eye movement recordings (miniature video cameras; 250 images/sec) to document horizontal and vertical eye movements (sampling rate: 250 Hz, resolution, 0.01º) and head position, during a reading task. Subjects fixated a computer-generated series of horizontally or vertically presented number arrays, located at a distance of 100 cm. The subject's task was to read a series of numbers under one of the following randomly presented conditions: a number series read from left to right; right to left; top to bottom; and bottom to top. Each condition was presented only once. Data analysis started with the fourth and ended with the third from last numerical digit of the series. Visual acuity, attention, fatigue, language experience, and number of syllables in the spoken word were controlled. Fixation duration (in msec) for each numerical digit was measured. The entire experiment took 20 minutes to perform, including calibration. Results:The mean fixation duration on a monosyllabic number was as follows for the four reading directions: left-to-right - 276.5 +/- 43.1 msec; right-to-left - 267.4 +/-51.6 msec; top-to-bottom - 318.1 +/- 45.8 msec; and bottom-to-top - 316.1+/-45.8 msec. Fixation duration increased in both directions during vertical reading as compared to both directions during horizontal reading (ANOVA : F= 24.8, df-3;p<0001; sphericity assumed). Conclusion:Fixation duration increased when reading involved eye movements orthogonal to familiar reading directions for Native-English speaking adults. An accurate description of base-line characteristics of normal fixation duration is useful to detect dysfunction.
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