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S. Naito, S. Kikuchi, Y. Hirano; Is the Vertical–horizontal Anisotropy Caused by Stereotuned Cells? . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5685.
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Along the vertical median line, the oculardominancecolumns in V1 and the stripes in V2 align horizontally perpendicularto the median line. The alignment coincides with the stereopsisepipolar line. Is there any anisotropy of visual acuities dueto the stereotuned cells arrangement? We speculate that in someconditions the horizontal(H) spatial frequency perception acuitymight be more accurate than that of the vertical(V).
Three subjects, normal in vision without astigmatism,observed gratings in a flash display. Each of the four differentstimuli had 2 gratings. In the following example, the gratingwas on the top right quarter of the screen, the other was onthe bottom left. The gratings are composed of several line segmentswith the interval of 1.5 degree visual angle. The interval inone of the two gratings was slightly widened. In the other 3variations, the gratings were positioned in the opposite sidesof the diagram, and had differing line interval widths. Thewidth differences are shown in the table. Subjects were askedfor a forced–choice to tell which of the 2 gratings iswider.
In the 6.2% width difference conditions, the maximumanisotropy was obtained, at which the correct responses forV and H were fairly above and below 75%. In the easier caseof 10.0% difference, the rates are both high. The 3.3% case,the performance was close to the chance level. The data is theaverage of 120 tries by 3 subjects.
The H acuity was higher than the V. Although thecontributions from optic astigmatism were not ruled out completely,one of the possible origins of the V–H anisotropy mightbe the columns arrangements anisotropy in the V1 or the thickstripes in the V2, including stereotuned cells functions.
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