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Oren Yehezkel, Uri Polat; Meridional asymmetry of collinear interactions in the normal visual cortex. Journal of Vision 2008;8(6):796. doi: 10.1167/8.6.796.
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© ARVO (1962-2015); The Authors (2016-present)
Maturation of neural connectivity is experience-dependent in such a way that the state of the visual input during the critical period can be inferred from the visual functions in adults. In meridional amblyopia, the visual input during the critical period was asymmetrical; hence, the perception in one meridian was blurred, but normal in the orthogonal one. Consequently, in adults, the contrast sensitivity and the lateral interactions (LI) are dramatically reduced along the blurred meridian, but practically normal along the orthogonal one. However, asymmetric visual input is common during normal development and young children tend to be astigmatic (with the vertical meridian being more blurred than the horizontal). This effect decreases and usually disappears with increasing age. Here we explored whether this visual asymmetry during the critical period shaped the development of the visual connectivity and induced a cortical asymmetry that was retained during adulthood in adults with normal vision. Subjects had corrected vision of 6/6 or better. Contrast sensitivity to Gabor patch and collinear facilitation were measured under monocular and binocular conditions using dichoptic glasses. We found significant differences in the LI between the horizontal and the vertical meridians which are not due to different detection thresholds of the target. Monocular LI along the horizontal meridian are higher by 58% than the vertical. In contrast, binocular LI along the vertical meridian are higher by 35% than the horizontal. We suggest that the vertical blur induced by the optical astigmatism during the “critical period” prevents the development of normal monocular LI along the vertical meridian. The decreased binocular summation in the horizontal meridian is probably caused by developmental alternations in the superposition of the corresponding points between the eyes. Alternatively, the reduced binocular facilitation along the horizontal meridian could result from higher inter-ocular suppression along this meridian.
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