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Y.–Z. Wang, C.E. Wilson, J. Felius, E.E. Birch; The Roles of Position and Orientation Features in Shape Discrimination Deficits of Amblyopia . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5407.
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© ARVO (1962-2015); The Authors (2016-present)
While it is well documented that positional deficit is a defining characteristic of human amblyopia, it is unclear if this positional uncertainty is secondary to other types of spatial deficits, such as abnormal orientation coding, as recently suggested. In this study, we examined the independent roles of local position and orientation features in shape discrimination deficits of amblyopia.
Twenty–two normal children (age 8 to 17 years) and 7 amblyopic children (age 8 to 14 years, visual acuity of the affected eye ranging from 20/32 to 20/160) participated in the study. Stimuli were continuous radial frequency (RF) patterns and Gabor patch sampled RF patterns. Gabor patches were placed either at the peaks and troughs of sinusoidal radial modulation (position patterns, only having patch location change with modulation) or at the zero–crossings of the modulation (orientation patterns, only having patch orientation change with modulation). The carrier spatial frequency was 3 cpd; radial frequency was 4 cycles; mean radius was 1.6 deg; contrast was 100%; size of the Gabor patches was half the carrier wavelength. A temporal 2AFC staircase paradigm was employed to determine the modulation thresholds.
When detecting continuous RF patterns, the affected eyes of amblyopes had a mean+/–SD modulation threshold of 1.17%+/–0.57%, which was significantly higher than that of the fellow eyes (0.48%+/–0.15%, p<0.01) or that of normal eyes (0.42%+/–0.12%, p<0.001). For Gabor patch sampled RF patterns, the average modulation threshold obtained from the affected eyes for detecting position patterns (3.66%+/–2.0%) was higher than that obtained from the fellow eyes (2.23%+/–0.72%, p=0.18) or the normal eyes (2.39%+/–0.73%, p<0.025). In contrast, the affected eyes' threshold for detecting orientation patterns (1.63%+/–0.74%) was not significantly different from that of the fellow eyes (1.59%+/–0.34%, p=0.92) or the normal eyes (1.87%+/–0.90%, p=0.62). There was no significant difference in performance between the fellow eyes and the normal eyes.
Affected eyes showed deficits for detecting continuous RF patterns with thresholds similar to those for detecting orientation changes, while thresholds for detecting position changes were vastly elevated. These results provide strong evidence to support the hypothesis that abnormal positional coding, rather than abnormal orientation coding, is the neural mechanism that may underlie spatial vision deficits in amblyopia.
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