Abstract
The visual deficit in amblyopia involves both elevated contrast thresholds and distorted suprathreshold percepts at high spatial frequencies. It is currently unclear whether these two anomalies are part of the same neural disturbance or whether they reflect different neural dysfunction. The quality of the spatial percepts in amblyopia was assessed at detection threshold. The ability of amblyopes to discriminate the orientation and local spatial phase of well-localized spatial stimuli was measured at the detection threshold. Measurements were made as a function of spatial frequency. Performance seemed normal for orientation discrimination, even at high spatial frequencies, but, in some cases, it was disturbed in phase discrimination. A different explanation and neural basis is needed to encompass both threshold and suprathreshold spatial deficits in amblyopia.
Highlights
The visual deficit in amblyopia involves both elevated contrast thresholds and distorted suprathreshold percepts at high spatial frequencies
Performance seemed normal for orientation discrimination, even at high spatial frequencies, but, in some cases, it was disturbed in phase discrimination
Amblyopia is a uniocular impairment of vision resulting from strabismus, anisometropia, or form deprivation occurring early in visual development
Summary
The quality of the spatial percepts in amblyopia was assessed at detection threshold. The ability of amblyopes to discriminate the orientation and local spatial phase of welllocalized spatial stimuli was measured at the detection threshold. Measurements were made as a function of spatial frequency. All stimuli were generated and presented and the response collected and analyzed on a minicomputer The stimuli were presented in a Joyce Electronics video monitor (raster display; 30 cm ϫ 20 cm with a white P4 phosphor; Cambridge, Cambridge, UK) through an interface (Design CED 502; Cambridge Electronics). The contrast linearity of the display screen was measured and found to hold up to 98% contrast. Oriented sinusoidal grating patterns, in which contrast was modulated sinusoidally in time were used to measure thresholds for contrast detection. The choice of the horizontal orientation ensured that any unsteadiness of the eye (predominantly in the horizontal plane) would not interfere with measurement accuracy by introducing retinal image smear.[21]
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