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Alexandre Reynaud, Robert F Hess; An unexpected spontaneous Pulfrich phenomenon in amblyopia. Journal of Vision 2019;19(10):223d. doi: https://doi.org/10.1167/19.10.223d.
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The binocular viewing of a fronto-parallel pendulum with a reduced luminance in one eye results in the illusory tridimensional percept of the pendulum following an elliptical orbit in depth, the so-called Pulfrich phenomenon (Pulfrich, 1922). A small percentage of mild anisometropic amblyopes who have rudimentary stereo are known to experience a spontaneous Pulfrich phenomenon, which posits a delay in the cortical processing of information involving their amblyopic eye. In order to characterize this posited delay, we used a paradigm where a cylinder rotating in depth, defined by moving Gabor patches at different disparities (i.e. at different interocular phases), generates a strong to ambiguous depth percept. This paradigm allows one to accurately measure a spontaneous Pulfrich effect (i.e. PSE≠0) and to determine how it depends on the spatio-temporal properties of stimulus. We observed a spontaneous Pulfrich phenomenon in amblyopia which has been posited to be due to an interocular delay associated with amblyopic processing. Surprisingly, the posited delay was not always associated with amblyopic processing, was not a consequence of the reduced contrast sensitivity of the amblyopic eye and displayed a large variability across amblyopic observers. Increasing the density, decreasing the spatial frequency or increasing the speed of the stimulus tend to reduce the posited delay. As previously observed in controls, this delay can also be reduced or increased by a monocular manipulation of the contrast or the luminance of the stimulus. The spontaneous Pulfrich phenomenon see by some amblyopes is variable and depends on the spatio-temporal properties of the stimulus which complicates any explanation in terms of a fixed processing delay.
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