AMBLYOPIC QUASI-BLINDNESS FOR IMAGE STRUCTURE

Human amblyopes display reduced contrast sensitivities, suffer from pe rceptual distortion, and their letter acuities are worse than is predi cted from grating visibility. We sought the origin of these dysfunctio ns by measuring normal and amblyopic sensitivities to various forms of well-defined image distortion, namely band-limited phase quantization , phase quantization with additional amplitude modulation, and grey-sc ale modification. Our results prove the existence of an amblyopic quas i-blindness to image structure, that cannot be explained in terms of c ontrast detection. We discuss these findings within the computational scheme of image decomposition into local amplitude and local phase val ues. They are consistent with the assumption of amblyopic eyes being i mpaired in processing local phase but having the local amplitude (or ' 'energy'', possibly at reduced gain) at their disposal. Phrased in phy siological terms, we propose a scheme of complex-cells-only vision in amblyopia. We also provide a demonstration of how amblyopic eyes may s ee the test stimuli and natural images by generating local amplitude a nd phase representations at limited phase resolution. Copyright (C) 19 96 Elsevier Science Ltd.