Interaction between sub- and supra-Nyquist spatial frequencies in peripheral vision.
In peripheral vision, high-frequency gratings beyond the Nyquist limit are visible as aliased patterns but, as shown previously, their visibility can be masked by superimposed sub-Nyquist gratings. Is the converse also true? Can supra-Nyquist gratings affect the detectability of sub-Nyquist gratings? In this study, we investigated the masking effect of high contrast, supra-Nyquist components of a compound grating on the contrast detection of sub-Nyquist components by employing a temporal three-alternative, forced-choice (3AFC) masking paradigm. We found that high-frequency, aliased gratings with contrast just 2 or 3 times above threshold can have a powerful masking effect on low-frequency, resolved gratings in peripheral vision. This result was surprising because prior results from sub-Nyquist masking studies in the fovea and the periphery have indicated that masking occurs only when the mask contrast is at least 5 times greater than threshold. Strong masking by supra-Nyquist gratings that are only just visible may be accounted for by an irregular sampling model in which the alias of the mask is distributed over a band of frequencies in the sub-Nyquist range. Furthermore, if undersampling is the explanation for the results of this study, then masking must occur after spatial sampling.
Wang
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YZ
Visual Sciences Group, School of Optometry, Indiana University, Bloomington 47405, USA. yizwang@astra.vision.mcgill.ca
Bradley
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A
Thibos
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D015350:Contrast Sensitivity / Q000502:physiology; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010470:Perceptual Masking / Q000502:physiology; D011594:Psychometrics; D012684:Sensory Thresholds / Q000502:physiology; D013997:Time Factors; D014794:Visual Fields