Aliased Frequencies Enable the Discrimination of Compound Gratings in Peripheral Vision

Although gratings beyond the Nyquist limit of the peripheral retina are visible as aliased percepts when presented in isolation, the reported lack of aliasing for targets with complex spectra (edges, lines, letters) suggests that aliased frequency components are invisible in the presence of sub-Nyquist image components. We tested this hypothesis by systematically exploring a range of stimulus parameters in search of conditions which would enable subjects to detect the supra-Nyquist components of a compound grating. A three-alternative forced-choice masking paradigm was used, which required subjects to discriminate a 2.5 deg patch of compound grating (mask + test) from a simple grating (mask only). Using a 2 c/deg grating as the masking component, which is well below the 4 c/deg Nyquist limit to veridical perception at 20 deg in the horizontal nasal field, we varied the spatial frequency of the test grating over a range extending above and below the Nyquist frequency. We found that aliased, supra-Nyquist components are reliably detected in the presence of high contrast, sub-Nyquist gratings, provided they have sufficient contrast. Contrast threshold for detecting the aliased gratings was higher when presented as a component of the compound grating than when presented in isolation. This masking effect of the sub-Nyquist component was not specific to supra-Nyquist test targets, however, since a similar masking effect also occurred for sub-Nyquist targets. These results suggest that the invisibility of aliasing described previously for edges or square wave gratings is due primarily to the combination of the low amplitudes of supra-Nyquist harmonics in such stimuli and a high contrast threshold of the peripheral retina. The additional masking effects of the sub-Nyquist, fundamental component of a square wave on the supra-Nyquist harmonics make the detection of aliasing impossible even for very high contrast square wave gratings presented in the periphery.

[1]  R. Hess,et al.  Human peripheral spatial resolution for achromatic and chromatic stimuli: limits imposed by optical and retinal factors. , 1991, The Journal of physiology.

[2]  C.E. Shannon,et al.  Communication in the Presence of Noise , 1949, Proceedings of the IRE.

[3]  D. Macleod,et al.  Local luminance nonlinearity and receptor aliasing in the detection of high-frequency gratings. , 1996, Journal of the Optical Society of America. A, Optics, image science, and vision.

[4]  David Williams,et al.  No aliasing at edges in normal viewing , 1992, Vision Research.

[5]  D J Field,et al.  Relations between the statistics of natural images and the response properties of cortical cells. , 1987, Journal of the Optical Society of America. A, Optics and image science.

[6]  D. Williams,et al.  Cone spacing and the visual resolution limit. , 1987, Journal of the Optical Society of America. A, Optics and image science.

[7]  L. Thibos,et al.  Retinal limits to the detection and resolution of gratings. , 1987, Journal of the Optical Society of America. A, Optics and image science.

[8]  J. M. Foley,et al.  Contrast masking in human vision. , 1980, Journal of the Optical Society of America.

[9]  D. G. Green,et al.  Optical and retinal factors affecting visual resolution. , 1965, The Journal of physiology.

[10]  Larry N. Thibos,et al.  Undersampling produces non-veridical motion perception, but not necessarily motion reversal, in peripheral vision , 1996, Vision Research.

[11]  David Williams.  Aliasing in human foveal vision , 1985, Vision Research.

[12]  A Bradley,et al.  New methods for discriminating neural and optical losses of vision. , 1993, Optometry and vision science : official publication of the American Academy of Optometry.

[13]  H. Wilson,et al.  Spatial frequency tuning of orientation selective units estimated by oblique masking , 1983, Vision Research.

[14]  G E Legge,et al.  Contrast discrimination in peripheral vision. , 1987, Journal of the Optical Society of America. A, Optics and image science.

[15]  Stephen J. Anderson,et al.  Post-receptoral undersampling in normal human peripheral vision , 1990, Vision Research.

[16]  R A Smith,et al.  Aliasing in the parafovea with incoherent light. , 1987, Journal of the Optical Society of America. A, Optics and image science.

[17]  A. Hendrickson,et al.  Human photoreceptor topography , 1990, The Journal of comparative neurology.

[18]  N J Coletta,et al.  Psychophysical estimate of extrafoveal cone spacing. , 1987, Journal of the Optical Society of America. A, Optics and image science.

[19]  Dan J. Swift,et al.  Spatial frequency masking and Weber's Law , 1983, Vision Research.

[20]  C. A. Burbeck,et al.  Contrast gain measurements and the transient/sustained. , 1981, Journal of the Optical Society of America.

[21]  David R. Williams,et al.  Off-axis optical quality and retinal sampling in the human eye , 1996, Vision Research.

[22]  Jeffrey A. Sloan,et al.  Spatial frequency analysis of the visual environment: Anisotropy and the carpentered environment hypothesis , 1978, Vision Research.

[23]  W. Weibull.  A Statistical Distribution Function of Wide Applicability , 1951 .

[24]  N. Drasdo,et al.  Parvocellular neurons limit motion acuity in human peripheral vision , 1995, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[25]  J. M. Foley,et al.  Human luminance pattern-vision mechanisms: masking experiments require a new model. , 1994, Journal of the Optical Society of America. A, Optics, image science, and vision.

[26]  C. Curcio,et al.  Topography of ganglion cells in human retina , 1990, The Journal of comparative neurology.

[27]  J. Yellott.  Spectral analysis of spatial sampling by photoreceptors: Topological disorder prevents aliasing , 1982, Vision Research.

[28]  Hugh R. Wilson,et al.  Eccentricity dependence of contrast matching and oblique masking , 1985, Vision Research.

[29]  F. Campbell,et al.  Orientational selectivity of the human visual system , 1966, The Journal of physiology.

[30]  Yi-Zhong Wang.  Filtering, Sampling and Aliasing in Peripheral Vision. , 1996 .

[31]  Nancy J. Coletta,et al.  An oblique effect in parafoveal motion perception , 1993, Vision Research.

[32]  A. Bradley,et al.  Characterization of spatial aliasing and contrast sensitivity in peripheral vision , 1996, Vision Research.

[33]  A Bradley,et al.  Contrast dependence and mechanisms of masking interactions among chromatic and luminance gratings. , 1988, Journal of the Optical Society of America. A, Optics and image science.

[34]  L N Thibos,et al.  Effect of window size on detection acuity and resolution acuity for sinusoidal gratings in central and peripheral vision. , 1996, Journal of the Optical Society of America. A, Optics, image science, and vision.

[35]  Jacob Nachmias,et al.  On the psychometric function for contrast detection , 1981, Vision Research.

[36]  L. N. Thibos,et al.  Vision beyond the resolution limit: Aliasing in the periphery , 1987, Vision Research.

[37]  H. Wilson,et al.  Orientation bandwidths of spatial mechanisms measured by masking. , 1984, Journal of the Optical Society of America. A, Optics and image science.

[38]  I. Ohzawa,et al.  A comparison of contrast detection and discrimination , 1986, Vision Research.

[39]  A. Derrington,et al.  Refraction, aliasing, and the absence of motion reversals in peripheral vision , 1995, Vision Research.

[40]  David R. Williams,et al.  Consequences of spatial sampling for human motion perception , 1990, Vision Research.