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Lore Thaler, James T. Todd, Delwin T. Lindsey; Phase dependent local energy mediates effects of phase scrambling on shape perception from texture. Journal of Vision 2005;5(8):994. doi: 10.1167/5.8.994.
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© ARVO (1962-2015); The Authors (2016-present)
Models of 3D shape perception from texture often consider local Fourier amplitude spectrum of an image but ignore the phase spectrum. Last VSS we reported that phase scrambling impairs shape perception for blob but not contour textures. The present study was designed to investigate why phase scrambling affects shape perception for some textures but not for others. We used five texture patterns [random polka dots (dots), dots organized in horizontal-vertical (dotgrid) or diagonal (dots45) directions, and lines organized in horizontal-vertical (grid) or horizontal-vertical-diagonal (grid90-45) directions] and their phase-scrambled counterparts. Observers viewed 20 degree optical projections of ellipsoidal cylinders homogeneously textured with each of our 10 textures, and judged the apparent cross-section in depth of each surface by adjusting the shape of an elliptical arc presented on a separate monitor. Observers' depth perception decreased with phase scrambling for ‘dots’ and ‘grid90-45’, but remained unchanged for ‘dotgrid’, ‘dots45’ and ‘grid’.
To further examine influence of phase scrambling on shape from texture, we calculated phase dependent local energy (Morrone & Burr, 1988) for images of various surface patches differing in slant. Local energy was computed as the sum of weighted responses of a bank of 5 spatial × 6 orientation-tuned quadrature pairs of filters (Kovesi, 1999). The subsequent comparison of filter responses between unscrambled and scrambled texture patterns revealed high correlations of filter responses for cases where 3-D shape perception was hardly affected by phase scrambling (r2 > .91). On the other hand, correlations of filter responses were much lower when shape perception was reduced by phase scrambling (r2 < .56). Local amplitude spectra did not differentiate between ‘good’ and ‘bad’ scrambled textures. The results suggest that mechanisms underlying 3D shape from texture are sensitive to both amplitude and phase of local Fourier spectra.
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