Abstract
In images of textured three-dimensional surfaces, pattern changes can be characterized as changes in orientation and spatial frequency, features for which neurons in primary visual cortex are classically selective. Previously, we have demonstrated that correct 3-D shape perception is contingent on the visibility of orientation flows that run parallel to the surface curvature. We sought to determine the relative contributions of orientation modulations (OMs) and frequency modulations (FMs) for the detection of slant and shape from 3-D surfaces. Results show that 1) when OM and FM indicate inconsistent degrees of surface slant or curvature, observer responses were consistent with the slant or curvature specified by OM even if the FM indicated a slant or curvature in the opposite direction to the same degree. 2) For slanted surfaces, OM information dictates slant perception at both shallow and steep slants while FM information is effective only for steep slants. Together these results point to a dominant role of OM information in the perception of 3-D slant and shape.
Highlights
The visual system is well able to extract information about 3dimensional (3-D) shape from monocular cues
For the inconsistent slanted condition, the percentage of trials reported consistent with the pattern (OM or Frequency modulations (FMs)) at a fixed base slant of 630 deg was plotted vs. the range of slants specified by the other pattern (Figure 3A and 3B)
When the slant specified by the Orientation modulations (OMs) was fixed at 630 deg, responses for the direction of slant were consistent with the OMs, even if the FMs specified a slant of the opposite sign to the same degree (Figure 3A)
Summary
The visual system is well able to extract information about 3dimensional (3-D) shape from monocular cues. One potentially powerful monocular cue is the pattern or texture on a surface, which when projected in perspective, results in systematic changes in the texture in the image. These changes have commonly been referred to as texture gradients (e.g. size, density, compression) [1], and their abilities to convey 3-D shape have been studied extensively in the literature [2,3,4,5,6,7]. Many gradient-based shape-from-texture models contain an assumption of homogeneity and use deviations from homogeneity to extract 3-D shape [8,9,10,11], not all surface textures are homogeneous. Orientation flows play a critical role in 3-D shape perception in textured surfaces [23,24] and in specular and shaded surfaces [25,26,27], and provide a generic source of information for neural models of 3-D shape
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