Higher order image structure enables boundary segmentation in the absence of luminance or contrast cues

Lower order image statistics, which can be described by an image's Fourier energy content, enable segmentation when they are different on either side of a boundary. We have previously demonstrated that the spatial distribution of the energy in an image (described by its higher order statistics or structure) could influence segmentation thresholds for contrast- and orientation-defined boundaries, even though it was the same on either side of the boundary and thus task irrelevant (Zavitz & Baker, 2013). Here we examined whether higher order statistics can also enable segmentation when boundaries are defined by differences in structure or density of texture elements. We used micropattern-based naturalistic synthetic textures to manipulate the sparseness, global phase alignment, and local phase alignment of carrier textures and measured segmentation thresholds based on forced-choice judgments of boundary orientation. We found that both global phase structure and sparseness, but not local phase alignment, enable segmentation and that local structure also has a small effect on segmentation thresholds in both cases. Simulations of a two-stage filter model with a compressive intermediate nonlinearity can reproduce the major features of the experimental data, segmenting boundaries defined by higher order statistics alone while capturing the influence of global image structure on segmentation thresholds.