Abstract
Cross-orientation suppression (COS) in striate cortex has been implicated in the efficient encoding of visual stimuli. We show that release from COS facilitates the decoding of 3-D shape. In planar surfaces overlaid with textures, slanting the surface can increase the visibility of the component parallel to the slant. Since this component provides the orientation flows that signify 3-D shape, the enhancement of visibility facilitates 3-D slant perception. Contrast thresholds reveal that this enhancement results from a decrease in COS when 3-D slant creates a frequency mismatch between texture components. We show that coupling compressive nonlinearities in LGN neurons with expansive nonlinearities in cortical neurons can model the frequency-specific component of suppression.
Highlights
In the perspective image of a slanted textured surface, oriented components of the texture that are aligned with the 3-D slant converge to form orientation flows ([1,2,3]), while components orthogonal to the slant increase in frequency (Figure 1a)
We have previously shown that perceived orientation flows determine the perception of 3-D shape from texture ([3,5,19,20]). 3-D shape is not perceived when the flows are physically present if they are masked by other components
Several electrophysiological studies examining the frequency selectivity of Cross-orientation suppression (COS) suggest that suppression mechanisms are broadly tuned ([11,25,26]), it is unclear whether this kind of tuning plays out psychophysically. It would be remarkable if the facilitation of 3-D shape perception occurs automatically through the neural processes that lead to COS, so to ascertain its locus, we have explored the possibility of frequency selectivity in an LGN based model
Summary
In the perspective image of a slanted textured surface, oriented components of the texture that are aligned with the 3-D slant converge to form orientation flows ([1,2,3]), while components orthogonal to the slant increase in frequency (Figure 1a). The increase in saliency is more pronounced in complex texture patterns, e.g. the octotropic plaid, which consists of eight gratings of the same frequency, spaced in orientation (Figure 1a bottom). Since these converging orientation flows play a critical role in conveying the perceived 3-D slant and shape of the surface ([3,4,5,6]), an increase in their saliency should enhance the 3-D perceived slant. If different oriented components were processed independently by the visual system, the increase in saliency of the components parallel to the slant could be due just to the reduced visibility of the other components. Independent processing of different orientations is not a feasible premise
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