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Cerebral Cortex Advance Access published online on September 8, 2005
Cerebral Cortex, doi:10.1093/cercor/bhj033
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© The Author 2005. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oupjournals.org

Article

Boundary Cue Invariance in Cortical Orientation Maps

Chang'an A. Zhan 1* and Curtis L. Baker Jr1

1 McGill Vision Research Unit, Department of Ophthalmology, McGill University, Montreal, QC, Canada H3A 1A1

* To whom correspondence should be addressed.
Chang'an A. Zhan, E-mail: changan.zhan{at}mcgill.ca


  Abstract

We effortlessly perceive oriented boundaries defined by either luminance changes (‘first-order’ cues) or texture variations (‘second-order’ cues). Many neurons in mammalian visual cortex show orientation preference to both types of boundaries, but it is uncertain how they contribute to perceptual orientation cue-invariance at the neuronal population level. Using optical imaging in cat A18, we observed highly similar orientation preference maps to first-order and a variety of second-order visual stimuli. Thus the neuronal representation of coarse-scale boundary orientation appears to be invariant to the characteristics (including local orientation) of the fine-scale textures by which those boundaries are defined. A common feature of second-order visual stimuli is that modulation shifts their Fourier energy for boundary orientation to the higher spatial frequencies of their constituent textures -- our results suggest a common neural mechanism (demodulation) mediating visual processing of many kinds of texture boundary. The similarity between orientation maps to different stimuli implies that second-order responsive neurons are homogeneously distributed across the cortical surface. Such homogeneously cue-invariant orientation representation could provide a neural substrate for perceptual form-cue invariance, and reflect an optimal organization for encoding orientation information in natural scenes.

Keywords: form-cue invariance; illusory contours; non-Fourier; optical imaging; second-order.
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