Boundary cue invariance in cortical orientation maps.
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 A 18, 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.
Zhan
Chang'an A
CA
McGill Vision Research Unit, Department of Ophthalmology, McGill University, Montreal, QC, Canada H3A 1A1. changan.zhan@mcgill.ca
Baker
Curtis L
CL
D000818:Animals; D001931:Brain Mapping; D002415:Cats; D015350:Contrast Sensitivity / Q000502:physiology*; D003463:Cues; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005556:Form Perception / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*