Critical spatial frequencies for illusory contour processing in early visual cortex.

Full Abstract

Single neurons in primate V2 and cat A18 exhibit identical orientation tuning for sinewave grating and illusory contour stimuli. This cue invariance is also manifested in similar orientation maps to these stimuli, but in V1/A17 the illusory contour maps appear reversed. We hypothesized that this map reversal depends upon the spatial frequencies of the inducers in the illusory contours, relative to the spatial selectivities of these brain areas. We employed intrinsic signal optical imaging to measure orientation maps in cat A17/18 to illusory contours with inducers at spatial frequencies from 0.15 to 1.6 cpd. A17 illusory contour maps were indeed reversed compared with grating-driven maps for inducer spatial frequencies <1.3 cpd, whereas A18 maps were invariant. Simulations based on known neurophysiology demonstrated that map reversal can arise from linear filtering, and map invariance can be explained by a nonlinear (filter-rectify-filter) mechanism. The simulation also correctly predicted that A17 could show invariant maps when the inducer spatial frequency is sufficiently high (1.6 cpd), and that A18 maps could reverse at lower inducer frequencies (0.18 cpd). Thus, the map reversal or invariance to illusory contours depends critically on the relationship of the inducer spatial frequencies to the spatial filtering properties of neurons in each brain area.

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Author information

Author/s: Zhan, Chang'an A (CA); Baker, Curtis L (CL);

Affiliation: Department of Physiology, McGill University, Montreal, QC, Canada.

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't

Journal: Cerebral cortex (New York, N.Y. : 1991) (Cereb Cortex), published in United States. (Language: eng)

Reference: 2008-May; vol 18 (issue 5) : pp 1029-41

Dates: Created 2008/04/11; Completed 2008/06/11;

PMID: 17693395, status: MEDLINE (last retrieval date: 11/6/2008)

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Animals
Brain Mapping
Cats
Computer Simulation
Contrast Sensitivity - physiology
Form Perception - physiology

Illusions - physiology
Models, Neurological
Neurons - physiology
Orientation - physiology
Photic Stimulation
Visual Cortex - cytology; physiology

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