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Proceedings Paper

Perceived structure of plaids implies variable combination of oriented filters in edge finding
Author(s): Mark A. Georgeson; Tim S. Meese
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Paper Abstract

Orientation-tuned spatial filters in visual cortex are widely held to act as 'orientation detectors,' but our experiments on the perception of stationary 2-D plaids require a new view. When two sinusoidal gratings at different orientations (say 1 c/deg, plus or minus 45 deg from vertical) are superimposed to form a standard plaid they do not in general look like two sets of oblique contours (diamonds) but more like a blurred checkerboard (squares) with vertical and horizontal edges, although the Fourier components are oblique. The pattern of edges seen in this plaid and others corresponds to the zero-crossings (ZCs) in the output of a circular filter, but adaptation and masking experiments suggest that oriented filters are being summed to emulate circular filtering, before ZC analysis. At low contrasts or after adaptation to an intermediate orientation, the combination can fail or be 'broken,' and the diamond structure of the components is seen instead. Adding a low contrast 3rd harmonic to one or both components in square-wave phase also changed the plaid's appearance from squares to diamonds, but adapting to the 3rd harmonic enhanced the square appearance. Filters can evidently switch from combining across orientation to combining across spatial frequency, perhaps reflecting a preference for sharp edges. The combination stage of edge detection may involve variably weighted summing of oriented filters in monocular pathways, and the idea of 'orientation detectors' is no longer useful for understanding the perceived spatial structure of these 2-D plaid images.

Paper Details

Date Published: 22 April 1996
PDF: 15 pages
Proc. SPIE 2657, Human Vision and Electronic Imaging, (22 April 1996); doi: 10.1117/12.238714
Show Author Affiliations
Mark A. Georgeson, Univ. of Birmingham (United Kingdom)
Tim S. Meese, Aston Univ. (United Kingdom)

Published in SPIE Proceedings Vol. 2657:
Human Vision and Electronic Imaging
Bernice E. Rogowitz; Jan P. Allebach, Editor(s)

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