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Chromatic contrast detection in spatial chromatic noise

Published online by Cambridge University Press:  05 April 2005

GIANLUCA MONACI ,
GLORIA MENEGAZ ,
SABINE SÜSSTRUNK  and
KENNETH KNOBLAUCH
GIANLUCA MONACI
Affiliation:
Signal Processing Laboratory, Swiss Federal Institute of Technology, Lausanne, Switzerland
GLORIA MENEGAZ
Affiliation:
Department of Information Engineering, School of Engineering, University of Siena, Italy
SABINE SÜSSTRUNK
Affiliation:
Audiovisual Communications Laboratory, Swiss Federal Institute of Technology, Lausanne, Switzerland
KENNETH KNOBLAUCH
Affiliation:
INSERM U371, Cerveau et Vision, IFR 19, Institut Fédératif des Neurosciences, Université Claude Bernard Lyon I, Bron cedex, France
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Abstract

The spectral properties of chromatic-detection mechanisms were investigated using a noise-masking paradigm. Contrast-detection thresholds were measured for a signal with a Gaussian spatial profile, modulated in the equiluminant plane in the presence of spatial chromatic noise. The noise was distributed within a sector in the equiluminant plane, centered on the signal direction. Each stimulus consisted of two adjacent fields, one of which contained the signal, separated horizontally by a gap with the same average chromaticity as the uniform background. Observers were asked to judge on which side of the central fixation point the signal was displayed via a two-alternative, forced-choice (2AFC) paradigm. Contrast thresholds were measured for four color directions and three sector widths at increasing levels of the average energy of the axial component of the noise. Results show that contrast thresholds are unaffected by the width of the noise sector, as previously found for temporally modulated stimuli (D'Zmura & Knoblauch, 1998). The results are consistent with the existence of spectrally broadband linear-detection mechanisms tuned to the signal color direction and support the hypothesis of the existence of higher-order color mechanisms with sensitivities tuned to intermediate directions in color space.

Keywords

Chromatic discriminationNoiseSpectral bandwidthMasking
Type
Research Article
Information
Visual Neuroscience , Volume 21 , Issue 3 , May 2004 , pp. 291 - 294
Copyright
© 2004 Cambridge University Press

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