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S Sabina Wolfson, Norma V Graham; Exploring the opponent structure of complex (second-order) channels. Journal of Vision 2003;3(9):615. doi: 10.1167/3.9.615.
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To investigate the opponent structure of complex (second-order) channels we ran texture segregation experiments. A complex channel is assumed to have a linear-nonlinear-linear form: linear first-stage receptive fields followed by a pointwise nonlinearity followed by linear second-stage receptive fields.
We consider three structures:
(i) SIGN-but-not-orientation-opponent, (ii) ORIENTATION-but-not-sign-opponent, and (iii) BOTH-orientation-and-sign-opponent.
“Orientation-opponent” means that the small first-stage receptive fields of the complex channel are orthogonal to the large second-stage receptive fields. (“Not-orientation-opponent” means that the receptive fields are of the same orientation.) “Sign-opponent” means that the centers of the second-stage receptive fields are of the opposite sign from the surrounds. (“Not-sign-opponent” means that the sign is the same.)
Our experiments used a forced-choice region-segregation task with element-arrangement patterns composed of vertical and horizontal Gabor patches arranged in checkered or striped patterns.
The results are best fit by the SIGN-but-not-orientation-opponent structure.
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