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Orientation integration in detection and discrimination of contrast-modulated patterns

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journal contribution
posted on 2001-01-01, 00:00 authored by Alexander MussapAlexander Mussap
Orientation detection and discrimination thresholds were measured for Gabor ‘envelopes’ formed from contrast-modulation of luminance ‘carriers’. Consistent with previous research differences between carrier and envelope orientation had no effect on sensitivity to envelopes. Using plaid carriers in which the proportion of contrast modulation ‘carried’ by each plaid component was systematically manipulated, it was shown that this tolerance to carrier-envelope orientation difference reflects linear summation across orientation indicative of a single second-stage channel coding for contrast-defined structure. That contrast envelopes did not exhibit linear summation across spatial-frequency, nor across combinations of orientation and spatial-frequency differences, suggests that these second-order channels operate only within certain spatial scales. Using arrays of Gabor micropatterns as carriers in which the orientation distribution of the carriers was manipulated independently of the difference between envelope orientation and mean carrier orientation, it was further demonstrated that the locus of orientation integration must occur prior to envelope detection. In the context of two-stage models that incorporate a non-linearity between the stages, the pattern of results obtained is consistent with the operation of an orientation pooling process between first-stage and second-stage channels, analogous to having all filters of the first-stage feed into all filters of the second-stage within the same spatial-frequency band.

History

Journal

Vision research

Volume

41

Issue

3

Pagination

295 - 311

Publisher

Pergamon

Location

Oxford, England

ISSN

0042-6989

eISSN

1878-5646

Language

eng

Publication classification

C1 Refereed article in a scholarly journal

Copyright notice

2001, Elsevier Science Ltd.