Linear binocular combination of responses to contrast modulation: contrast-weighted summation in first- and second-order vision

Jiawei Zhou, Mark A. Georgeson, Robert F. Hess*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Binocular combination for first-order (luminancedefined) stimuli has been widely studied, but we know rather little about this binocular process for spatial modulations of contrast (second-order stimuli). We used phase-matching and amplitude-matching tasks to assess binocular combination of second-order phase and modulation depth simultaneously. With fixed modulation in one eye, we found that binocularly perceived phase was shifted, and perceived amplitude increased almost linearly as modulation depth in the other eye increased. At larger disparities, the phase shift was larger and the amplitude change was smaller. The degree of interocular correlation of the carriers had no influence. These results can be explained by an initial extraction of the contrast envelopes before binocular combination (consistent with the lack of dependence on carrier correlation) followed by a weighted linear summation of second-order modulations in which the weights (gains) for each eye are driven by the first-order carrier contrasts as previously found for first-order binocular combination. Perceived modulation depth fell markedly with increasing phase disparity unlike previous findings that perceived first-order contrast was almost independent of phase disparity. We present a simple revision to a widely used interocular gain-control theory that unifies first- and second-order binocular summation with a single principle-contrast-weighted summation-and we further elaborate the model for first-order combination. Conclusion: Second-order combination is controlled by first-order contrast.

Original languageEnglish
Article number24
Number of pages19
JournalJournal of Vision
Issue number13
Publication statusPublished - 30 Nov 2014

Bibliographical note

© 2014 ARVO

Funding: CIHR grant (#53346); NSERC grant (#46528-11); and BBSRC grant (BB/


  • binocular combination
  • binocular disparity
  • contrast modulation
  • contrastgain control
  • first-order
  • interocular suppression
  • rivalry suppression
  • second-order


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