Purchase this article with an account.
Gayathri Srinivasan, Erwin Wong; Reduced second-order contrast discrimination under dichoptic viewing. Journal of Vision 2009;9(8):1015. doi: 10.1167/9.8.1015.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose. Past studies have shown that second-order contrast discrimination under monocular and binocular viewing produces a ‘dipper function’ similar to that seen for first-order contrast. Here we investigate second-order contrast discrimination under dichoptic viewing. We expected a reduced dipper function, likely attributable to interocular gain mechanisms acting on the first-order carrier.
Methods. Four observers (two naäve and the two authors) participated. Stimuli were presented via computer and the CRT was viewed through a mirror haploscope with septum. Second-order stimuli were amplitude-modulated sinusoids (carrier 8 c/deg, envelope 1 c/deg, σ = λ, 4° diameter patch, sinusoids horizontal). We used a temporal 2-AFC (500 msec intervals) with the MOCS. We measured increment thresholds for a range of pedestal contrasts (0.1–4.0) for three normalized carrier contrasts (2.5×, 5× and 10× contrast detection threshold (CDT)) under monoptic (control) and dichoptic viewing.
Results. Observers on average showed facilitation of target detection at subthreshold and near threshold pedestal contrasts, with monoptic viewing producing more facilitation than dichoptic viewing. The dichoptic effect was dependent on carrier contrast: on average, the maximum facilitation produced by the 2.5×, 5×, and 10× CDT was 5–25%, 0–22%, and 0–10%, respectively. That is, lower carrier contrast produced greater facilitation of second-order contrast detection. In contrast, the monoptic effect was independent of carrier contrast: maximum facilitation 0–17% for all CDT. Furthermore, suprathreshold pedestal contrasts produced similar trends: monoptic viewing produced marked suppression (maximum 150–330%), dichoptic viewing produced less suppression (maximum 0–110%), and only dichoptic showed dependence on carrier contrast.
Conclusions. The results suggest that discrimination of second-order contrast is dependent on the carrier (first-order) contrast for dichoptic viewing but much less for monoptic viewing. This likely reflects an increase in contrast gain for interocular combination of first-order contrast that limits the input to the second-order stage.
This PDF is available to Subscribers Only