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Erwin Wong; Characteristics of dichoptic lateral masking of contrast detection. Journal of Vision 2010;10(7):1368. doi: 10.1167/10.7.1368.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. Past studies show strong effects by flanks on contrast detection. A limited dichoptic study showed no net flank effect (Huang et al., 2006). Here we more extensively investigate dichoptic lateral masking. Methods. Observers: 5 adults with normal vision and 2 non-binocular, non-amblyopic (NBNA) adults. Measure: contrast detection threshold (CDT) for a sinusoid (3 c/deg, 2° diameter, vertical) in isolation and with two flanking sinusoids at 3 separations (edge to edge 0.5° overlap, abutting, 0.5° separation). Flanks: target sinusoid (normalized 1.5x and 3x flank CDT) oriented vertical or horizontal, or Gaussian blobs (2° diameter) normalized by the flank CDT. Presentations: target to dominant eye, flanks monoptic (abutting only) or dichoptic (3 separations), 2-AFC with the MOCS, and mirror haploscope with septum. Results. For the normal observers, monoptic viewing produced facilitation by collinear flanks (mean 10%±4% (95% CI)), no effect from orthogonal, and suppression by blobs (8%±6%). These effects were greater for 3x CDT flanks and this difference was not shown under dichoptic viewing. For dichoptic viewing, the overlap condition produced facilitation by collinear flanks (7%±4%), suppression by orthogonal (4%±4%), and no effect by blobs. The abutting condition produced facilitation by collinear flanks (8%±4%) and orthogonal (7%±5%), and no effect by blobs. The separation condition produced suppression by collinear flanks (9%±5%), orthogonal (6%±3%), and blobs (8%±4%). For the NBNA observers, under monoptic and dichoptic viewing all separations showed suppression by collinear flanks (14%±7%), orthogonal (10%±8%) and blobs (8±4%). Conclusions. Dichoptic integration of contrast across space is similar to the known monocular mechanism: facilitation by flanks slightly overlapping or abutting the target, and masking only via spatial channels (blobs had little effect). However, an exclusive dichoptic mechanism is suggested: flanks suppress rather than have no effect when separated from the target. Dichoptic integration is further supported by the suppression shown by the NBNA observers.
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