Interocular suppression patterns in binocularly abnormal observers using luminance- and contrast-modulated noise stimuli

Abstract

In binocular viewing, images presented to the amblyopic eye are suppressed in the cortex to prevent confusion or diplopia. The present study measures depth and extent of interocular suppression across the central circular 24° visual field in observers with strabismus and microstrabismus. Visual stimuli were concentric rings of alternating polarity, each divided into sectors. Rings were defined by luminance (L), luminance-modulated noise (LM), or contrast-modulated noise (CM). They were viewed binocularly except for the tested ring, which was viewed dichoptically, so that the modulation of one sector presented to the weaker or amblyopic eye was adjusted to perceptually match the surrounding ring presented to the preferred eye. A two alternative forced-choice paradigm combined with a staircase procedure allowed for measurement of the point of subjective equality, or perceptual match. Depth of suppression was calculated as the difference between physical modulations presented to the two eyes at this point. Strabismic participants showed suppression deeper centrally than peripherally, and in one hemifield of the visual field more than the other. Suppression was deeper for L than LM, and CM than LM stimuli. Microstrabismic suppression was weaker than that of strabismics, central for L and LM stimuli, with suppression of CM stimuli being broader, deeper and more in one hemifield. Suppression depth was positively correlated with interocular visual acuity difference and stereoacuity reduction. Clinically, LM stimuli could be used for assessment of deeper amblyopes to assess suppression patterns, while more sensitive detection of mild suppression would be possible using CM stimuli.

Orientation Tuning and Contrast Dependence of Continuous Flash Suppression in Amblyopia and Normal Vision

“…Patient LW, who had mild amblyopia, showed equal suppression between eyes, which is consistent with previous studies reporting positive correlations between amblyopia severity and suppression strength. [4][5][6][7][8][9] Overall, however, we did not observe significant correlations between suppression of the amblyopic eye and clinical measures of amblyopia severity. The extensive testing time required in this study limited our sample size and CFS noise contrast also varied within the amblyopic group; therefore, the correlation results should be interpreted cautiously (see Supplementary Results for further details).…”

“…Previous studies using dichoptic global motion, 4,44 phase matching, 5,45 and other contrast-or luminance-balancing suppression measures 6,8 report greater average suppression in patients with amblyopia than controls. However, these previously established methods (including the dichoptic global motion test used in this study) measure the interocular balance of suppression and do not account for monocular deficits.…”

“…Greater imbalances in interocular suppression are correlated with greater interocular differences in visual acuity and worse stereoacuity. [4][5][6][7][8][9] Unbalanced interocular suppression in amblyopia has been advocated as a target mechanism for binocular therapy, with the rationale that rebalancing interocular suppression may improve visual functions. [10][11][12] In animals with experimentally induced amblyopia, ocular dominance in the visual cortex favors the fellow eye, 13,14 interocular suppression appears to increase relative to binocular excitation, [15][16][17] and normal orientation matching of inputs from the two eyes are disrupted.…”

Interocular ND filter suppression: Eccentricity and luminance polarity effects

“…Current models of both normal and abnormal binocular vision suggest that binocular performance reflects a balance between suppression and excitation between eyes (Baker, Meese, & Hess, 2008;Ding, Klein, & Levi, 2013a;Ding, Klein, & Levi, 2013b). Previously we found that interocular suppression in amblyopes was luminance-polarity dependent, with luminance increments (or white stimuli) being suppressed more strongly than luminance decrements (or black stimuli) (Chima et al, 2016). A polarity dependence was not noted for interocular suppression generated with unilateral blur, which was broad, extending across the central 24°field (Chima et al, 2015).…”

“…To prevent confusion (where two different objects are perceived at the same location) or diplopia (where one object is perceived at two different locations), one image is cortically suppressed (Sengpiel, Blakemore, Kind, & Harrad, 1994). Interocular suppression is present in amblyopia (e.g., Black, Thompson, Maehara, & Hess, 2011;Chima, Formankiewicz, & Waugh, 2016;Irvine, 1948;Li et al, 2013;Mehdorn, 1989;Travers, 1938). It is also present in observers with normal binocular vision, when binocularly viewing stimuli in the presence of unilateral blur (Chima, Formankiewicz, & Waugh, 2015;Pianta & Kalloniatis, 1998;Simpson, 1991) or when a neutral density (ND) filter is placed before one eye (Baker, Meese, Mansouri, & Hess, 2007;Li et al, 2012;Li et al, 2013;Zhang, Bobier, Thompson, & Hess, 2011;Zhou, Jia, Huang, & Hess, 2013).…”