Interocular Suppression as Revealed by Dichoptic Masking Is Orientation-Dependent and Imbalanced in Amblyopia

Balanced, Orientation-Dependent Dichoptic Masking in Cortex of Visually Normal Humans Measured Using Electroencephalography (EEG)

“…Gong et al [2] recently reported psychophysical findings consistent with our electrophysiological findings. They measured normal observers’ contrast detection thresholds for Gabor targets in one eye and oriented noise masks, or a uniform, mean-luminance field, in the fellow eye.…”

“…This combination provides the basis for single, clear, and comfortable vision. Previous work, including psychophysical studies in humans [2] and intracortical recordings in nonhuman primates [3], has shown that activity in the visual cortex arising from dichoptic presentation (i.e., when each eye views independent stimuli simultaneously) results in a mutually inhibitory effect – i.e., the signals from each eye act to reduce one another. This inhibitory mechanism, known as interocular suppression, is abnormal in individuals who suffer traumatic brain injury or who have experienced abnormal visual stimulation during development (e.g., as is the case in amblyopia) [4], [5], [6].…”

“…EEG is a non-invasive, objective measure of neural activity in visual cortex. Previous psychophysical and electrophysiological studies (see Discussion) have indicated that interocular suppression in the normal visual system is orientation-dependent when invoked using a dichoptic masking paradigm [2], [8], [9], [10], [11]. Here, in a cohort of normal participants, we recorded VEPs in response to vertical and/or horizontal sine-wave gratings presented dichoptically.…”

The Orientation Selectivity of Dichoptic Masking Suppression is Contrast Dependent in Amblyopia

“…The paradigms and spatial frequencies used in these previous studies were different. In our recent study, 30 we used a dichoptic masking paradigm and measured interocular suppressive interaction of both eyes for a range of spatial frequencies in amblyopes and found that such orientationally tuned interocular suppression was observed in low to mid spatial frequency in both eyes, but not at high spatial frequency for the amblyopic eye. These studies suggest that the orientation selectivity of interocular suppression in amblyopia is spatial frequency dependent.…”

A Dichoptic Optokinetic Nystagmus Paradigm for Interocular Suppression Quantification in Intermittent Exotropia

“…Though these tests are easy to operate, they are in fact subjective qualitative assessments to evaluate visual suppression from the foveal region of the fixating eye to the non-foveal region of the deviated eye in IXT patients when they exhibit exodeviation ( Baker et al, 2008 ; Wen et al, 2018 ), thus the foveal-foveal suppression remains unknown. Meanwhile, electrophysiological ( Brown et al, 1999 ; Zheng et al, 2019 ) and neuroimage ( Lygo et al, 2021 ) methods as well as several established psychophysical paradigms, including the global motion coherence threshold, orientation coherence, and interocular phase combination ( Narasimhan et al, 2012 ; Ding et al, 2013 ; Zhou et al, 2013 ; Wang et al, 2019 ; Zheng et al, 2019 ; Gong et al, 2020 ; Lygo et al, 2021 ), have been devised to quantify suppression. These subjective assessments require attention and certain responses from patients during evaluation, making them more difficult for young children.…”