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. 2018 Sep;38(5):525-537.
doi: 10.1111/opo.12581. Epub 2018 Sep 16.

Binocular contrast summation and inhibition depends on spatial frequency, eccentricity and binocular disparity

Concetta F Alberti  1 , Peter J Bex  1
Affiliations

Binocular contrast summation and inhibition depends on spatial frequency, eccentricity and binocular disparity

Concetta F Alberti et al. Ophthalmic Physiol Opt. 2018 Sep.

Abstract

Purpose: When central vision is compromised, visually-guided behaviour becomes dependent on peripheral retina, often at a preferred retinal locus (PRL). Previous studies have examined adaptation to central vision loss with monocular 2D paradigms, whereas in real tasks, patients make binocular eye movements to targets of various sizes and depth in 3D environments.

Methods: We therefore examined monocular and binocular contrast sensitivity functions with a 26-AFC (alternate forced choice) band-pass filtered letter identification task at 2° or 6° eccentricity in observers with simulated central vision loss. Binocular stimuli were presented in corresponding or non-corresponding stereoscopic retinal locations. Gaze-contingent scotomas (0.5° radius disks of pink noise) were simulated independently in each eye with a 1000 Hz eye tracker and 120 Hz dichoptic shutter glasses.

Results: Contrast sensitivity was higher for binocular than monocular conditions, but only exceeded probability summation at low-mid spatial frequencies in corresponding retinal locations. At high spatial frequencies or non-corresponding retinal locations, binocular contrast sensitivity showed evidence of interocular suppression.

Conclusions: These results suggest that binocular vision deficits may be underestimated by monocular vision tests and identify a method that can be used to select a PRL based on binocular contrast summation.

Keywords: binocular inhibition; binocular summation; contrast sensitivity; disparity; peripheral vision.

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Conflict of interest statement

Disclosures: The author CFA reports no conflicts of interest and has no proprietary interest in any of the materials mentioned in this article. The author PJB reports: Adaptive Sensory Technology, Personal Financial Interest; Adaptive Sensory Technology, Patent.

Figures

Figure 1.
Figure 1.
Monocular and Binocular Contrast Sensitivity Functions. Data show contrast sensitivity from the quickCSF algorithm at 16 spatial frequencies for corresponding (left column) and non-corresponding (right column) conditions at 2° (top row) and 6° (bottom row) eccentricities. Boxplots show medians and interquartile range (error bars) of ten observers (2° eccentricity) or 5 observers (6° eccentricity), with left eye and right eye data combined in the monocular data, dots show outliers. Monocular acuities are replotted for comparison in both columns. Significant binocular-monocular contrast sensitivity differences for each spatial Frequency are marked as asterisks, where *=p<0.05; **=p<0.01 and ***=p<0.001.
Figure 2.
Figure 2.
Monocular and Binocular Acuity. Data show CSF Acuity (c/deg) for corresponding (left column) and non-corresponding (right column) Conditions at 2° (top row) and 6° (bottom row) eccentricities. Boxplots show medians and interquartile range (error bars) of ten observers (2°) or five observers (6°), with left eye and right eye data combined in the monocular data, dots show outliers. Monocular acuities are replotted for comparison in both columns.
Figure 3.
Figure 3.
Monocular and Binocular AULCSF. Data show AULCSF for corresponding (left column) and non-corresponding (right column) conditions at 2° (top row) and 6° (bottom row) eccentricities. Boxplots show medians and interquartile range (error bars) of ten observers (2°) or five observers (6°), with left eye and right eye data in the monocular data, dots show outliers. Monocular AULCSF is replotted for comparison in both columns.
Figure 4.
Figure 4.
Binocular Contrast Summation as a function of Spatial Frequency. Data show the ratio of observed binocular probability summation over expected binocular probability summation (P Observed Binocular /P Expected binocular) at 16 spatial frequencies for corresponding (left column) and non-corresponding (right column) conditions at 2° (top row) and 6° (bottom row) eccentricities. A value of 1 indicates simple probability summation between independent monocular sensors while a value greater than 1 or lower than 1 indicates a binocular integration mechanism or a binocular inhibition mechanism respectively. Boxplots show medians and interquartile range (error bars) of ten observers (2° eccentricity) or 5 observers (6° eccentricity). The dots are outlier points. Significant binocular contrast summation/inhibition vs probability summation t-tests for each spatial frequency are marked as asterisks.
Figure 5.
Figure 5.
Contrast sensitivity functions for stimuli presented monocularly in binocular corresponding and non-corresponding conditions. Boxplots show medians and quartiles (error bars) of 10 observers. The dots are outlier points.
Figure A1.
Figure A1.
Contrast Summation Ratio as a function of Spatial Frequency. Data show the summation ratio (in dB) between the monocular and the binocular thresholds at 16 spatial frequencies for corresponding (left column) and non-corresponding (right column) conditions at 2° (top row) and 6° (bottom row) eccentricities. Boxplots show medians and interquartile range (error bars) of ten observers (2° eccentricity) or 5 observers (6° eccentricity). The dots are outlier points.
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