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Modeling visual performance differences 'around' the visual field: A computational observer approach
Eline R Kupers1, Marisa Carrasco1,2, Jonathan Winawer1,2
1Department of Psychology, New York University, New York, New York, United States of America.
Plos Computational Biology
|May 25, 2019
Summary
Visual performance varies across the visual field, with early visual factors like optics and cone density explaining only a small portion of these differences. Later visual processing stages likely account for significant performance asymmetries.
Area of Science:
- Vision science
- Computational neuroscience
- Psychophysics
Background:
- Visual performance varies significantly with polar angle, independent of eccentricity.
- These performance differences around the visual field can be substantial, comparable to changes in eccentricity.
- The underlying causes for these visual performance asymmetries are not fully understood.
Purpose of the Study:
- To investigate the contribution of early visual factors, specifically optical quality and cone density, to polar angle-dependent performance differences.
- To quantify how much optical quality and cone density can explain observed psychophysical variations in visual tasks.
- To determine if known variations in eye optics and photoreceptor density account for performance asymmetries.
Main Methods:
- Developed a computational observer model using ISETBIO software.
- Simulated an orientation discrimination task, modeling photon emission, human optics with eye movements, and retinal cone isomerizations.
- Employed a support vector machine to classify stimulus orientation based on photon absorptions.
Main Results:
- The computational model, simulating early visual processing, required extreme changes in optical defocus or cone density to match observed psychophysical contrast thresholds.
- Simulated optical quality changes of ~7 diopters or cone density changes of 500% were needed to replicate a 30% increase in contrast thresholds.
- These required parameter changes far exceed the actual variations observed in human eyes as a function of polar angle.
Conclusions:
- Early visual factors, including optical quality and cone density, account for only a minor fraction of the observed polar angle asymmetries in visual performance.
- Significant asymmetries in visual performance must originate from later stages of visual processing, such as retinal or cortical pathways.
- The study highlights the need to investigate neural processing beyond the earliest visual stages to understand visual field variations.
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