Cherlyn J Ng^1,2 (), Jeannie Pham², Marvin Le², Andrew Browne², Jan Skerswetat²; ¹School of Social Sciences, University of California, Irvine, ²Center for Translational Vision Research, University of California, Irvine

Background: Perceptual sensitivity is limited by neural fluctuations called internal noise. Even when signals exceed the noise level, sampling efficiency determines whether the brain uses information in the signal. Accurate measurements of both are important for understanding cognitive pathologies. However, uncorrected refractive errors present in every eye are often overlooked. These degrade the signal quality even before neural processing begins. When accounted for, the brain may be less noisy, more efficient and more similar across individuals than previously thought. Methods: Residual lower- and higher-order refractive errors in both eyes of 16 healthy 18-45yo participants were measured using the iTrace aberrometer in an ongoing study. All had normal or corrected-to-normal visual acuity. Internal noise and sampling efficiency were determined using the AIM equivalent noise tasks for color and motion (Skerswetat et al., 2024) representing mechanistically distinct aspects of vision. Participants wore their habitual prescription eyewear to perform the task and assess symptoms of visual discomfort (Vinkers et al., 2024). Linear regression was used to correlate optical, perceptual, and discomfort measures. Results: Uncorrected refractive errors increased internal noise for both color and motion perceptions. However, different types of refractive errors distinctly affected each domain. Lower-order aberrations (sphere and astigmatism) impaired color vision. Being large and noticeable, they also prompted complaints about clarity (r=0.66). In contrast, higher-order aberrations that are present in minute amounts affected motion perception without reducing clarity (r=0.80). This finding was paralleled by sampling efficiency, which was also associated only with color but not motion perception (r=0.72). Conclusions: Internal noise and sampling efficiency are often attributed to neural processing. Our findings suggest that focusing errors in the eye are also significant bottlenecks. Effects from disparate types of refractive errors on clarity may reveal neural pathways that use different sources of information for color and motion perceptions.

Acknowledgements: JS was supported by the Alcon Research Foundation Award awarded to AB. JP and ML were supported by the Undergraduate Research Opportunities Program (UROP), University of California, Irvine. AB was supported by NIH/NEI 1K08EY034912 - 01.