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BrainTrace: cortical encoding of visual acuity under myopic blur

Poster Session D - Monday, March 9, 2026, 8:00 – 10:00 am PDT, Fairview/Kitsilano Ballrooms

Katia steinfeld¹ (katia.steinfeld@unil.ch), Olivier Collignon^2,3, Micah Murray^1,3; ¹Lausanne University and University Hospital, Switzerland, ²University of Louvain, Belgium, ³The Sense Institute, Switzerland

Myopic defocus degrades visual acuity and is thought to play a causal role in axial eye growth, yet its cortical consequences remain incompletely characterized. Electrophysiological studies of blur have largely relied on visual evoked potential amplitude changes, providing limited insight into how optical noise alters neural encoding. Here, we introduce a fast periodic visual stimulation (FPVS) protocol combined with EEG to objectively track how myopic blur alters the cortical encoding of angular visual acuity. Adults (n = 10) with corrected-to-normal vision viewed rapid sequences of size-matched Landolt C optotypes and annuli presented in a 2:1 base:oddball ratio, such that discrimination of the Landolt C gap selectively elicited neural responses at the oddball frequency and its harmonics. Optical blur was simulated by convolving stimuli with point-spread functions derived from Zernike polynomials corresponding to myopic defocus levels of 0 diopters (D), −1 D, and −3 D (negative control). Neural entrainment was quantified over occipital channels using signal-to-noise ratio and Z-score analyses at the group level. Entrainment at the base frequency remained robust across all blur levels, confirming reliable visual stimulation, while Z-scores decreased with increasing blur. In contrast, oddball-frequency entrainment were significant for 0 D and −1 D blur, indicating successful neural discrimination of the Landolt C gap, but were absent in the −3 D condition, when the Landolt C and annulus were perceptually indistinguishable. Critically, Z-scores at the oddball frequency decreased with increasing blur over occipital cortex.This protocol provides separable neural indices of stimulus visibility and feature discriminability, allowing to parse how optical blur and other forms of external sensory noise limit visual encoding. Overall, it offers a rapid, objective neural marker of angular visual acuity under sensory degradation.

Topic Area: PERCEPTION & ACTION: Vision