Distinct eccentricity-driven dynamics in foveal and extrafoveal visual crowding

Visual crowding-impaired object recognition caused by nearby stimuli-is well documented in peripheral vision and linked to grouping and segmentation. Its spatial extent increases linearly with eccentricity (Bouma's law), consistent with retinal convergence and cortical magnification. Although Bouma's law predicts negligible crowding at the point of fixation, crowding is observed foveally. In the foveola (central 1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>°</mml:mo></mml:math> ), where acuity peaks and photoreceptor-ganglion connectivity is one-to-one, Bouma's law is expected to break, and crowding remain constant. Whether crowding varies across this scale remains unknown. We combined high-resolution eye tracking with gaze-contingent display control to localize gaze and measure crowding thresholds at foveolar eccentricities. Crowding increased linearly within the foveola but with a slope <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>≈</mml:mo></mml:math> 3.5× shallower than in the extrafovea. This effect was robust across observers and conservative fixation criteria. Thus, even in the highest-acuity region, integration zones change with eccentricity, arguing against a uniform central fovea and indicating a distinct crowding regime.