The development of visual acuity and crowding reveals the slow fine-tuning of foveal vision

Abstract

Abstract The adult visual system is characterised by high-resolution foveal vision and a peripheral field limited by crowding, the disruption to object recognition in clutter that gives a summary ‘gist’ over fine detail. In children, crowding is elevated foveally, with the estimated age where foveal crowding drops to adult-like levels varying widely from 5 to 12+ years. As crowding restricts key processes like reading, characterisation of this developmental trajectory is critical. Using methods optimised to measure crowding in children, adults and typically-developing children ( n  = 119; 3–13 years) judged the orientation of a foveal ‘VacMan’ target either in isolation or surrounded by ‘ghost’ flankers. For isolated elements, acuity (measured as gap-size thresholds) dropped rapidly to adult-like levels at 5–6 years. Thresholds rose when flanked/crowded, with elevations highest at 3–4 years, persisting at 5–6 years, and dropping to adult-like levels at 7–8 years. A meta-analysis of our results and 13 prior studies reveals a consistent developmental trajectory, despite wide methodological variations. We further demonstrate that developmental crowding shows the same selectivity for target-flanker similarity as peripheral crowding, consistent with common mechanisms. This prolonged development reveals a shifting balance in the visual system between the processing of fine detail vs. the ‘gist’ of the scene.