The development of visual acuity and crowding: Finding the balance between fine detail and 'gist' processing

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' in place of fine detail. In children, crowding is elevated in the fovea, with estimates of the age where foveal crowding drops to adult-like levels varying widely from 5 to 12+ years. As crowding restricts key processes like reading, better characterisation of this developmental trajectory is critical. We developed methods optimised to measure crowding in children, whereby adults and typically developing children aged 3-13 years (n=119) judged the orientation of a foveal 'VacMan' target either in isolation or surrounded by 'ghost' flankers. Stimulus sizes and separation were scaled adaptively. In the isolated condition, acuity (measured as gap-size thresholds) dropped rapidly to adult-like levels at 5-6 years. Thresholds rose when flankers were added, demonstrating foveal crowding at all ages. These elevations were highest at 3-4 years and persisted at 5-6 years, dropping to adult-like levels at 7-8 years. A meta-analysis of our thresholds and those from 11 prior studies reveals the same overall developmental trajectory, despite widely varying stimuli and procedures, with some divergent estimates likely driven by measurement confounds such as underestimated adult crowding levels. We further demonstrate that developmental foveal crowding shows the same selectivity for target-flanker similarity as peripheral crowding, consistent with common mechanisms. This prolonged development of crowding reveals a shifting balance in the visual system between the processing of fine detail vs. the 'gist' of the scene.