Development of gross and fine visuo-motor ability: Insights from late-sighted children

Grasping an object relies on an integration of gross- and fine-visuo-motor abilities, combining large-scale movements for reaching and hand orienting with precise finger movements ensuring a secure grasp. The acquisition of this intricate ability is influenced by many factors, including sensory processing, motor skill, physiological maturation of neural pathways, and experiential learning. Untangling the individual impact of these factors on visuo-motor development proves challenging given their concurrent progression during typical child development. Here we report an attempt to isolate the impact of visual experience on gross and fine visuo-motor development. We investigated the effects of visual restoration on individuals born with bilateral dense cataracts. These patients had attained neural and motor maturity while remaining visually inexperienced until undergoing cataract-removal surgery in late childhood (as part of Project Prakash). Fourteen patients were tasked with visually guided two-finger pincer grasping of irregularly shaped flat objects (Goodale, 1994). Pre- and repeated post-operative assessments allowed us to track longitudinal changes in visuo-motor measures. Results reveal a developmental progression in gross visuo-motor ability, with all patients demonstrating an increased reach-to-grasp speed, matching the speed of age- and acuity-matched controls within one year after surgery. Most also exhibited enhanced hand orientation variability, indicating adaptation to diverse object orientations. However, challenges persisted in fine visuo-motor ability for most patients, with only three achieving enhanced reliability, and two of these reaching computational optimality in grasping efficiency within a year. Our findings suggest that gross visuo-motor ability can be acquired following late sight restoration, but fine visuo-motor proficiency may suffer permanent compromise, or at least require prolonged experience. Ongoing follow-up beyond one year aims to uncover potential later-stage improvements and explore individual differences in long-term improvement. Our results point to the nuanced interplay between visual experience and visuo-motor development, providing insights for tailored interventions for visuo-motor skill acquisition.