A common basis for developing visual crowding, collinear facilitation, and contour detection in young children.

Background: Visual crowding, lateral interactions, and contour detection are critical functions for visual perception, context effect, and recognition, but their underlying neural basis is still unclear. The existing models include low-level processing such as receptive field size and the masking effect, but top-down processing such as attention is also considered. It was shown that contour detection developed after six years of age, but the developmental states of crowding and lateral interactions are not known yet. We consider a model in which we assumed that the development of lateral interactions (collinear facilitation), crowding and contour integration in children are correlated. The aim of this study was to explore the development of these visual functions during the early age of 3-6 years in order to better understand the developmental process of these functions and to enable us to probe the critical age when maturation is reached. Results: We found a high degree of crowding, a higher threshold for contour detection, and no collinear facilitation at the age of 3. The thresholds improve with age and approach the adult level by the age of 8 years. The rate of development is correlated among the three phenomena: crowding, collinear facilitation, and contour detection all gradually improve with age. Conclusions: Contrary to visual acuity, which mostly improved within the first year, reaching the adult level at 3 years, crowding is very significant: lateral interaction is suppressive and contour detection is poor. According to our hypothesis, the development of collinear facilitation enables the development of contour detection and the reduction of the crowding effect. These results may support the idea that in young children with a normal visual system there is a common developmental neuronal basis for the mechanisms underlying context processing.