Visual development and plasticity in children

Abstract

The effects of visual experience on perception were examined using two classic research paradigms: visual deprivation and perceptual adaptation. The present study evaluates the extent to which children in the 5- to 14-year-old age range have the capacity for visual plasticity with respect to recovery from the effects of astigmatism-related visual deprivation and adaptation to spatially distorted visual input. Visual experience was altered through eyeglass correction of astigmatism, a condition of the eye that induces degraded (blurred) visual input and causes a form of visual deprivation. Lenses that correct astigmatism cause two changes in sensory input: they alleviate the deprivation effects of astigmatism, and cause spatial distortion. Perception was initially measured when the children first received eyeglass correction, and change in perception was measured after 1 month of wear, and after 1 year of wear. Measures included recognition acuity, resolution acuity, vernier acuity, contrast sensitivity, stereoacuity, and form perception. Baseline analyses of normal (non-astigmatic) subject data indicated that recognition acuity, resolution acuity, vernier acuity, and contrast sensitivity continue to develop within the 5- to 14-year-old age range. Baseline analyses also revealed that children who experienced astigmatism-related deprivation demonstrated perceptual deficits, in comparison to non-astigmatic children, on all measures of perception (although deficits within some measures depended on stimulus orientation (grating acuity and contrast sensitivity) and spatial frequency of the stimulus (for contrast sensitivity)), and demonstrated measurable distortions in form perception. However, primary outcome analyses revealed little evidence of plasticity with regard to recovery from the effects of deprivation and no evidence of plasticity with regard to perceptual adaptation to distortion. The results suggest that children in the 5- to 14-year-old age range may be beyond the sensitive period for recovery from astigmatism-related deprivation through simple restoration of clear visual input. Discussion focuses on theoretical views on conditions necessary for plasticity (Bedford, 1993a, 1993b, 1995, Banks, 1988), and their implications regarding another intervention, discrimination learning, that might be more effective at inducing plasticity in children and adults who are beyond the sensitive period for plasticity, and their implications for interpretation of data on adaptation to spatial distortion observed in the present study.