Contour interaction function in the preschool child.

Contour interaction was investigated in 12 preschool children 3 to 4 years of age, and compared to the results obtained from 5 normal adults tested under an identical paradigm. Observers viewed the display from a distance at which they could identify the location of a gap (up or down) in an isolated C correctly on 90 to 95% of the trials. The isolated C and C's with bars tangentially located at various positions above and below the test optotype were intermixed randomly. Percent correct was plotted as a function of the angular subtense of the gap width of the test optotype. A significant decrease in performance was found when the bars were positioned at 0.71 to 1.42 times the angular subtense of the gap for both the preschool children and the adults. The results suggest that preschool children demonstrate contour interaction that is quantitatively similar to adults. Because the spacing of letters on standard acuity charts is typically larger than the range over which contour interaction occurs, the poorer acuity often measured with charts compared to isolated letter presentation in preschool children suggests that factors other than contour interaction (perhaps attentional factors) are involved.