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Karin Stromswold, Michelle Rosenthal, Kruti Patel, Diane Molnar; Development of Visual-Motor Integration: The Role of Genetic & Environmental Factors. Journal of Vision 2011;11(11):462. doi: https://doi.org/10.1167/11.11.462.
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© ARVO (1962-2015); The Authors (2016-present)
BACKGROUND. Integrating visual information and motor actions, Visual Motor Integration (VMI), is necessary to perform tasks as simple as picking up a spoon and as complex as writing. Despite VMI's importance and the fact that VMI is impaired in genetic disorders such as Williams Syndrome (see Georgopolous et al., 2004) and Shwachman-Diamond Syndrome (see Kerr et al., 2010), little is known about the role of heritable and environmental factors in typically-developing children's VMI.
METHODS. We tested 125 pairs of typically-developing twins who were between 3 and 12 years old. As is typically done, VMI was assessed via a figure-copying task. Our test was modeled after the Beery-Buktenica Test (2004) and had 6 figures (see Figure 1). Each figure was assessed along 4 dimensions, with each dimension scored on a 1 to 5 scale.
RESULTS. Age was highly correlated with total copying score (r = .83, p < .00001, see Figure 2). Heritable factors accounted for 78% of the variance in 3- and 4-year olds' copying scores and 98% of the variance in 5- and 6-year olds' copying scores. In striking contrast, heritable factors explained little or none of the variance in older children's copying scores.
DISCUSSION. One possible explanation is that VMI does have a strong genetic component for typically-developing children's VMI skills. However, because schools explicitly teach children how to copy letters, numbers and shapes, as children get older, the impact of environmental factors such as quality of instruction swamps the impact of heritable factors on copying. If this account is correct, other non-copying measures of VMI could yield substantial heritabilities for both younger and older children. A second possible explanation is that genetic factors influence the rate of development of VMI abilities, but not the level of VMI ability eventually obtained.
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