CHAPTER 5

LECTURE EXTENSION

Genetic and Environmental Contributions to High Cognitive Ability among Infants and Preschoolers

Most theories and research on high cognitive ability focus on the mean difference between school-age children with high IQ and the rest of the population and whether this difference is due to genetic or environmental factors. A study by Petrill and his colleagues (Petrill, Saudino, Cherny, emde, Fulker, Hewitt, & Plomin, 1998) extends this work by examining genetic and environmental influences underlying high cognitive ability (g) in infancy and childhood. In this investigation, monozygotic and same-sex dizygotic twin pairs were administered the mental development component of the Bayley Scales of Infant Development at 14, 20, and 24 month, and the Stanford-Binet Intelligence scale at 36 months.

Within each age group, heritability estimates between twins increased from 0.00 at 14 months to 0.64 at 36 months, becoming statistically significant at 24 and 36 months. These results indicate no genetic influence between 14 and 24 months and that in early childhood (24 and 36 months), genetic factors become significant. The authors suggest that this may be due to the fact that language skills become more complex and more extensively measured on tests of cognitive ability during early childhood compared to during infancy. Other analyses indicated significant and substantial heritability estimates among these high g twins averaged across 14, 20, 24, and 36 months, suggesting that genetic influences are largely responsible for the stability of high g across infancy and early childhood.

Petrill, S. A., Saudino, K., Cherny, S. S., Emde, R. N., Fulker, D. W., Hewitt, J. K., & Plomin, R. (1998). Exploring the genetic and environmental etiology of high general cognitive ability in fourteen- to thirty-six-month-old twins. Child Development, 69, 68-74.

LEARNING ACTIVITY

Testing Infants and Toddlers for Object Permanence

The gradual acquisition of object permanence over the sensorimotor stage can be shown by administering the following tasks to infants between 6 and 24 months of age.

SIMPLE OBJECT-HIDING TASK
After attracting the baby's attention, hide a rattle or other attractive toy beneath a cup or under a cloth cover. See if the baby will set aside the obstacle and retrieve the object. Infants between 8 and 12 months generally succeed at this task; younger ones have difficulty.

SUCCESSIVE OBJECT-HIDING TASK
This time, set two cups on the table. Place the toy under one cup (A) and then move it beneath the other (B). Infants between 12 and 18 months of age easily find the object in the second location; younger ones frequently make the well-known AB search error by looking in the first hiding place.

INVISIBLE OBJECT-HIDING TASK
Hide the toy in a small box, place the box under a cover, and, while out of the baby's sight, dump the toy out of the box. Then show the baby the empty box. With the capacity to represent sensorimotor actions internally, infants between 18 months and 2 years of age can usually solve this problem and find the toy.