Rice study links male birth weight to cognitive development

Rice study links male birth weight to cognitive development

BY PAM SHERIDAN
Special to the Rice News

A Rice University study has found that normal birth weight — at least, among male infants — is related to how readily they focus on a visual stimulus, an ability that later may play a role in some attention deficit hyperactivity disorders.

Rice psychologist James Dannemiller’s research suggests that even small variations among infants born within a normal weight range are related to their early cognitive development, which further emphasizes the importance of prenatal care.

“Infant boys who are heavier at birth, but within the normal weight range, are more likely to focus toward a visual stimulus,” said Dannemiller, the Lynette S. Autrey Professor in Psychology.

Dannemiller’s study is one of the first to show how birth weight in the normal range can have a measurable effect on this aspect of infant development.

“On the other hand, while girls visually orient on average as well as boys, their birth weights appear to have no connection to this type of attention,” he said.

Visual orienting may be involved in some types of attention deficit hyperactivity disorder (ADHD). “While ADHD is often thought of as an inability to sustain attention, it also may be the result of overactive orienting, with anything in the environment grabbing the person’s attention,” Dannemiller said.

In his study published in the journal Infant Behavior and Development, Dannemiller focused on visual orienting as one of the earliest dimensions of infants’ typical development.

“Visual orienting is the earliest and most-developed of our abilities to focus and plays a role in our cognitive development,” he said. “The fact that it is associated with something physiological, namely birth weight, suggests the further importance of prenatal development.”

Dannemiller also discovered that babies with birth weights of more than 10 pounds showed less inclination to orient their eyes toward a visual stimulus. One of the causes of this condition, called “macrosomia,” is uncontrolled diabetes in mothers during pregnancy. However, none of the mothers of the 30 macrosomic infants in Dannemiller’s sample had this disorder.

“Currently, I am gathering more details on the pregnancies of these mothers to determine the reasons behind their babies’ high weights and why, in their cases, the ability to orient decreased for both male and female infants,” he said.

To examine the relation between birth weight and visual orienting, Dannemiller studied a sample of 944 infants between 2 and 5 months old. Information about the babies’ birth weight and gestational age was collected from the parents.

The babies were repeatedly shown a display with small, vertical bars randomly distributed across a monitor. One of these bars either on the right or the left of the screen oscillated horizontally. In half of the trials the movement was located on the left side of the screen, and in the other half on the right. To gauge where the babies’ eyes focused, Danemiller positioned observers so they were able to see if infants’ eyes moved to the left or right, but unable to view the monitors.

The study’s results offer clues as to how various prenatal factors within a population are related to behavioral development in infants and children.

“Disorders of attention can impair the child’s ability to learn, so it is important to understand how these processes develop during the early period when infants are just beginning to explore their worlds visually,” Dannemiller said.