Moore and Johnson will report their findings in the Dec. 12 issue of the journal Psychological Science.
The psychologists tested 20 boys and 20 girls in the study, each 5 months old.
They used a common method in infant perception research: They had the infants look at something repeatedly until their amount of looking waned to less than half its original level. The researchers showed them a computer-generated image of a 3-D object that resembled an "L," constructed of multicolored cubes. Once the infants were bored with the object, the researchers showed them the same object from a different vantage point, and then the mirror image of the object.
"We're requiring the infants to rotate mentally in three dimensions," Johnson noted.
The 5-month-old boys looked at the mirror image about 1.5 seconds longer than they looked at the more familiar image, a "statistically robust difference" (although girls looked at both images longer than boys did), Moore and Johnson report. The 5-month-old girls looked at the mirror image for slightly less time than they looked at the familiar image.
The boys looked longer at the mirror image, the researchers said, because they recognized that the mirror image was completely new and that the other object was simply the original L-shaped image they had become bored with, shown from a different vantage point a task that required them to rotate the remembered original object mentally.
"We don't know why men are better than women at this task or why boys are better than girls at this, but we do now know that this difference extends all the way back to 5 months of age," Johnson said. "We have shown that this gender difference is present in a pre-verbal population, a population too young to have learned it from manual experience
|Contact: Stuart Wolpert|
University of California - Los Angeles