Boys may show spatial supremacy within a few months after birth; studies suggest gender gap emerges earlier than expected.

The gender gap in spatial abilities emerges within the first few months of life, years earlier than previously thought, psychologists report.

Males typically outperform females on spatial-ability tests by age 4, especially on tasks that require mental rotation of objects perceived as 3-D. Now two studies, which include 3- to 5-month-olds and are published in the November Psychological Science, conclude that a much greater proportion of baby boys than baby girls can distinguish a block arrangement from its mirror image, after having first seen the arrangement at a different angle.

The babies who did better on the test are presumed to have mentally rotated the original arrangement and recognized it at its new angle. They chose to gaze at the mirror image the second time around because they perceived it as new.

One investigation was conducted by David Moore of Pitzer College in Claremont, Calif., and Scott Johnson of the University of California, Los Angeles. The other was directed by Paul Quinn of the University of Delaware in Newark and Lynn Liben of Pennsylvania State University in University Park. Both groups suspect that sex differences in mental rotation develop shortly after birth because of an unknown mix of genetic, biological and environmental influences.

"The result we found was really somewhat of a shocker," Moore says. He had expected to demonstrate no sex difference in infants' mental rotation skills, laying the groundwork for pinpointing the age at which this spatial gap first appears.

"Simultaneous reports by two different labs using two different techniques are difficult to dismiss," remarks psychologist Nora Newcombe of Temple University in Philadelphia.

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Still, says Susan Levine of the University of Chicago, the new reports don't confirm that baby boys perform mental rotation tasks better than baby girls do. By 3 months, girls--but not boys--may notice changes in a block arrangement's orientation, Levine proposes. If so, girls would regard both a newly rotated block arrangement and its mirror image as novel, spending roughly equal amounts of time looking at both.