Men’s spatial superiority takes cultural cues

Disputed study puts social forces at root of sex disparity

August 29, 2011 at 2:53 pm

Culture may hold a spatial place in thought. Social forces profoundly influence people’s ability to think about three-dimensional objects, a new study suggests.

CULTURAL EQUALITY In a new study, Khasi villagers in Northeast India displayed no sex differences in spatial ability. Researchers suspect that Khasi culture, which is organized around females, largely erased men’s spatial superiority observed in many other societies. M. Hoffman et al/PNAS 2011

PIECES OF MIND Villagers who assembled a four-piece horse puzzle have provided clues to cultural forces at the root of men’s and women’s spatial skills. M. Hoffman et al/PNAS 2011

In tests of spatial ability, men traditionally outperform women. But men’s spatial superiority disappears among Northeast India’s Khasi villagers, say economist Moshe Hoffman of the University of California, San Diego and his colleagues. In Khasi society, youngest daughters inherit property, men forward earnings to wives or sisters, and females get as much schooling as males.

Among neighboring Karbi villagers, men display spatial-thinking advantages over women, similar to those in many Western societies, Hoffman’s team reports in an upcoming Proceedings of the National Academy of Sciences. In Karbi society, males inherit and own land and receive more education than females.

“These results show that nurture plays an important role in the gender gap in spatial abilities,” Hoffman says.

But some researchers who study sex differences in thinking view the study skeptically.

It’s not clear that the study in fact measured spatial ability, remarks psychologist Richard Lippa of California State University, Fullerton. Hoffman and colleagues measured spatial ability as the time taken to solve a four-piece jigsaw puzzle. But they didn’t assess volunteers’ accuracy at mentally rotating 3D figures and performing other spatial tasks, Lippa notes.

The villagers’ puzzle-assembly time could reflect cautiousness, impulsiveness or a desire to please the researchers, not spatial ability, Lippa says.

Psychologist Diane Halpern of Claremont McKenna College in California agrees. “This new paper doesn’t tell us much about sex differences in spatial cognition.”

In Hoffman’s study, 1,279 Khasi and Karbi villagers received the equivalent of 25 percent of a day’s wage to solve a jigsaw puzzle of a horse. Standard spatial tests are too abstract for these villagers, but the horse puzzle requires mental rotation of picture fragments, Hoffman says.

Khasi men and women alike took an average of just over 30 seconds to put together the puzzle. Karbi men required an average of 42 seconds, versus 57 seconds for Karbi women.

Although better-educated villagers solved the puzzle faster, schooling leaves much of the group difference unexplained, the researchers say.

Findings from these Indian villagers miss the big picture of how sex differences in spatial thinking vary across nations, Lippa asserts. In a 2010 study, his group examined the scores of more than 200,000 people in 53 countries on tests of mental rotation and line-angle judgments.

Surprisingly, men’s spatial advantage was largest in rich countries with many educational and career opportunities for women. Spatial scores for both sexes declined to roughly equal levels in poor countries, in line with a previous study of poor families (SN: 11/19/05, p. 323).

Lippa’s study compared nations that differ in many respects, including culture, genetics and means of subsistence, Hoffman responds. The new study compares two societies identical on all dimensions except culture, he argues, allowing a conclusion that nurture affects sex differences in spatial ability.