“Learning sign language is a really difficult thing to do,” says Cattani. “The students of sign language courses need to learn how to use the visual space to remember the signs.”

Cattani and her colleagues recruited 91 participants: 31 hearing nonsigners, 20 hearing signers, 18 deaf nonsigners and 22 deaf signers. They then showed the participants a slide with two drawings on it. Some of the drawings were of everyday objects, like a foot, and other drawings were five-sided shapes without standard geometric names. The pictures either appeared on the left side of the slide—feeding information to the participant’s right hemisphere—or the right side of the slide, targeting the participant’s left hemisphere. In all cases, the participants only had a fraction of a second to view the images.

Afterward, the participants looked at another slide and reported whether the two drawings were the same two they had seen before.

The four groups of participants were equally good at recalling whether they had seen the familiar object before, but the people who knew sign language performed better than the nonsigners at remembering the abstract shapes. And while the hearing and deaf signers were equally good at recalling abstract shapes, they seemed to tap different sides of their brains to perform the task—with hearing participants registering images more accurately in their left hemispheres—which is associated with language processing—and deaf participants favoring their right.

“It’s possible that the hearing participants used labels or linguistic strategies, like... attaching the name of an object similar to the abstract shape,” she says.

The study fits with Cattani’s own experience learning sign language. One of the most difficult parts, she says, was remembering the patterns her hands were supposed to trace in the air. And though her study doesn’t prove that signing sharpens abstract-shape memory, sign language teachers might want to consider using training exercises that target that skill.

—S. Dingfelder