An Aymaran man gestures to the front as he talks about 'nayra timpu,' which literally means 'front time,' but refers to the past. ((Copyright Rafael Nunez/UC San Diego) )

South America's indigenous Aymara people have a reversed concept of time, with the past ahead and the future behind, an analysis of their language and gestures shows.

Until now, all studied cultures and languages in the world mapped the future in front and the past in back, said Rafael Nunez, a professor of cognitive science at the University of California, San Diego.

It's thought that people interpret time along a front-to-back axis with the future ahead and the past behind, given our frontal vision and how we move.

"The Aymara case is the first documented to depart from the standard model," Nunez said in a release.

"These findings suggest that cognition of such everyday abstractions as time is at least partly a cultural phenomenon."

The Aymara live in the Andes highlands of Bolivia, Peru, and Chile.

Nunez collected about 20 hours of videotaped conversations with 30 ethnic Aymara adults from northern Chile, focusing on discussions of past and future events.

Participants included those who speak only Aymara, only Spanish, or both. The majority of the population is bilingual.

Elderly Aymara who weren't versed in Spanish grammar tended to gesture in the opposite way to speakers of other languages.

To speak of the future, they thumbed or waved over their shoulder.

To indicate the past, they swept forward with their hands and arms, Nunez and Eve Sweetser, a professor of linguistics at UC Berkeley report inthe current issue of the journal Cognitive Science.

The pair don't know why elderly Aymara have a different approach. They speculate it may be because the people place such importance on whether an event or action was seen by the speaker.

If an Aymara speaker said, "In 1492, Columbus sailed the ocean blue," the sentence would need to specify if the speaker personally witnessed the event or was reporting hearsay.

When the evidence is so important, it makes sense to metaphorically place the known past in front, in the field of view, with the unknown and unknowable future behind your back, the researchers said.

There are about two millionto three million contemporary speakers of the Aymara language, but the rare linguistic pattern may become rarer as young bilingual speakers adopt the more common gestures, the researchers noted.