WASHINGTON (AP) — Pedestrians walking along sidewalk in the nation's capital Thursday found themselves with a choice.

"No cellphones," said lettering on one side of the sidewalk. "Cellphones," the other lane said. "Walk at your own risk."

The walkway warnings, which ran about a block on Washington's 18th Street, weren't the work of city officials. Instead, they were put there by the brains behind a National Geographic television show as part of a behavior experiment.

A National Geographic Channel spokesman acknowledged the channel was behind the temporary signage and said pedestrians' reactions were being filmed for "Mind Over Masses," a new series. But the spokesman, Chad Sandhas, declined to discuss details of the experiment during the filming, which he said would continue Friday.

A notice on the website of the city's Office of Motion Picture and Television Development said the new science series "uses what we know about human behavior" to develop "interactive solutions to everyday problems." The notice said the show planned to create "Fast and slow lanes" on the sidewalk, "allowing participants to choose."

On Thursday afternoon, many pedestrians seemed to ignore the markings, though there were some who took pictures of the novel signage or stopped to watch someone in a gorilla suit eating a banana that was also somehow part of the filming.

Irene Fadakar, 54, a secretary who walking, said she noticed the markings at the beginning of the sidewalk. But she acknowledged that less than a block later she was back on her phone, walking in the lane marked no cellphones.

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