ISTANBUL (AP) -- Kristi Castlin heard the starting gun, and then thought she heard it again.

The American was disqualified from her 60-meter hurdles heat Friday at the world indoor championships after stopping in her tracks as the rest of the pack took off toward the finish line.

Castlin cursed to herself as she walked off the track.

"I don't understand," she said.

In the Atakoy Arena, the starting pistol echoes off the walls, leading to much confusion throughout the night. Castlin, however, was one of two casualties, along with Jamaican rival Vonette Dixon.

Sally Pearson, the 100-meter hurdles world champion, won her heat in 7.85 seconds, but she also thought there was a problem at the start.

"I thought someone had false started. 'Oh crap, that wasn't me, was it?"' Pearson said. "But the girl next to me was starting so I just kept going myself. I don't know what they're going to do about that because it's really confusing."

The men running the 60 meters also heard the repetitions off the walls, but they had the advantage of running after the women.

"They taught us back there, don't listen for the echo. Go for the first sound you hear," said American sprinter Justin Gatlin, who won his heat in 6.64 seconds. "There is a little bit of inexperience by coming up and saying there is a false start next to me. Your job is to run, not to be an official."

There were four heats in the first round of the 60 hurdles, and Castlin ran in the second. She took a few strides and then stopped before jumping the first hurdle. Dixon went a little further before stepping off the track from the outside lane.

Nesta Carter, who also ran in the men's 60 a short time after the women vacated the center of the arena, said the problem needed to be resolved.

"You got to fix this gun," Carter said after advancing to the semifinals. "There's an unfair advantage because some people hear the gun before others and then it bounces back."

Jamaican team official Fitzalbert Coleman had a word with officials.

"When you try to speak to them, they say as far as they are concerned the system is fine," Coleman said. "The acoustics could be better."

The confusing reverberations seemed to bother just about everyone, but most learned from Castlin's mistake.

Sharona Bakker of the Netherlands, who qualified for the hurdles semifinals from the third heat, took a similar approach as Pearson - she just kept running.

"I was sitting in the blocks and I heard the noise on the blocks, but also in the area. So I heard two start calls," Bakker said. "So the girl next to me started, so I started also."

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