Ten-year Treasuries eased 2/32 in price to yield roughly 1.644 percent, up 1 basis point from late US trade. On Tuesday, the 10-year yield had touched a low near 1.615 percent, its lowest level in about three weeks.
Besides Bernanke's Friday speech at a symposium in Jackson Hole, Wyoming, investors are waiting for details on steps the European Central Bank is considering to ease the euro zone's debt crisis, and are also looking for more clarity on China's economic outlook, said a trader for a US brokerage in Tokyo.
Investors are likely to shift their asset allocation once they get more certainty on such issues in coming months and Treasuries could then see some sharp swings, the trader added.
"When we start to get that knowledge, then we can have some pretty high volatility. I would say we're kind of in the eye of the hurricane," he said.
Investors will be watching Bernanke's speech for hints on whether the Fed will announce another round of bond-buying after its policy meeting on Sept. 12-13.