Wall Street flat, with all eyes on Fed

Wall Street was little changed on Wednesday morning as investors played a waiting game ahead of Federal Reserve Chair Janet Yellen's speech on Friday for clues on the timing of an interest rate hike. Yellen's keynote speech will be the main focus of a meeting of global central bankers in Jackson Hole, Wyoming. The meet, which starts Thursday, has traditionally been used by Fed chiefs as a platform to signal the direction of monetary policy.