Wall St. falls as healthcare, materials stumble

By Chuck Mikolajczak NEW YORK (Reuters) - Wall Street retreated on Wednesday, pulled lower by weakness in the materials and healthcare sectors as investors continued to weigh the possibility of an interest rate hike in the coming months. The market is awaiting Federal Reserve Chair Janet Yellen's speech in Jackson Hole, Wyoming, on Friday for insight on the direction of monetary policy. Recent hawkish comments from some Fed officials, including Vice Chairman Stanley Fischer, have raised expectat