Wall Street shares closed flat on Wednesday trading session as investors awaited for big moves before today's speech of the U.S. Federal Reserve Chairwoman Janet Yellen, however, retailers' stocks advanced for the second straight day. The Standard & Poor's 500 Index gained 0.04% to 1,845.16, the Dow Jones industrial average added 0.12% to 16,198.41 and the Nasdaq Composite index rose 0.10% to 4,292.064.