Wall Street falls after Fischer, Yellen comments

U.S. stocks were lower in a choppy session on Friday, with stocks bouncing between gains and losses as investors grappled with the possible timing of a U.S. interest rate hike after comments from Federal Reserve officials, including Chair Janet Yellen. The S&P 500 rose as much as 0.7 percent in the wake of a speech by Yellen in Jackson Hole, Wyoming that said the case for increasing interest rates had strengthened, but did not indicate when the Fed would raise rates. Stocks later reversed co