Wall Street slips in wake of comments by top Fed officials

U.S. stocks ended modestly lower after a volatile session on Friday, having bounced between gains and losses as investors wrestled with the likely timing of a U.S. interest rate hike following comments from top Federal Reserve officials. The S&P 500 rose after Fed Chair Janet Yellen said the case for raising rates had strengthened but did not indicate when the Fed would act. Stocks later traded lower after hawkish comments from Fed Vice Chair Stanley Fischer raised the possibility of a rate