Wall Street edges higher thanks to gain by Apple

The timing of future Fed rate hikes in the face of a sluggish economy is a major focus among stock investors who have benefited from historically low borrowing costs since the 2008 financial crisis. San Francisco Fed President John Williams and his St. Louis counterpart, James Bullard, both struck hawkish tones in separate appearances on Monday. Investors will listen for fresh clues to the Fed's intentions when Chair Janet Yellen speaks on Friday.