The market has recorded three of the four lowest-turnover full...

The market has recorded three of the four lowest-turnover full sessions of 2012 this week. The low volume reflects investors' reluctance to place big bets before Bernanke's speech, and could weigh on profits at exchanges and brokers.

Equity price movements have been muted as well, with the S&P hardly moving over the past three days. It hasn't closed with a 1 percent move in either direction since August 3.

Bernanke addresses a conference of central bankers in Jackson Hole, Wyoming, on Friday, where he could announce new measures to boost growth. He is expected to stoke expectations for a third round of quantitative easing, though he may not detail the timing of the Fed's action.