Mary Schapiro said some of the five commissioners wanted to discuss trading strategies and new technologies face-to-face with those in the industry, now that the SEC has received scores of public comments on its 74-page paper, known as a concept release.

Under some political pressure, the SEC is probing whether the high-tech, high-speed equity marketplace now dominated by computer-driven trading is fair for long-term and less-sophisticated investors. It received some 115 letters before last week's deadline.

"Why now? Because we owe it to the public to start to examine and scrutinize these issues," Schapiro said at the Reuters Global Financial Regulation Summit in Washington D.C.

"This isn't a quick turnaround," she said of the review, adding that "very thoughtful" letters have arrived and that the SEC also expects to review academic studies.

Any changes could revamp the flow of trading in the electronic marketplace, which has transformed in the last decade. High-frequency trading, in which lightning-fast algorithms are used to make markets and capitalize on tiny imbalances, accounts for an estimated 60 percent of all U.S. stock trading.