IT'S THE ECONOMY: For every hint Wednesday that the economy is improving, there was another sign that it isn't. Chrysler, Volkswagen and Nissan reported strong sales in July, but General Motors and Ford faltered. Construction spending rose, but manufacturing activity fell.

TECHNICAL DIFFICULTIES: The opening minutes of trading were chaotic for some companies, with their shares swinging wildly for no immediately apparent reason. The culprit turned out to be a technical problem at Knight Capital, one of the largest processors of stock trades.

WHAT'S BERNANKE THINKING: Stocks turned down after the Federal Reserve wrapped up its two-day policy meeting with a statement that disappointed investors. Policy makers said the economy is weakening, but they also avoided taking new action to try to fix it.