That could hurt them, and the market as a whole.

Some individual investors clutched the money they had left after the market plunged more than 50 percent from October 2007 until March and stopped adding to stock funds. A recent study found about 6 percent stopped contributing to 401(k) plans altogether as they blamed workplace retirement savings plans, rather than the investments within the 401(k) plans, for losses.

"I am a middle-aged person, concerned about what approach is useful when it comes to socking away money for retirement," said investor Ruth Lipman. "My previous strategy of putting as much money into my IRA, 401(k), as possible no longer seems prudent."

Nonetheless, there are some signs that perhaps the fear is easing. When the Fidelity mutual fund firm dug through 11.2 million participant 401(k) accounts recently, researchers found that after three consecutive quarters of decreasing contributions, individuals increased them during the second quarter.

That might not be because of newfound confidence in the markets. It could be that with employment declining in the recession, people stopped saving for retirement temporarily while they paid down credit cards or set up emergency savings accounts and have begun to resume contributions.

The figures also could be skewed from a growing practice by employers to remove money from employee paychecks and automatically deposit it in workers' 401(k) accounts.

Pamela Hess, a researcher at Hewitt Associates, sees no evidence that people are anxious to invest in stock funds again.

"People pulled back from stocks dramatically [during the downturn], and we have not seen that reverse," she said.

She finds that surprising, because usually investors chase stocks as they rise. This time, she thinks investors are traumatized. Their behavior is following what has been documented in academic research: That people are more motivated to avoid large losses than to seek large gains.

That could have ramifications for individuals and the stock market. For investors who pulled away from stocks or from contributing to their 401(k) plans completely, the possibility of building up enough money for retirement is threatened.

Hess said many investors were too exposed to the stock market prior to the downturn and consequently lost large sums. When they did not add to stock investments in the downturn, they reduced their chance of rebuilding money they had lost.