NEW YORK ( -- A recent survey by BlackRock observes that only 18% of respondents' investable assets are currently deployed in stocks. For those investors, cash, at 48% of financial assets, remains the largest holding.

That many individual investors remain "underexposed" to equities is sometimes cited as a heartening sign. The bull market, notwithstanding its nearly five-year-long duration, doesn't appear to have "bubble-like" dimensions, based on certain measures of investor participation.

Some of this "equity-light" allocation behavior reflects the preferences of older investors, who own a disproportionate share of U.S. stock market wealth. In fact, those born before 1965 account for 32% of the population, but represent 68% of all stock and bond investors.

So why does the 50-plus crowd remain skittish about owning stocks, five years after the 2008 financial crisis, and in the immediate wake of a cheer-worthy 28% year-to-date gain in the SPDR S&P 500 ( SPY - Get Report)? Are the fears of older investors more readily aroused by memories of the financial crisis and bear market?

The most obvious explanation for the risk aversion of older individuals is that they're closer to retirement age, and therefore reluctant to retain a high exposure to equities. Should another market meltdown occur, those in, or approaching, retirement would have less time to recover their losses.

However, there may be another factor at play. For older investors, memories of the 2008 financial crisis may loom larger, partly because they "feel" like they occurred relatively recently, compared to the perceptions of younger adults.

There are reasons for this disparity in time perception. Apparently, perceived time moves faster as individuals grow older. For someone over age fifty, the events of four or five years ago "feel" more recent than might be the case for someone in their 20s.

This phenomenon is known as "time compression." According to a recent academic paper, "a person's perceived duration of an interval understates its true duration, so for example, one calendar year may seem to pass in just a few months. A commonly expressed feature of time compression is that it tends to worsen with age; life speeds up as you get older."

The academic report also explains the dynamic of time compression in mathematical terms: "Exogenous time compression is normalized to unity at age twenty-five and declines with the square root of age."

As an example, consider that this week marks the 50th anniversary of the assassination of President Kennedy. Others may share my perception -- particularly if they're middle-aged or older -- that memories of events leading up to, or immediately following, that tragic day seem to recede into the distant past.

At the same time, political and cultural milestones of the 1980s and 1990s might feel as though they had occurred more recently than is actually the case. In other words, our memories of events and images associated with earlier periods in time are not distributed linearly.

The older one is, the more recent the events of the great financial crisis might feel. Younger people may be better prepared to dismiss the last bear market as a "thing of the past." That may not be the only explanation for why older investors remain leery of the stock market, but it's one worth considering.

At the time of publication the author had no position in any of the stocks mentioned.

This article was written by an independent contributor, separate from TheStreet's regular news coverage.

Brian Egger is the founder, publisher and gaming and travel analyst of During the last twenty years, he has held positions of increasing responsibility as a gaming, lodging and travel analyst at Goldman Sachs, Donaldson Lufkin Jenrette, Credit Suisse, BMO Capital Markets and Topeka Capital Markets. He also served as Associate Director of Research at BMO and Director of Research at the Institutional Research Group. Brian has held four team positions, including two second-place rankings, in Institutional Investor's Gaming, Lodging and Leisure categories. He has also been recognized as a six-time Wall Street Journal "Best on the Street" analyst. Brian taught securities analysis to MBA students as an Adjunct Professor in the Finance department of Columbia Business School. He received a BSE from the Wharton School of the University of Pennsylvania and an MBA from the University of Chicago Booth School of Business.