When older people can no longer remember names at a cocktail party, they tend to think that their brainpower is declining. But a growing number of studies suggest that this assumption is often wrong.

Instead, the research finds, the aging brain is simply taking in more data and trying to sift through a clutter of information, often to its long-term benefit.

The studies are analyzed in a new edition of a neurology book, “Progress in Brain Research.”

Some brains do deteriorate with age. Alzheimer’s disease, for example, strikes 13 percent of Americans 65 and older. But for most aging adults, the authors say, much of what occurs is a gradually widening focus of attention that makes it more difficult to latch onto just one fact, like a name or a telephone number. Although that can be frustrating, it is often useful.

“It may be that distractibility is not, in fact, a bad thing,” said Shelley H. Carson, a psychology researcher at Harvard whose work was cited in the book. “It may increase the amount of information available to the conscious mind.”