Feature

Many of the tests used in research to demonstrate age-related decline in executive functioning--processes thought to control other cognitive operations--may not go far enough in differentiating these control functions from other processes, say psychologist Timothy Salthouse, PhD, and colleagues at the University of Virginia, in a study published in this month's Journal of Experimental Psychology: General (Vol. 132, No. 4).

Salthouse and his team examined the possibility that executive function may overlap with other cognitive abilities in test results, therefore challenging established test methods, including the Wisconsin Card Sorting Test, Verbal and Figural Fluency Test and Trail Making Test--all used to demonstrate how executive function can deteriorate.

Researchers have used the concept of executive functioning in recent years to account for cognitive decline in older adults, says study co-author and psychology graduate student Diane Berish. This makes a lot of sense, she adds, because disruption of central control processes can result in impaired behavior even if component processes such as memory and attention are intact. However, the research done by Salthouse's team suggests that people who differ on these tests of executive functioning differ in nearly the same manner on tests commonly used to assess inductive reasoning and fluid intelligence.

Using several widely implemented tests to gauge cognitive ability in 261 men and women between 18 and 84 years old, the researchers found that age-related effects on individual cognitive processes decreased when they statistically controlled for measures of executive function, Berish says. In other words, when the researchers took into account people's executive function abilities, the differences in cognitive functioning associated with aging were much smaller.

However, there was only weak evidence that the way executive function was being measured excluded other processes, she added. That means that declines attributed to failing executive function may include some component of other cognitive failures. For example, she said, slowing in an older adult is a result of failing executive function and another factor like sequence-keeping or memory. Frequently used tests have not sufficiently separated the two to get accurate measures of each, placing too much emphasis on the role of executive function, she added.

In particular, they found that measures of working memory, attentional capacity and inhibition overlapped with measures of executive function. That finding means that traditional tests of memory, attention and inhibition are somewhat less reliable than previously thought and require broader research into what causes individual differences in cognitive abilities, Berish says.

"What we're trying to do is perhaps encourage people to use caution in making claims about causation, because they haven't established the precursor to make sure their tests are actually testing executive functioning," she says.

The results of this research do not invalidate ways that executive functioning has been identified in the past, Berish says, but the study does suggest that researchers investigating cognitive and neuropsychological constructs should recognize that they are probably studying only one aspect of a larger phenomenon.

"It's a cautionary tale, not to invalidate research in the past, but perhaps to remind researchers that analytic procedures are available to investigate the possible correspondence between constructs used in different areas," Berish adds.