The Limits of Neuropsychological Tests of Executive Functions

Some neuropsychological tests traditionally have been labeled as "tests of executive function" (EF tests). These include the Wisconsin Card Sorting Test, the Stroop Color-Word Test, the Tower of London, the Rey-Osterrieth Complex Figure Test, the California Verbal Learning Test, and various computerized continuous-performance tests. Most of these tests were originally developed to assess patients with schizophrenia or those who had suffered damage to the frontal lobes of the brain. At first glance, such tests might appear to be appropriate measures to assess ADHD. In fact, they are not.

When given to children diagnosed with ADHD, such tests give variable results. Alysa Doyle and colleagues (2000) administered a battery of seven "EF tests" to a group of children diagnosed with ADHD. They found that no single EF test accurately differentiated children with ADHD from children without the disorder. Using all seven tests combined, they found that about 18 percent of the boys with ADHD appeared significantly impaired on at least four tests, while about 5 percent of the boys who did not have ADHD showed similar impairment. They concluded that "neuropsychological tests of attention and executive functioning underidentify cases that meet these [DSM-IV] criteria." Stephen Hinshaw and others (2002c) obtained comparable results from a neuropsychological evaluation of girls with ADHD.

Neuropsychological tests of executive-function impairments in adults are no better. Aaron Hervey and colleagues (2004) reviewed thirty-three published studies that used neuropsychological EF tests to evaluate adults with ADHD. He found that current neuropsychological measures are not sensitive enough to pick up ADHD symptoms.

Any who seek to identify executive function impairments of ADHD primarily by means of scores for these EF tests are likely to be frustrated because of the "lamppost problem." "Lamppost" here refers to the old story of the drunken man whose friends came along on a dark night and found him on his hands and knees crawling around under a streetlamp. When they asked what he was doing he explained, "I lost the keys to my car and I'm looking for them so I can drive home." They asked, "Where do you think you lost them?" "Somewhere over there in the dark across the street where my car is parked," he responded. "Then why are you looking here?" they asked. He answered, "It's easier to look here because the light's so much better!"

Executive-function tests might appear to be a convenient way to assess impairments associated with ADHD, but they don't shed enough light on the areas that need to be examined. Patrick Rabbitt (1997) explained why methods traditionally used by experimental psychology cannot validly be applied to executive functions. The usual scientific approach in research is to isolate and try to measure one variable that reflects one specific process and not others. He argued that this venerable strategy is entirely inappropriate for analyzing executive function because an essential property of all "executive function" is that, by its very nature, it involves the simultaneous management of a variety of different functional processes. (p. 14)

The usual "isolate the variable and test it" approach simply cannot encompass and measure the complex interactive nature of executive functions. Put another way, in seeking a new conductor for a symphony orchestra, one could not adequately evaluate candidates simply by having them rhythmically wave their arms or hum bars of a specific instrument's part in a section of a particular symphony. The ability to integrate and guide a large group of musicians through the performance of diverse musical pieces simply cannot be assessed with any isolated musical task. One would instead need to evaluate the candidate's ability to interact dynamically with the whole group of musicians as they play a variety of complex and challenging pieces.

Paul Burgess (1997) elaborated this same argument against trying to assess executive functions with simple tasks:

Goethe's famous comment that dissecting a fly and studying its parts will not tell you how it flies could almost have been intended for the neuropsychology of executive function . .. executive processing is called into play only when the activities of multiple components of the cognitive architecture must be coordinated. . . . Thus if a methodology is used where a task is broken down into its component parts, no deficit will be discovered in dysexecutive patients. (pp. 99-102)

A person's ability to perform the complex, self-managed tasks of everyday life provides a much better measure of his or her executive functioning than can neuropsychological tests. Tim Shallice and Paul Burgess (1991) demonstrated this fact in a study where patients with frontal lobe damage were unable to perform adequately everyday errands that require planning and multitasking, even though they achieved average or well-above-average scores on traditional neuropsychological tests of language, memory, perception, and "executive functions." Similar efforts to assess executive functions in more "real life" situations have been reported by

Nick Alderman and others (2003), who assessed adults doing tasks in a shopping mall, and by Vivienne Lawrence and colleagues (2002), who monitored children as they followed a series of directions during a trip to a zoo. These contrived situations are likely to be more useful than laboratory tests of executive functions, although they lack the flexibility and scope needed to assess adequately the wider range of executive-function impairments in real life.

What then is "the test" for differentiating ADD syndrome from normal inattention? There is no one test that can determine whether a given individual meets DSM-IV diagnostic criteria for ADHD. It is not like a fracture where a physician can look at an X-ray and definitively see that the bone is or is not broken. This is a diagnosis that depends on the judgment of a skilled clinician who knows what ADHD looks like and can differentiate it from other possible causes of impairment.

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