About Attention

Attention Deficit Disorders and the Test of Variables of Attention (T.O.V.A.®)

Lawrence M. Greenberg, MD
Professor Emeritus of Psychiatry
University of Minnesota
Author of the T.O.V.A.

Please note that the following information contains the expressed opinions and conclusions of the author and is not intended as, nor may it be used as, medical advice. This information should not replace the clinical decisions of a licensed professional based on personal examination. The author shall have no responsibility for the use or misuse of this information.


Attention deficit disorders (ADD) is a descriptive term used by professionals to indicate that a child or an adult has a significant problem maintaining attention (that is, staying on task) when it is reasonable to expect them to be able to do so. There are many causes of inattention, ranging from boredom to neurological (including ADHD) and psychological problems. (See 3 below).

Attention Deficit Hyperactivity Disorder (ADHD) is the diagnosis currently used by clinicians to indicate a neurological disorder with three prominent clusters or groupings of problems that can occur separately or together:

  1. inattention and distractibility;
  2. hyperactivity and impulsivity ("disinhibition");
  3. disorganization or problems of "executive functioning"

In this review, the descriptive term, ADD, refers to the presence of one or more of these symptoms, regardless of diagnosis. The diagnostic term, ADHD, refers to the neurological disorder as described in the Diagnostic and Statistical Manual (DSM IV) that is currently used by clinicians. The symptoms of ADHD are grouped into four diagnostic categories based on the manifested symptoms: Inattentive Type, Hyperactive Type, Mixed Type, and Other.

Note: The diagnostic terms and the descriptive symptoms change with each new DSM as we learn more about the disorder. As an example, ADHD was previously called the Hyperkinetic Reaction of Childhood before we knew that only half of the children with ADHD are hyperactive, and that 5% of adults have ADHD.

This review focuses on the specific symptoms of ADHD (and ADD) that are "targeted" for treatment:

Inattention and distractibility

In ADHD, the brain often processes information too slowly and too quickly (that is, inconsistently) compared to persons who don't have ADHD. Persons with ADHD have difficulty staying on task and tend to be easily distracted and disorganized. Of course, they can and do compensate somewhat. However, as they get older, the information to be processed gets more complicated, there's a sequence of things to do rather just a few things at a time. Some children do fine until "show and tell" is replaced by primarily verbal or written instructions or material, especially in the mid-grade school years. Others do all right, even if they do work longer and harder than their peers, until high school, or, in some cases, until college when they just can't keep up with the others.

Even if the person is "hyperactive" and impulsive (see below) as well as inattentive, the brain processes information inconsistently. It's counterintuitive. We'd expect that a hyperactive person processes information too fast to keep things straight. However, the person with ADHD sometimes processes too slowly and responds with confusion, frustration, and a sense of failure because they can't understand the message or respond appropriately.

Half of the children with ADHD simply process information inconsistently, but they aren't hyperactive. Adults with ADHD aren't usually hyperactive even if they were as children- they "outgrow" the hyperactivity component although they often remain physically and/or verbally impulsive. Since children are usually referred to a clinician because they are disruptive and/or disrupted, children who are inattentive but not hyperactive are usually not referred and, instead, are thought to be uninterested, noncompliant, easily bored, or maybe even not too smart. These children often don't get to a clinician, and don't get diagnosed. Instead, they often end up with low self-esteem, being oppositional, and/or favor activities that hold their attention.

Case illustration: A medical student asked for a clinical consultation after hearing a lecture on adult ADHD. He'd been diagnosed as a child as having dyslexia (a reading problem) and received special educational services. He did all right in school but had to study much more than his peers, especially in high school and college. Since reading was a problem, reading assignments and tests were particularly difficult for him. He devised all sorts of coping strategies like taking frequent short breaks, and studying at night when it was quiet. He assumed that he was of average ability and attributed his academic progress to working so hard. The clinical assessment revealed that he had the inattentive type of ADHD. There was no evidence of dyslexia (although he may very well have had it as a youngster), and he was actually much smarter than he thought. He responded very well to medication (see 13, below), and is now a successful physician.

Hyperactivity and impulsivity

Persons with ADHD who are hyperactive (that is, overactive) and/or impulsive do not successfully control their behavior (leading to impulsivity and related problems) and/or do not modulate activity level (leading to hyperactivity). It’s like their "brakes" don’t work well- they have difficulty stopping and thinking before they act. They might be physically and/or verbally overactive.

As noted above, these are the children who are referred to a clinician because their behavior bothers others- they can be irritable, aggressive, destructive, and just downright obnoxious. Some are just all over the place- they can't sit or stand still for very long. And some are all of the above.

Case illustration: His parents have always had difficulty managing Bobby's behavior. As an infant and a baby, he was difficult to settle down with frequently interrupted sleep, colic, and irritability. As a toddler, he was into everything- running into the street, breaking things, and still very irritable. Within days of starting preschool, after his teachers recommended that he be evaluated, it was determined that he had the mixed type of ADHD (both inattentive/distractible and hyperactive/impulsive). He responded nicely to medication (see 13, below), short term individual counseling, and parental consultations to help them manage his behavior more effectively and consistently.

Over half of the children with either type of ADHD grow up to be adults with ADHD. If the diagnosis of ADHD (with or without hyperactivity) was missed in childhood, and the person did not "outgrow" the processing problem in the teen years, they can end up with complications of untreated ADHD, including low self-esteem/depression, obsessive-compulsive traits, excessive anxiety ("fear of failure"), antisocial traits, and/or substance abuse, using cocaine, alcohol, methamphetamine, marijuana, and excessive sleep medications. Individuals with untreated ADHD also tend to unconsciously self medicate with excessive amounts of caffeine and nicotine. (Both caffeine and nicotine are psychostimulants. They stimulate the brain. However, they are also very addicting and have some very nasty side effects.)

Disorganization (problems of "executive functioning")

Persons with ADHD often have difficulty "putting it all together". Sequential information is somehow all mixed up or lost when recorded in short term memory. When the person tries to retrieve the information from short-term memory, some of the data are missing and some of the data don't make sense, making it difficult to respond appropriately and correctly assess the results. The person has difficulty organizing themselves- projects are begun and abandoned unfinished. Sometimes their sentences make sense, but their paragraphs don't, literally and figuratively.

It helps to be intelligent, and to be able to cope better than others, but people with executive functioning problems can't perform up to their ability even when working much harder than others. Frustrated, they try harder and/or give up.

Case illustration: A very successful scientist with a Ph.D. was promoted from a research position to manager of his section. Within days, he was overwhelmed by details and unable to keep organized. He'd always been a hard worker- even in school he studied far more than his peers and obtained good grades. A clinical evaluation revealed a very high IQ and inattentive type of ADHD with prominent executive functioning problems. Fortunately, he responded very well to coaching (focused on acquiring organizational skills and reducing distractions) and to medication (see 12 and 13, below).

The Cause(s) of Attention Disorders

The term, ADHD, is really a misnomer. It's not really a disorder. By definition, a disorder has certain characteristic symptoms (signs and behaviors that are "abnormal"), a predictable natural history (what happens over time without treatment), and a common underlying cause ("etiology"). Treatment, if any, is directed to modify the symptoms or alter the underlying cause of the disorder.

Instead, ADHD is a symptom complex, and the diagnosis is based on the presence of a sufficient number and severity of the symptoms that are listed in the current diagnostic handbook (DSM IV) that clinicians use. However, this exact complex of symptoms has many very different causes (etiologies) that have different natural histories, and respond to very different treatments.

There are many possible causes of attention problems, including:

a) it's normal, age appropriate behavior that is mislabeled; most of the overly active, difficult-to-manage children don't have ADHD;

Case illustration: Sue was a very intelligent, active, intrusive, and somewhat "bossy" six years old girl who was a "management" problem at home and in school. She always wanted to do it herself and didn’t "listen well". Her parents tended to be inconsistent in their behavior management attempts and to be easily irritated by her. Her teacher was boringly repetitive and pedantic. Sue didn’t have ADHD- she was what Linda Budd called "active alert". Perfectly normal. Things improved considerably with some behavior management counseling for the parents and consultation with the teacher.

Note: Linda Budd’s books on the active alert child are very, very helpful even if the child does have ADHD.

b) any number of general medical problems (such as anemia, hyperthyroidism, chronic ear infections, and dietary inclusions/sensitivities;

Clinical comment: Dietary sensitivities do exist although they are not very common. One of our studies done some years ago revealed that only one of twenty children whose ADHD symptoms reportedly "responded" to dietary management did, indeed, respond sufficiently to changes of diet.

c) many medications (such as anticonvulsants, antihistamines, and psychodepressants that sedate or slow the brain);

Comment: Since these medications are often necessary for the general well being of the person, it’s important to use the lowest effective dose to minimize side effects.

d) toxic conditions (drug induced or an illness);

e) sensory deficits (like undetected hearing and visual impairments) and sensory hypersensitivities;

Comment: The clinician needs to consider all of these potential problems when evaluating attention.

f) neurological problems other than ADHD, such as visual and/or auditory distractibility, sleep disturbances (including narcolepsy), epilepsy, "acquired/traumatic" or Traumatic Brain Injury (TBI);

Case illustration: A successful professional was seriously injured in an auto accident in which close relatives were killed. He was evaluated by teams of professionals, and, although he'd had a severe concussion, there was no sign of brain damage or memory impairment. His recovery was slow but steady with many surgeries, medications, and rehabilitation interventions. Several years later, he was telling a friend, a psychologist, that in spite of grief counseling, he remained "depressed"- he felt preoccupied and was distractible, frequently off task, disorganized, and easily bored. These are symptoms of depression, and they are also symptoms of ADHD, inattentive type. When his friend referred him for an ADHD assessment, it was discovered that the evaluation obtained after the accident did not include a T.O.V.A. even though brain injuries can cause ADHD. It turned out that he did have traumatic ADHD, and his symptoms responded to treatment.

g) family style and (dis)organization (including social and cultural factors);

h) lack of school readiness, different learning style, and low motivation;

Comment: Some individuals learn best with a "hands on" experience rather than hearing or reading about it.

i) stress (including emotional trauma and inappropriate demands);

j) intellectual impairment and precocity;

k) learning disabilities;

l) other psychiatric conditions including abuse/post traumatic stress disorder, psychosis, bipolar or obsessive-compulsive disorders, autism, Tourette, depression, and anxiety;

Comment: A multi-faceted clinical evaluation is needed to determine whether one or more of these conditions exist with or without ADHD.

m) substance use, abuse, and withdrawal (including caffeine and nicotine);

Comment: Substance use and abuse are common in untreated individuals with ADHD, and the co-existence of ADHD makes the treatment of substance abuse more difficult. Although it seems counterintuitive to treat a substrance abuser with ADHD with low doses of psychostimulants (See 13 below), it’s the most effective treatment.

n) behavior disorder including oppositional/defiant;

Case illustration: Jack was six years old when seen by his family physician because of hyperactivity, impulsivity, stealing, and temper tantrums at home and at school where he was not progressing academically. Assuming that Jack had ADHD, combined type, the doctor prescribed 10 mg of methylphenidate (a psychostimulant). Jack initially appeared to be less hyperactive and impulsive. The dosage was increased to 20 mg with minimal improvement and some increase in irritability and sleep disturbance. Jack was subsequently seen for a psychological evaluation and was diagnosed and successfully treated for a behavior (conduct) disorder without medication.

o) and, finally, the neurological disorder of attention or ADHD

To complicate matters even further- these causes are not mutually exclusive. An individual with the ADHD symptom complex could very well have more that one cause co-existing (co-morbidity) and needing more than one treatment modality. Prime examples would low self-esteem and depression. In addition, there can be a genetic component as well since a percentage of individuals with ADHD have close relatives with it also.

Sometimes co-morbid problems, like low self-esteem, are so prominent that the clinician may not recognize the underlying attention disorder. This is often the case in children with the Inattentive Type of ADHD and in adults when ADHD wasn't diagnosed in childhood.

So, it's very important that the clinician carefully considers all of the possible causes of the symptom complex without leaping to a conclusion and prescribing a treatment. Selecting a diagnostician is not an easy task- you want someone who has the necessary expertise. An excellent source of information is The TOVA Company that maintains an up to date directory of clinicians who specialize in the diagnosis and treatment of attention disorders, including ADHD. For free recommendations of clinicians in a particular geographical area, please call 1.800.REF.TOVA (800.733.8082).

The Incidence (Frequency of Occurrence) of ADHD

The symptom complex of ADHD occurs in 7-8% of children and 5% of adults. The number of ADHD diagnoses is definitely increasing, in part reflecting the increased awareness by the general public and professionals alike. Some of the increase is due to assuming that every overly active youngster has ADHD. (See 3 above.) Some of the increase reflects the increasing number of brain injuries from accidents, etc.

While we used to think that there were many more males than females with ADHD, we now know that females tend to have the inattentive type of ADHD and are often missed because they're not bothering any one. The same was true for adults- we used to think that all of the children with ADHD "outgrew" it by the mid-teen years. Now we know that only half of them do although the hyperactivity component generally does drop out.

Diagnosing ADHD is not an easy process. Perhaps a third of the children referred to us with the diagnosis of ADHD (and sometimes being treated as having ADHD) don't have ADHD. They have the symptom complex but not ADHD. On the other hand, there are at least as many undiagnosed children and adults who have ADHD (especially the inattentive type).

The T.O.V.A. visual and auditory tests

The T.O.V.A. is a computerized continuous performance test (CPT) that is used to assess attention and impulsivity.

There are two types of T.O.V.A. test: the visual test measures visual information processing, and the auditory measures auditory information processing. Designed like computer games, both T.O.V.A. tests are easy to administer to children (age four and older) as well as adults.

The visual T.O.V.A. uses two simple geometric figures to measure attention, and the auditory uses two tones. Unlike other CPTs, the T.O.V.A. avoids the confounding effects of language, cultural differences, learning problems, memory, and processing complex sequences. The visual test target is a square with a second but smaller square inside of it, near the upper border. The nontarget is a square with the smaller square near the lower border. The auditory test uses two easily discriminated notes. The high note is the target, and the low note is the nontarget. That’s it- no complicated sequences of numbers or letters, no confusing colors or sounds. A target or a nontarget randomly flashes on the screen or is sounded every two seconds for a tenth of a second (100 msecs). The instructions are to press a specially designed, accurate microswitch as fast as you can every time a target appears or is heard, but not to press the microswitch when a nontarget appears or is heard. It’s important to be fast but not too fast- it’s just as important to avoid pressing the microswitch when it's a nontarget. It’s that simple.

Well, it actually isn’t that simple. The targets and nontargets are presented in two different patterns. In the first half of the test, the target randomly occurs once for every 3.5 nontargets. So the first half of the test is called the infrequent (target) condition. With the visual test you really have to focus on the screen, or you’ll miss the occasional target. With the auditory test, you have to listen carefully, or you'll miss the occasional high note. The excitement (if there is any) wears off very quickly for the first half of the test is 10.8 minutes long. It gets very boring very soon, and that’s what we want- a measure of attention in a boring task.

The second half of the test is also 10.8 minutes long, and now the target occurs 3.5 times to every one random nontarget. So it’s called the frequent (target or response) condition. In contrast to the first half, you’re pressing the microswitch most of the time, and every once in a while you have to inhibit the natural tendency to respond because a random nontarget occurs. This half is more exciting than the first half and provides a measure of attention in a stimulating task.

Why do we need visual and auditory versions of the T.O.V.A.? Most people are "concordant" for both visual and auditory information processing. That is, they visually and aurally process information similarly whether it be slowly, quickly or in between. However, a significant number (estimated at 12%) of individuals are "discordant" and process visual and auditory information differently. That is, they may be significantly slower in one than in the other modality. So we need to test both visual and auditory processing.

Variables Measured by the T.O.V.A.

a) The consistency of the response times is called Response Time Variability and is measured in milliseconds. Response Time Variability is the most important measure of the T.O.V.A. and tells us how consistent (or inconsistent) a person's Response Time is.

b) The time it takes to respond to a target is called Response Time and is measured in milliseconds. This measure tells how fast (or slow) a person processes information and responds by pressing the microswitch.

c) d' (d prime) is derived from Signal Detection Theory and measures how quickly one’s performance worsens ( deteriorates ) over the 21.6 minutes of testing.

d) When someone responds to the nontarget, it is called a Commission Error, a measure of impulsivity (also called disinhibition).

e) When someone does not respond to the target, it is called an Omission Error, a measure of inattention.

f) Post-Commission Response Times measure how much faster or slower a person becomes after mistakenly responding to a nontarget. This measure helps us to identify one of the other causes (like conduct disorder) of the symptom complex.

g) Multiple Responses are the number of times a person presses the microswitch more than once a target. This measure helps us to identify other neurological conditions.

h) Anticipatory Responses measure how often a person presses the microswitch so quickly (<150 msec) that they’re probably guessing rather then waiting longer and being sure.

The T.O.V.A. Microswitch

In contrast to other commercially available CPTs that use the computer keyboard or mouse to record responses, the T.O.V.A. uses a microswitch. Since Response Time Variability and Response Time are two very important measures, we need to measure time very accurately to determine how fast and inconsistent Response Times are.

Why a microswitch? To obtain very accurate time measurements (±1 msec). Computer keyboards and mouses, are not as reliable and can vary significantly (±28 msec). In addition, if you use a different computer with a different measurement error to retest someone, it's very difficult to compare the results.


Once testing is completed (21.6 minutes long for 6 years old and older and 10.8 minutes for 4 and 5 years old), the results are immediately analyzed, and the complete interpretation and graphics are available on the monitor and to be printed out.

The T.O.V.A. report compares the test results with the results of a large number of people who do not have an attention problem. The test results are interpreted and reported as within the normal expectable range or not.

As the brain matures and changes, it processes information faster and more accurately from childhood to the late teen years/early twenties, remains pretty steady until the early- to mid-sixties when it slows somewhat. (So it is accurate to say that younger adults are faster than older ones, but older ones can compensate by exercising better judgment.) It's also true that males and females process information differently.

Thus, age and gender make a difference. For instance, when comparing individuals without ADHD, eight year old boys perform differently than eight year old girls and differently than nine year old boys.