Attacking the Validity of Field Sobriety Tests

As discussed under DUI Stop and Arrest, part of the combination of factors that officers use to arrest you is your alleged performance on so-called field sobriety tests. The concept behind a field sobriety test involves testing either the suspect’s alleged physical reaction to alcohol, such as with the Horizontal Gaze Nystagmus Test, or creating a set of tasks which will allow the officer to look for alleged indicators of alcohol intoxication. These indicators may include the suspect’s ability to understand and follow instructions, estimate time, control his body movements, perceive and react to the world around him, and speak clearly. The tests must be simple and an average person must have no difficulty performing the tests when sober. Furthermore, each test must be thoroughly explained and demonstrated in such a manner that the suspect understands what is expected. Beyond that, the tests rely totally on the officer’s ability to perform them exactly as required by the National Highway Traffic Safety Administration and on the officer’s ability to interpret the test results, often at the same time as he is administering the test itself.

As the officer administers these field sobriety tests to you, he also evaluates your performance with an eye for certain “clues” which he is taught are indicators of either excessive blood alcohol level or state of intoxication. Most officers are instructed by training materials from the National Highway Traffic Safety Administration, which has established a set number of standardized field sobriety tests and specifically instructed officers in how to administer and interpret those tests. There are three standardized field sobriety tests in use by law enforcement: the Horizontal Gaze Nystagmus Test, the Walk and Turn Test, and the One Leg Stand test. There are also alternative field sobriety tests that, while not accepted as part of the standard three test battery, are nevertheless viewed by law enforcement as scientific and accurate indicators of excessive blood alcohol level. Typically, five alternative field sobriety tests are also accepted as allegedly reliable indicators of a driver’s state of intoxication. These include the Rhomberg Balance Test, the Finger to Nose Touch Test, the Hand Pat Test, the Finger Count Test, and the Verbal or Written Alphabet Test.

Law enforcement officers are generally advised that officers should not rely on any one test as the sole criteria for making a DUI arrest. It is emphasized that an officer must base his or her opinion as to whether a suspect is driving while intoxicated or with a blood alcohol level in excess of the legal limit on the totality of the circumstances presented. According to the National Highway Traffic Safety Administration, the presence of a set number of “clues” identified based on the suspect’s performance on these field sobriety tests is a reliable indicator of a likely blood alcohol level of at least .10.

Although NHTSA training materials claim that an exact blood alcohol level can be predicted based on performance on “tests” such as the Horizontal Gaze Nystagmus Test, that information is not admissible in court. All that the officer will be able to indicate in court is that the nystagmus test provides evidence to support any opinion he reached as to the subject’s state of “intoxication”. Because the officers are trained to believe in the validity of these tests as reliable investigatory tools in their DUI investigation, any perceived deficiency in a suspect’s performance will carry great weight in the officer’s mind as he decides whether he believes there is enough evidence to arrest you.

The crucial issue in the area of field sobriety tests is whether the test was administered and interpreted in accordance with the National Highway Traffic Safety Administration (NHTSA) guidelines for the test. One study observed that the field sobriety tests were administered in the field incorrectly over 90% of the time. As the National Highway Traffic Safety Administration manual itself advises, the standardized field sobriety tests are not flexible. They must be administered each time exactly as outlined and officers administering the tests are not to deviate from the instructions in any way. The manual goes on to advise that these test results are only to be considered valid indicators of blood alcohol level or state of intoxication if:
• they are administered in the prescribed, standardized manner in exact compliance with NHTSA guidelines;
• the standardized clues are used to assess the subject’s performance; and
• the standardized criteria are employed to interpret that performance.

If any one of the standardized test elements is changed, the validity of the test as a reliable or accurate gauge of blood alcohol level or state of intoxication is compromised.

Destroying the Myth of Scientific Infallibility: Attacking the Validity of the Horizontal Gaze Nystagmus Test

Every field sobriety test involves numerous potential areas for officer error in both the administration of the test and the interpretation of its results. One of the field sobriety tests, the Horizontal Gaze Nystagmus Test, is a test in which the suspect is asked to follow a light with his or her eyes as the officer moves it from side to side. The concept that underlies this test is that the presence of a central nervous system depressant, such as alcohol, in a person’s system will, at certain levels, affect that person’s pupil size, his ability to smoothly track on objects, and his ability to control the muscles that influence eye movement. Through this test, the officer is attempting to assess factors such as pupil size, tracking, smooth pursuit, and what is termed “distinct” nystagmus at “maximum deviation.” The Horizontal Gaze Nystagmus Test, like other so-called “field sobriety tests”, is vulnerable to numerous potential areas of attack by the defense.

Assessing Equal Tracking and Equal Pupil Size

In this phase of the test, the officer must complete several sets of passes. The first set of passes is designed to confirm equal tracking and equal pupil size. At the same time that the officer is looking for equal tracking, the officer is also required to look for and confirm that the pupils are of equal size. Even if the officer is doing his best to complete this test, often by the side of the road and in poor lighting conditions, the officer lacks the medical training or skill to make a correct evaluation of pupil size.

Evaluating Smooth Pursuit

In this phase, the officer is looking for a lack of smooth pursuit. If a lack of smooth pursuit is detected, a clue is scored for the eye in which the officer observed a lack of smooth pursuit. These clues are considered to be indicators of either excessive blood alcohol level or state of impairment.

The validity of any results obtained in this phase is totally dependent on the officer’s ability to administer the test perfectly and without even the smallest deviation from NHTSA guidelines. The NHTSA requires that the stimulus be moved at a speed that takes at least 2 seconds from the center position to the side position. In the field and under conditions that are not controlled, the officer must make his best estimate of speed and timing, while at the same time attempting to make an evaluation as to the suspect’s performance.

Distinguishing “Distinct” Nystagmus and “Maximum Deviation”

A third phase in the Horizontal Gaze Nystagmus test is designed to determine whether the person has what can be termed “distinct” nystagmus at some point of “maximum deviation”. Nystagmus is an involuntary jerking of the eye in response to a loss of muscle control. Maximum deviation is the point at which the eye has moved fully to one side and cannot move any further. For this phase to be properly administered, the stimulus must be moved from the center position to the person’s far left at a rate taking at least 2 seconds, held for at least 4 seconds, and then moved back to the center position at the same 2 second rate. Each pass for each eye must take at least 8 seconds and the four passes together must be at least 32 seconds. The officer must then attempt to distinguish “distinct” nystagmus and identify that point when the subject’s eye cannot move any farther to the side.

The most important issue in this phase, as in other phases, is whether the officer has correctly administered the test. If the test has not been administered in exact compliance with NHTSA requirements, then any results obtained from that test are unreliable and will not shed any light on the issues in a DUI investigation. For the test to be administered correctly, the officer must perfectly recreate the speeds required for the test to be considered valid, including moving a stimlus at a rate taking at least 2 seconds, holding if for at least 4 seconds, and then moving it back to the same position at the same 2 second rate.

Assuming that the test itself is administered perfectly, a tall order in light of the roadside conditions and other factors which generally undermine the reliability of DUI “tests” done in the field, several issues still swirl around the officer’s ability to accurately distinguish “distinct” nystagmus and to evaluate the suspect’s point of “maximum deviation.” In this phase of the test, the officer must distinguish between what might be termed regular “nystagmus” or involuntary jerking of the eye, and what can be labeled “distinct” nystagmus. The NHTSA officer training manual itself recognizes that most people will exhibit some visible “nystagmus” when the eye is held at maximum deviation. Therefore, the trick is to distinguish between what is “regular” or “normal” and what can be considered “distinct” or “unusual”. Since nystagmus will be naturally present the individual subject, it becomes a matter of evaluation and interpretation as to whether that nystagmus was in fact magnified by any type of central nervous system depressant, such as alcohol, in the person’s system. The test’s validity also relies on the officer’s ability to correctly identify the point of “maximum deviation” at the same time that he is administering the test in the field. The problem with this phase of the test is that it is open to the evaluation and judgment of each individual officer. Therefore, although the horizontal gaze nystagmus field sobriety test is presented as a scientific and objective “test”, it is deeply flawed for two reasons: (1) its administration cannot be effectively controlled or standardized when performed under conditions in the field and (2) the “results” it yields are completely subjective and susceptible to the varying perceptions and interpretations of individual officers.

Common Officer Mistakes

Any errors in the administration of the test will produce results which are not accurate or reliable indicators in a DUI investigation. For example, a common mistake called “looping” the stimulus may inadvertently cause the subject to display exactly the symptoms that the officer has been taught to look for in attempting to identify intoxication.

Common officer mistakes which call into question the reliability and accuracy of test results in include:
• moving the stimulus too quickly or too slowly on individual passes;
• holding the stimulus either closer than what is required or further away than what is required;
• not holding the stimulus for at least four seconds at that point of “maximum deviation” when looking for the presence of “distinct nystagmus”;
• and curving the stimulus upward, downward or around (also called “looping”) as it is being moved.

All of these mistakes by officers, mistakes which can easily occur when operating “under the influence” of conditions in the field, will actually produce just the results that the officer is looking for and may then falsely identify as indicators of alleged alcohol intoxication.

Any error in the administration of the field sobriety test can lead to results that are not accurate indicators as to a person’s state of intoxication. For example, if the stimulus is not moved at a constant rate, it is possible to actually induce a lack of smooth pursuit and therefore give a false clue as to a person’s level of intoxication. Therefore, varying the speed can actually induce an appearance of just what the examiner is looking for during the test. Another potential area of operator error during the Horizontal Gaze Nystagmus Test involves the length of time the officer takes to make confirming observations. As a practical matter, it takes at least two seconds and frequently longer to make the confirming observations once the stimulus has stopped. Should the officer rush through this phase or fail to accurately estimate the time period involved, the officer will simply not have the opportunity to make all the necessary observations. There may also be a potential problem raised should the officer raise the stimulus above normal horizontal eye level, in which case the test would be engaging not only the muscles in the eye controlling horizontal movement but the eye muscles involved in vertical and diagonal movement of the eye as well. This may lead to confusion of test results. Another potential problem area that would call into question the accuracy of test results has to do with the conduct of the suspect himself. Specifically, in order to have a correctly administered Horizontal Gaze Nystagmus Test, the subject must have his head held still during the entire test. If this is either not explained to the suspect or the suspect does not follow these directions, the results will not be accurate or reliable indicators of any state of alleged intoxication. Given all the potential pitfalls surrounding the Horizontal Gaze Nystagmus Test, there are many areas of attack open to the defense to undermine the validity of this test result.

Lack of Specificity and Misidentification

Assuming that the test is administered perfectly by the officer in the field and all the clues correctly perceived and interpreted exactly as the scientists who designed the test would have done, there are still questions about the test itself as an accurate and reliable investigatory tool. For example, although it is used as an alleged indicator of alcohol presence or excess, the Horizontal Gaze Nystagmus test is in fact unable to distinguish alcohol from any number of a host of other central nervous system depressants that might be present in a person’s system. In addition to its inability to pinpoint the presence of alcohol, the test results themselves may also be misleading. Outside of alcohol intoxication or excessive blood alcohol level, there are a host of medical conditions, ranging from disorders affecting the inner ear to brain issues, which might also intensify or exaggerate that nystagmus which is naturally present. Therefore, the presence of indicators or “clues” on the Horizontal Gaze Nystagmus test might mistakenly lead officers down the road toward assuming alcohol intoxication when a subject in fact has an ailment such as an inner ear infection, other medical issues affecting balance, coordination, or muscle control, or various disorders of the brain. Given the “test’s” lack of specificity and its susceptibility to producing misleading results, the reliability of the Horizontal Gaze Nystagmus test as an investigatory tool is further undermined.

Other Standardized Field Sobriety Tests: The Walk and Turn and the One Leg Stand

Like the Horizontal Gaze Nystagmus Test, the other standardized field sobriety tests are susceptible to officer error, misinterpretation, and faulty administration which can compromise the validity of the test results.

Walk and Turn Test: The idea behind the Walk and Turn Test is to require the suspect to divide attention among mental tasks and physical tasks, involving comprehension of instructions, processing information, recalled memory, and balance and coordination. Officers are taught that the Walk and Turn standardized field sobriety test is one of the most sensitive psycho-physical tests, or a test that effectively evaluates your brain’s ability to control your body. This walk and turn test must be conducted on what is termed a “reasonably smooth flat surface” with enough room for the suspect to take nine heal to toe steps. The officers are instructed that if a line is not available, it should be explained to the subject to walk on an imaginary straight line. The officer must then visually evaluate whether the suspect is walking this imaginary straight line. This test, which calls for a visual estimate of the suspect’s performance in comparison to a line that does not exist, is plagued by potential for misinterpretation. The Walk and Turn Test requires the suspect to stand in a heel-to-toe fashion with his arms at his side while a series of instructions are given. Then, the suspect must take nine heel-to-toe steps along a line, turn in a prescribed manner, and take another nine heel-to-toe steps along the line back toward the officer. All of this must be done while counting the steps aloud, keeping his arms at the sides, and looking at his or her feet. If the suspect has a level of coordination and understanding which is different from what the test anticipates, is nervous, tired, functioning under limited lighting conditions, performing the test on an uneven surface or along the roadside with the distraction of passing traffic, all these factors will cast doubt on the usefulness of the Walk and Turn Test as a valid indicator of the suspect’s alleged blood alcohol level or state of intoxication.

One Leg Stand Test: The One Leg Stand is designed to judge motor skills, balance and coordination, and the ability to perform a simple mental task such as counting at the same time that the suspect controls his body movements. Again, there are a number of other factors, rather than alleged alcohol intoxication or blood alcohol level, which may explain deficient performance on this test. These factors, including the environmental testing conditions, the officer’s ability to effectively communicate with the suspect and explain the test, and the suspect’s own characteristics, such as nervousness, illness, tiredness, or other physical limitations, can all affect the suspect’s ability to satisfactorily perform this test. Officers are taught that there are a maximum number of four validated “clues” associated with the One Leg Stand Test, including swaying, using arms to balance, hopping and putting the foot down. They are further taught that 65% of suspects who exhibit at least two out of the possible “clues” will have a blood alcohol content at or above .10%. They are taught this despite the fact that such alleged “clues”, ranging from swaying to hopping to putting your foot down, can easily be caused by many factors other than intoxication or excessive blood alcohol level.

Alternative Field Sobriety Tests: Equally As Flawed

There are other field sobriety tests which are not viewed as “standardized field sobriety tests”, but which are nevertheless approved and viewed by law enforcement as accurate indicators of a person’s alleged blood alcohol level or state of intoxication. These include the Rhomberg Balance Test, the Finger to Nose Touch Test, the Hand Pat Test, the Finger Count Test, and the Verbal or Written Alphabet Test.

Where an officer suspects that a driver may be under the influence of drugs and not just alcohol, the officer may choose to give the Rhomberg Balance Test, in addition to a battery of alleged “drug recognition evaluation” tests. The assumption of the Rhomberg test is that drugs operate to speed up the suspect’s internal body clock so that the suspect, rather than estimating 30 seconds as 30 seconds, may open his or her eyes after only 10 or 15 seconds and believe that 30 seconds have passed. Other drugs may slow down the body’s internal clock so that the suspect keeps his or her eyes closed for 60 seconds or more. In evaluating the suspect’s performance on the Rhomberg Balance Test, officers are looking for six major clues: the suspect’s ability to follow instructions, the amount and direction in which the suspect sways, the suspect’s estimated passage of 30 seconds, the presence of eye lid tremors and/or body tremors, the suspect’s muscle tone, and any statements or unusual sounds made by the suspect when performing the test. As with the other more standardized field sobriety tests, there are many other factors which come into play and could explain a suspect’s deficient performance on this test, rather than the suspect’s alleged state of intoxication or excessive blood alcohol level.

As you can see, although field sobriety tests are relied on by law enforcement as allegedly scientific and reliable indicators of a person’s blood alcohol level or state of intoxication, they are in fact open to many errors both in administration and interpretation. As acknowledged by law enforcement, these tests only have validity if they are performed perfectly by the officer administering them. Furthermore, even if they are performed (as in the case of horizontal gaze nystagmus test) or explained (as in the case of the walk and turn or one leg stand case) perfectly, they are still susceptible to errors in interpretation by the arresting officer. Further, a suspect’s performance on these so called tests may be deemed deficient as a result of factors other than alcohol intoxication or blood alcohol level. These factors may include environment factors, physical factors, and the officer’s ability to both accurately perceive the suspect’s performance and analyze the performance, often at the same time as he is administering the test itself.

Your Field Sobriety Test Results

At the Law Office of Jennifer Zide, we recognize that what are presented as “facts” in police reports, from vague officer observations to the results of so-called “field sobriety tests”, are in fact open to interpretation and officer error. The role of your defense attorney is to analyze and challenge all the information against you, to dismantle the assumptions of the police report, and to bring to light the weaknesses at the heart of the prosecution’s case. At the Law Office of Jennifer Zide, we are here to protect your individual rights. Contact us today to discuss the details of your case in your free initial consultation.