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Horizontal Gaze Nystagmus (HGN) Field Sobriety Test


By: Cory Yager, Ex-Cop and Criminal Defense Attorney in Atlanta

The HGN Test or Horizontal Gaze Nystagmus Field Sobriety Test for DUI-Alcohol Cases

Horizontal Gaze Nystagmus EyeballThe horizontal gaze nystagmus test or evaluation (commonly known as the HGN or HGN test) is one of the three NHTSA standardized field sobriety tests (SFST) that police offer to motorists (who are suspected of DUI-alcohol while operating a vehicle). Typically, the law enforcement officer making the traffic stop is the one who administers the eye test to the DUI suspect at the roadside, as part of a driving under the influence DUI-DWI investigation.

Once a driver is in contact with a police officer, after being detained for an alleged traffic ticket or at a DWI-DUI checkpoint, that suspected drunk driver will be asked to submit to roadside tests. EVERY police-requested field sobriety test is VOLUNTARY, and DUI specialists will tell you to NEVER take any of these optional tests. Even if you have submitted to these roadside tests, our criminal lawyers near me know how to neutralize the bogus testing at pre-trial motions or at trial, if needed.

What Is the HGN Test?

The HGN is a tracking test of the eye movements of the suspected intoxicated driver but is not a vision test. Law enforcement officers are told this exam is the “most reliable” field sobriety test, and it is supposed to be the first test given. Since the field sobriety tests promulgated by the National Highway Traffic Safety Administration (NHTSA) will be one of the key items of evidence in an impaired driving (driving under the influence of alcohol) case, the task of DUI lawyers who are defending a criminal case is to eliminate or neutralize the roadside HGN evaluation.

Clues of Horizontal Gaze Nystagmus

How Many NHTSA Standardized Field Sobriety Tests Are There?

Horizontal Gaze Nystagmus TestOne of three (3) standardized field sobriety tests sanctioned by NHTSA, the nystagmus test is a psychophysical exam that deals with involuntary jerking of the eye (which doctors call saccadic movement) as the test subject’s eyes move together, side to side. The person being tested for HGN keeps his or her head still and tries “to use their eyes only” to follow the object (which police call “the stimulus”) as it is being passed from side to side, by the police officer. The officer then can see how your eyes “track” the moving object passing across your field of vision. Multiple “passes” are required, as the officer seeks to observe any “clues” or “cues” obtained by the police officer’s separate observation of each eye.

Pre-Screening is Required Before the HGN Tests Are Considered to Be Valid

To properly score and perform horizontal gaze nystagmus on any person, the NHTSA-trained police officer is mandated to medically qualify the test subject. This medical qualification screening procedure, to find out if the person is a suitable “subject,” is accomplished by asking the citizen questions about eye problems and medications being taken, as well as checking the detained person’s eyes for resting nystagmus (congenital nystagmus, that always exists in some test subjects, especially those with a prior concussion). Plus, before attempting any of the three standardized HGN tests, the investigating police officers must use a separate, preliminary, equal tracking screening test during which a stimulus is moved briskly across the test subject’s field of vision, to eliminate the possibility of head trauma or brain lesions.

How Is the HGN Eye Nystagmus Test Performed?

Horizontal Gaze Nystagmus Test Error

Horizontal Gaze Nystagmus Test Error

For all the “horizontal gaze” tests, the position of the stimulus must be held slightly above eye level, or approximately at the bottom of the person’s eyebrows. Holding the stimulus too high can TRIGGER gaze nystagmus, even when little or no alcohol is present in the person’s system. This “false positive” problem was proven in NHTSA’s so-called “Robustness Study,” conducted in 2007.

The three types of HGN eye test passes (made by investigating police officers) are called lack of smooth pursuitdistinct and sustained nystagmus at maximum deviation, and the onset of nystagmus as the stimulus is slowly moved out to 45 degrees from the center of the person’s face. Since each eye is separately “scored” and three different types of horizontal nystagmus are being checked, a maximum of six clues (or cues) can be obtained, for the field sobriety test scoring sheet.

How Many HGN Clues Indicate That a Person Is “Over the Legal Limit?”

All police officers who attend the NHTSA-based field sobriety test training are taught by their instructor that the horizontal gaze test is the most valuable and reliable of the three standardized field tests sanctioned by the National Highway Traffic Safety Administration. They are told that it accurately predicts who should be arrested for driving while intoxicated, based on four or more clues or cues being observed, and that these clues mean that the person is likely at 0.08 grams percent or higher.

So, being scored at either four clues or six clues is an “arrest decision,” according to NHTSA SFST training. Police falsely testify that “observing four or more clues on HGN indicates IMPAIRMENT,” and this claim is a lie. Dr. Marcelline Burns, the person who CREATED the NHTSA field tests, verified this fact at a legal seminar held in California.

Vertical Gaze Nystagmus After the HGN Testing Is Finished

Horizontal Gaze Nystagmus Eye TestThe horizontal nystagmus gaze test has a maximum of six clues and is followed by the vertical gaze nystagmus test, where the officer moves the stimulus up and down, which has NO clues. These vertical passes are administered to see if vertical gaze nystagmus (VGN) is present, in your eyes. The VGN eye test is not a scored test, by counting any “clues,” and only identifies a possible high dose of alcohol for that individual. But, this claimed statistical correlation of a VGN test has not been scientifically proven to do what police are trained to testify that it WILL do, and such testimony should be excluded by way of your DUI defense attorney filing and arguing a pre-trial motion in limine, in your DUI case.

After the Nystagmus Tests, What Other Field Sobriety Tests Are Given?

Police are trained to try to obtain all three of the standardized field sobriety test exercises. Two other roadside evaluations are typically requested by police officers, which are the “walk-and-turn” (WAT) evaluation and the “one-leg-stand” (OLS) evaluation. Neither of these is a psychophysical test (which HGN would be classified) but are called “divided attention” tests.

The Walk and Turn Divided Attention Test

DUI Walk and Turn TestIn simple terms, the subject attempting the walk-and-turn is being scored for following specific NHTSA-mandated instructions when walking, while touching heel-to-toe along a line for nine steps out, with arms against your sides, and nine steps back, after making a specific type of counterclockwise turn. Up to eight clues can be observed, and if two of the eight clues are noticed, the person is then claimed to be over the legal alcohol limit.

The One Leg Stand Divided Attention Field Test Is the Most Difficult and Unfair

The last field sobriety test given is the 30-second “stand on one leg” one-leg-stand test. Like the walk-and-turn and the HGN tests, detailed and precise instructions from the police officer are required for the exercise to be considered “valid.” This non-scientific field test evaluation is a timed test lasting 30 seconds which can produce up to four clues, and if two of the four are observed by the arresting officer, he or she will claim that you “failed” and that this means that you are likely to be over the alcohol legal limit.

Over half of all people age 40 or above cannot perform this evaluation when totally sober. Plus, individuals who are noticeably overweight are in the same predicament. Tellingly, the NHTSA “manual” does not exclude either category of test subjects from being evaluated and arrested, based on their predictably bad performance. These types of omissions are why true scientists who have a medical background say that the unfair field sobriety tests are designed to fail.

Hiring an Expert in Beating Field Sobriety Tests as Your DUI Attorney

How many DUI lawyers are former police officers who made DUI arrests? One of our DUI law firm partners, Cory Yager, made over 1000 DUI arrests as a law enforcement officer over his police career, spanning nearly ten years. He is both a practitioner and an Instructor in the SFSTs.

After his years of employment as a police officer, DUI defense attorney Cory Yager became a DUI lawyer, defending people in drunk driving defense cases. Plus, both DUI Specialist Larry Kohn and drunk driving book author William C. “Bubba” Head, have been SFST Instructors in the NHTSA three-test battery of roadside tests since 1999. What other DUI law firm in GA can match those credentials?

For a FREE lawyer consultation near me (within a 50-mile radius of Atlanta) contact our DUI attorneys, and a Partner will assess your DUI case. Because the Georgia DUI court for your case may be five hours away in south Georgia, our firm can refer you to a highly-trained DUI lawyer near me (in your location).

Any attorneys we recommend in Georgia or other states will be fully informed about how our award-winning attorneys would approach winning your drunken driving case. Call 404-567-5515  for FREE legal advice from our THREE Field Sobriety Instructor DUI defense lawyers.


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