The Horizontal Gaze Nystagmus (HGN) test is one of three standardized field sobriety tests (SFSTs) validated by the National Highway Traffic Safety Administration (NHTSA). It is also a test that police frequently administer during traffic stops when intoxicated driving is suspected. Though the NHTSA recognizes the HGN as a test that can indicate impairment, this test is not fool-proof. It has disadvantages, making admitting it as evidence problematic.
What is a Horizontal Gaze Nystagmus Test?
The Horizontal Gaze Nystagmus test is one of three standardized field sobriety tests used by the police in Alabama to help determine whether a driver is under the unlawful influence of alcohol or drugs.
How is the HGN Test Performed?
The officer conducting the HGN test should provide clear verbal instructions to the driver. The police officer should tell the driver to stand still, place hands to the side, and keep their heads still. Then, they must be properly instructed to look at a stimulus, like a pen or another object, and follow it with both eyes while the officer moves the stimulus from right to left.
The officer assesses the driver's eyes while moving the object from side to side. HGN tests, however, are very technical in their application. Proper administration involves specific requirements on the distance between the stimulus and the driver's nose (12 - 15 inches), the timing and length of holds (hold the stimulus for at least 4 seconds at the maximum deviation), and the number of times and ways the stimulus is passed back and forth.
The HGN test is meant to measure the involuntary jerking of the eye, known as nystagmus. A driver with a high blood alcohol concentration may exhibit this jerking as the driver gazes toward the side while following the stimulus.
Three Major Clues of Intoxication
Police look for three significant clues while administering the HGN test. Each eye is assessed for these three clues, so there are actually six possible indicators of intoxication. If the officer determines four clues exist, that is supposed to indicate the driver's blood alcohol content (BAC) level is above 0.08 percent.
- Clue 1 involves the onset of nystagmus in either eye before 45 degrees.
- Clue 2 involves nystagmus in either eye when the eye gazes as far as possible to the right or left – in this case, there is a sustained and distinct jerking.
- Clue 3 occurs when the driver cannot follow the stimulus – known as a lack of smooth pursuit.
Each clue requires specific motions or manners in which the stimulus is held or passed. Each clue also requires different timing. For example, the movement of the stimulus to determine the lack of smooth pursuit should be two seconds out and back to each eye while it is four seconds to move the stimulus from eye to the driver's shoulder to determine the onset of nystagmus prior to 45 degrees.
Ways to Challenge the HGN Test in Alabama
HGN tests can be effectively challenged by arguing against their reliability (these tests are highly subjective) or proving improper administration (these tests require following strict and specific technical rules). Also, these tests can be challenged based on matters not associated with the test itself but related to the driver or to the environment.
Common Challenges to the HGN Test
- Unreliable based on police officer's subjective estimations and preconceived notions.
- Unreliable based on the police officer's failure to administer the test properly
- Unreliable based on external factors
Common External Causes of Failed HGN Tests
- Bad weather
- Administered at night in darkness or during the day with a glaring sun
- Bad roads or other environmental issues
- Patrol car lights flashing or other lighting issues
- Driver's pre-existing health issues or medications, like ear disorders, eye disorders, head injury or brain damage, excessive amounts of caffeine, antihistamines, barbiturates, illness like the flu or vertigo
Keep in mind that there are more than 38 non-alcohol-related causes for nystagmus, and each of these can lead to a failed HGN test.
Concerns as to reliability
The Horizontal Gaze Nystagmus (HGN) test is a commonly used field sobriety test in DUI cases, yet its reliability is far from ironclad. One of the primary concerns is the inherent subjectivity involved. Officers must visually assess involuntary eye movements as a suspect follows a moving stimulus. This evaluation can vary widely depending on the officer's training, experience, and even personal bias. Minor differences in interpretation can lead to significant discrepancies in results, making the test less objective than many assume.
Medical conditions also complicate the use of the HGN test. Some individuals naturally exhibit nystagmus, or have neurological or ocular conditions that mimic the signs of impairment, regardless of their blood alcohol content. Fatigue, stress, or the influence of prescription medications can further trigger involuntary eye movements. This means that a person might display the physical signs of intoxication even when sober, leading to a potentially erroneous conclusion.
Environmental factors play their part as well. The test is often administered in less-than-ideal conditions, such as poor lighting or distracting roadside settings. These factors can hinder accurate observation and contribute to misinterpretation. Additionally, scientific studies have shown that the correlation between nystagmus and actual impairment isn't consistent across all individuals. Variability in physiological responses means that even a well-conducted HGN test might not reliably predict intoxication levels.
Finally, the administration of the test itself is critical. Any deviation from standardized procedures can compromise its reliability. In light of these issues, while the HGN test can serve as a useful tool in building a DUI case, its limitations suggest that it should not be the sole piece of evidence used to determine impairment.
The HGN test is faulty. Your DUI defense attorney may be able to highlight these weaknesses and create reasonable doubt in the prosecution's case against you. Our DUI defense lawyer will investigate and review the results of your HGN test and challenge it accordingly.
Field sobriety tests are a way police officers gather probable cause to arrest you for DUI charges. However, these tests are rarely conducted in accordance with regulations and are faulty, given their subjective nature.
