07/03/2024
The DUI defense attorney should challenge the Horizontal Gaze Nystagmus (HGN) test in every DUI if this field sobriety test was performed. The photo here shows an officer performing the test by moving a pen horizontally in front of the suspect's eyes.
The HGN test is a key component of field sobriety testing protocols used by law enforcement officers to detect impairment from alcohol or drugs. This test, developed and standardized by the National Highway Traffic Safety Administration (NHTSA), serves as a non-invasive, quick, and relatively reliable method for assessing a person's level of intoxication. The HGN test hinges on the observation of involuntary eye movements known as nystagmus, which can be exaggerated by the consumption of alcohol or certain drugs. This essay delves into the scientific basis, administration, effectiveness, and legal implications of the HGN test.
SCIENTIFIC BASIS FOR THE HGN TEST
Nystagmus refers to the involuntary jerking of the eyes, which can occur naturally in response to various stimuli. Horizontal gaze nystagmus is specifically observed when the eyes move horizontally. In a sober individual, these movements are generally smooth and controlled. However, alcohol and certain drugs can impair the central nervous system, affecting the brain's ability to control eye muscles. This impairment can result in more pronounced nystagmus, which becomes noticeable when the individual attempts to follow a moving object with their eyes.
The underlying reason for this phenomenon is that alcohol and certain drugs can affect the function of the vestibular system and the cerebellum, both of which play crucial roles in eye movement control. When impaired, the brain's ability to coordinate these movements diminishes, leading to the characteristic jerking motion observed in nystagmus. The HGN test capitalizes on this physiological response, providing a relatively objective measure of impairment.
ADMINISTRATION OF THE HGN TEST
The administration of the HGN test involves a series of standardized steps to ensure consistency and reliability. First, the officer instructs the suspect to stand still with their feet together and hands at their sides. The officer then positions a stimulus, such as a pen or flashlight, approximately 12-15 inches from the suspect's face, slightly above eye level. The suspect is asked to follow the stimulus with their eyes only, without moving their head.
The officer observes the suspect's eyes for three specific indicators of impairment in each eye:
(1) The inability to smoothly pursue the object (smooth pursuit).
(2) Distinct and sustained nystagmus when the eye is held at maximum deviation (distinct nystagmus at maximum deviation).
(3) The onset of nystagmus before the eye reaches a 45-degree angle (onset of nystagmus prior to 45 degrees).
Each of these indicators is scored, and the presence of four or more out of six possible clues is generally considered indicative of impairment.
EFFECTIVENESS & RELIABILITY
The HGN test is widely regarded as one of the most reliable field sobriety tests. Studies conducted by the NHTSA have demonstrated that the HGN test has a high correlation with blood alcohol concentration (BAC) levels. For instance, the test is estimated to be about 77% accurate in detecting BAC levels of 0.10% or higher. This makes it a valuable tool for law enforcement officers in the field, providing a quick and non-invasive assessment of impairment.
However, the effectiveness of the HGN test can be influenced by various factors. Proper training and adherence to standardized administration protocols are crucial for accurate results. Environmental conditions, such as poor lighting or distractions, can also affect the test's reliability. Moreover, certain medical conditions and medications can cause nystagmus, potentially leading to false positives. As such, the HGN test is typically used in conjunction with other field sobriety tests and evidentiary breath or blood tests to corroborate findings.
LEGAL IMPLICATIONS
The HGN test holds significant weight in legal proceedings related to DUI charges. Courts have generally accepted the test as scientifically valid when administered correctly by a trained officer. The results of the HGN test, combined with other evidence such as breathalyzer or blood test results, can form a strong basis for establishing impairment.
However, the admissibility of the HGN test in court can be challenged on various grounds. Defense attorneys may question the officer's training, the conditions under which the test was administered, or the presence of medical conditions that could have affected the results. Ensuring the integrity of the HGN test through rigorous training and adherence to standardized procedures is therefore critical for its effectiveness in legal contexts.
CONCLUSION
The Horizontal Gaze Nystagmus test is a scientifically grounded, reliable tool for detecting impairment due to alcohol or drugs. Its physiological basis, standardized administration, and demonstrated effectiveness make it a cornerstone of field sobriety testing. While it is not without limitations, the HGN test, when properly conducted, provides valuable evidence in DUI investigations and prosecutions. As with any scientific test, ongoing research, training, and refinement of protocols are essential to maintain its reliability and uphold its role in promoting public safety. The defendant's DUI defense attorney should challenge the Horizontal Gaze Nystagmus (HGN) test in every DUI if this field sobriety test was performed.