Examining the HGN Test in DWI and DUI Cases: A Defense Perspective

By Sullivan Rice

When discussing field sobriety tests, it’s essential to recognize an ongoing debate about the terminology used—should we even call them "tests"? Unlike traditional tests, these assessments are not inherently pass or fail. They are better characterized as divided attention tasks designed to elicit specific clues regarding a driver's potential impairment. While this article will refer to them as field sobriety tests for consistency, it's important to understand their limitations.

A pivotal component of these tests is the Horizontal Gaze Nystagmus (HGN) test. This test is one of the three standardized assessments used by law enforcement to gauge impairment. During the HGN test, an officer asks the driver to follow a slowly moving object, such as a pen or flashlight, while observing their eye movements for signs of nystagmus. This article delves into the intricacies of the HGN test, particularly how an experienced defense attorney can challenge its validity in court. Much of the information presented here draws from the Minnesota training manual for field sobriety tests, which is continuously updated to reflect current scientific understanding and best practices.

What is Horizontal Gaze Nystagmus?

Nystagmus refers to the involuntary jerking of the eyes, which can occur naturally or be exacerbated by alcohol or other substances. Importantly, individuals experiencing nystagmus are typically unaware of it and cannot control it. However, various types of nystagmus exist, and distinguishing between them is crucial since officers may misinterpret them.

1. Vestibular Nystagmus occurs due to inner ear disturbances and can be triggered by rapid movements, like spinning. If a driver has recently engaged in such movements, this type of nystagmus could explain any observed signs during the HGN test.

2. Neural Nystagmus includes Optokinetic and Physiological Nystagmus, neither of which is related to substance use. For instance, watching moving strobe lights can induce Optokinetic Nystagmus, while Physiological Nystagmus is a common, natural occurrence in most individuals.

3. Pathological Nystagmus arises from medical conditions such as brain disorders. Officers are trained to check for equal pupil size and other indicators before administering the HGN test. If these protocols are ignored, the validity of the test results can be called into question.

Administering the HGN Test

The HGN test comprises three key exercises, each meant to identify specific signs of impairment. However, the accuracy of these observations is heavily dependent on the officer's adherence to established protocols, which is often not the case.

- Lack of Smooth Pursuit: This exercise assesses whether the subject's eyes can smoothly follow a moving object. If the officer rushes this process, it may compromise the test's reliability.

- Distinct Nystagmus at Maximum Deviation: Officers must hold the stimulus at the maximum deviation point for at least four seconds to accurately observe any pronounced jerking. Rushed administrations can lead to erroneous conclusions about impairment.

- Onset of Nystagmus Prior to 45 Degrees: This exercise examines if nystagmus occurs before the eye reaches a 45-degree angle from the center. As with the other tests, the speed of stimulus movement must adhere to specific guidelines to ensure validity.

Officers can potentially observe six clues during the HGN test, but it’s critical to note that even with proper administration, the test is only 88% accurate. When deviations occur, the reliability of the test diminishes significantly.

Defense Strategies Against HGN Test Results

Defendants have multiple avenues to challenge HGN results in Minnesota. While it may be challenging to exclude the test entirely from trial, the focus can shift to questioning its weight and validity.

1. Officer Training and Certification: Examining whether the officer followed proper protocols is essential. Any deviation can raise doubts about the test's reliability.

2. Medical Conditions: Presenting evidence of medical issues that might cause nystagmus, such as inner ear disorders or neurological conditions, can effectively challenge the test results.

3. Environmental Factors: Arguing that external conditions—like poor lighting or distractions—affected the test can also provide a basis for creating reasonable doubt.

Conclusion

Understanding the complexities of the HGN test is vital for both defendants and legal professionals. While the test is often viewed as a cornerstone of field sobriety assessments, it is not infallible. Defendants should be aware of their rights during DUI investigations and consider seeking experienced legal representation to navigate these challenges.

In times of legal uncertainty, trust Jack Rice Defense to provide the expertise and support you need. Contact Jack Rice today to ensure your case is handled with the utmost care and professionalism.