The Horizontal Gaze Nystagmus (HGN) test is a standardized field sobriety test (FST) used by law enforcement officers to assess the potential impairment of a driver suspected of driving under the influence (DUI) of alcohol or drugs. This test focuses on involuntary jerking of the eyes (nystagmus) as the eyes track a moving stimulus, in this case, a light source. While the procedure is generally straightforward, questions often arise regarding the use of the light itself, particularly the brightness and its potential impact on the test's accuracy.
How is the Light Used in the HGN Test?
The HGN test utilizes a small, penlight-like device. The officer holds the light approximately 12-15 inches from the suspect's face and instructs the individual to follow the light with their eyes only, keeping their head still. The officer slowly moves the light horizontally, observing the subject's eyes for signs of nystagmus. The light's intensity is typically not excessively bright, aiming for a level that allows for clear observation without causing discomfort or distraction. The crucial aspect isn't the brightness per se, but the consistent, smooth movement of the light to elicit the eye movements needed for assessment.
What if the light is too bright?
A light that is excessively bright could indeed impact the accuracy of the HGN test. Extreme brightness might cause discomfort, eye strain, or even temporary visual impairment, thus interfering with the subject's ability to follow the light smoothly. This could lead to inaccurate results, potentially masking or exaggerating the presence of nystagmus. While trained officers typically understand appropriate light intensity, complaints about overly bright lights could be grounds for questioning the test's validity.
Can flashing the light affect the HGN test results?
Flashing the light during the HGN test is generally not part of the standardized procedure. The standard protocol involves a slow, consistent movement of the light. Flashing the light could introduce an entirely different stimulus, affecting the test's reliability. This erratic movement would make it impossible to accurately observe the subtle involuntary jerking characteristic of nystagmus. A rapidly flashing light could also trigger additional physiological responses not related to alcohol or drug impairment. Therefore, flashing the light is not only inappropriate but also invalidates the test.
What are the other factors that can affect the HGN test?
Several factors beyond the light's intensity can impact the accuracy of the HGN test. These include:
- Underlying medical conditions: Certain neurological or eye conditions can cause nystagmus independently of intoxication.
- Fatigue and lack of sleep: Eye fatigue can mimic some aspects of alcohol-induced nystagmus.
- Medications: Certain prescription or over-the-counter medications can affect eye movements.
- Officer training and experience: Proper training and experience are crucial for accurate observation and interpretation of the test results.
Is the HGN test admissible in court?
The admissibility of HGN test results in court varies depending on jurisdiction and specific circumstances. While it’s a commonly used test, challenges to its admissibility often focus on the officer’s training, the proper administration of the test, and the potential for error or influence from external factors. Courts typically consider all factors affecting the test's validity when making a determination.
Conclusion:
The HGN test, while a valuable tool in DUI investigations, is not foolproof. Understanding the proper procedure, the potential for error due to factors like overly bright or flashing lights, and the importance of proper officer training are critical to ensuring fair and accurate assessment. Any concerns about the administration of the test should be addressed legally and through the appropriate channels.
