Legal Definitions - HGN TEST

The HGN Test, which stands for Horizontal-Gaze Nystagmus Test, is a standardized field sobriety test used by law enforcement officers to detect signs of impairment, most commonly due to alcohol or certain drugs.

During the test, an officer observes a person's eyes as they follow a moving object (like a pen or a finger) horizontally. The officer is looking for involuntary jerking of the eyeballs, known as nystagmus, which can become more pronounced or apparent when a person is under the influence. The presence and characteristics of this involuntary eye movement can provide clues to an officer about a person's level of impairment.

• Example 1: A driver is pulled over late at night for repeatedly drifting out of their lane. The police officer, suspecting the driver might be impaired, asks them to perform a series of field sobriety tests. As part of this, the officer administers the HGN test by holding a pen approximately 12-15 inches from the driver's face and moving it slowly from side to side. The officer observes that the driver's eyes exhibit distinct, involuntary jerking movements before reaching the maximum deviation, which is noted as a sign of potential alcohol intoxication.

  Explanation: This scenario illustrates the HGN test being used as a primary tool during a traffic stop to assess a driver's sobriety based on their physiological response, specifically the involuntary movement of their eyes.

• Example 2: Following a minor collision, one of the drivers involved appears confused and has difficulty answering questions clearly. When a police officer arrives to investigate, they decide to administer field sobriety tests to determine if impairment contributed to the accident. During the HGN test, the officer notices that the driver's eyes do not track smoothly and show significant nystagmus, or jerking, even at slight angles of gaze. This observation, combined with other indicators, strengthens the officer's belief that the driver is under the influence of a substance.

  Explanation: Here, the HGN test serves as a crucial piece of evidence in an accident investigation, helping the officer establish probable cause for an arrest by identifying physical signs of impairment in one of the drivers.