What does HGN stand for in relation to field sobriety testing?

HGN stands for Horizontal Gaze Nystagmus, which is a key component of the Standardized Field Sobriety Tests (SFST). This test involves observing the eyes of a suspect as they follow a moving object, typically a pen or a finger, in a horizontal plane.

The presence of nystagmus, which is an involuntary jerking of the eyes, can be indicative of impairment, particularly from alcohol. When performing the HGN test, officers look for specific characteristics of the eye movements, such as how smoothly the eyes track the object and whether the jerking occurs before reaching the maximum deviation.

This test is based on scientific principles that link the function of the vestibular system in the inner ear, which can be affected by alcohol, to the eye movements being measured. Understanding HGN and its implications is essential for officers when assessing a suspect's level of intoxication.