What is the primary focus when conducting the HGN test?

The primary focus when conducting the Horizontal Gaze Nystagmus (HGN) test is on eye movement and tracking of the stimulus. During this test, an officer looks for specific involuntary eye movements known as nystagmus, which can indicate impairment due to alcohol or other drugs. The test involves the subject following a stimulus, typically a pen or a finger, with their eyes while the officer observes how well the eyes can smoothly track the movement.

This method is based on the understanding that alcohol impairs the central nervous system, affecting eye muscle control and leading to distinct patterns of eye movement. Key indicators the officer looks for include the onset of nystagmus at specific angles while tracking, as well as the angle of maximum nystagmus. All these observations are critical to providing a reliable assessment of potential impairment, making this focus essential in the context of DUI investigations.