How is the Horizontal Gaze Nystagmus test conducted?

The Horizontal Gaze Nystagmus (HGN) test is a standardized field sobriety test that specifically assesses a person's ability to follow a moving stimulus with their eyes. This test involves the officer holding a stimulus, such as a pen or a finger, in front of the subject and asking them to follow it with their eyes without moving their head. The officer observes the eyes for signs of nystagmus, which can indicate impairment due to alcohol or other drugs.

Nystagmus is an involuntary jerking of the eyes, and the HGN test is based on the premise that impairment often leads to a more pronounced and earlier onset of nystagmus as the eyes track the stimulus. This method allows law enforcement officers to gather evidence of potential impairment based on observable physiological responses.

Other options like walking in a straight line, counting while standing on one leg, or reciting the alphabet involve different motor and cognitive skills and are associated with other types of field sobriety tests, but they do not assess the specific eye movements that the HGN test evaluates.