What is the first clue observed during the Horizontal Gaze Nystagmus (HGN) test?

The first clue observed during the Horizontal Gaze Nystagmus (HGN) test is a lack of smooth pursuit. This indicates that the eye is unable to smoothly follow a moving object, which is a key indicator that may suggest impairment. When a subject’s eye exhibits a jerky movement rather than a smooth tracking motion as it follows an object, it signifies that the person may be under the influence of alcohol or other substances.

Identifying this lack of smooth pursuit is critical for law enforcement officers conducting the HGN test, as it serves as the initial sign of potential impairment before further observations are made, such as nystagmus at maximum deviation or involuntary eye movements that occur during other phases of the test. Recognizing this early sign allows officers to assess the driver's condition effectively and make informed decisions regarding their sobriety.