During the HGN test, jerking movements of the eyes typically indicate what?

During the Horizontal Gaze Nystagmus (HGN) test, the observation of jerking movements of the eyes, also known as nystagmus, is a key indicator of potential impairment. Specifically, jerking is often associated with the influence of alcohol or certain drugs, which can disrupt the normal functioning of the vestibular system and the brain's coordination of eye movement. In individuals who are impaired by alcohol, the onset of nystagmus may occur at lower angles of gaze compared to those who are sober.

This response to alcohol is a critical aspect of the HGN test, as trained officers look for specific characteristics of eye movement to judge impairment levels. In contrast, normal functioning would exhibit smooth eye movements without such jerking, and medical impairments or fatigue may cause similar symptoms, but they are not specifically indicative of alcohol influence within the context of standardized field sobriety tests. Thus, the identification of jerking movements during the HGN is directly linked to assessing alcohol impairment.