What type of movement is indicative of nystagmus during the HGN test?

During the Horizontal Gaze Nystagmus (HGN) test, the type of movement that is indicative of nystagmus is sudden jerking movements of the eyes. This phenomenon occurs when the eyes are moved to the side and is characterized by involuntary, rhythmic oscillation.

Nystagmus essentially describes the way the eyes respond to movement; they may jerk in one direction and then move back smoothly, with the jerking often being more pronounced as the gaze is moved further to the side. This is particularly relevant in assessing potential impairment due to alcohol or drugs, as nystagmus can indicate a disruption in the vestibular system which affects eye coordination.

The other options detail different movements that do not accurately characterize nystagmus. Slow, deliberate eye movements are typically controlled and do not indicate impairment. Rapid blinking doesn’t reflect the jerking nature of nystagmus, and uncontrolled rolling of the eyes suggests a different type of eye movement that doesn’t conform to the defined characteristics of nystagmus observed during the HGN test.