Which field sobriety test assesses the involuntary jerking of the eyes while moving to the side?

The Horizontal Gaze Nystagmus (HGN) test is designed to evaluate the involuntary jerking of the eyes as they move horizontally from side to side. During this test, a law enforcement officer will ask the subject to follow a pen or another object with their eyes while keeping their head still. As the eyes follow the object, any jerking that occurs may indicate impairment. Typically, greater levels of impairment, such as from alcohol consumption, can lead to more pronounced eye jerking, which the officer observes to assess the subject's sobriety.

In contrast, the Vertical Gaze Nystagmus test focuses on the eye movement in a vertical direction rather than horizontal. The Balance Test and the Roadside Assessment involve different physical tasks and skills that do not specifically target eye movement or nystagmus assessment. Thus, the correct answer specifically related to assessing the involuntary jerking of the eyes while moving to the side is indeed Horizontal Gaze Nystagmus.