Why is it important for the officer to keep the stimulus at eye level during the HGN test?

Maintaining the stimulus at eye level during the Horizontal Gaze Nystagmus (HGN) test is crucial because it ensures accurate observation of the subject's eye movements. When the stimulus is positioned at eye level, the officer can effectively monitor how the eyes react to the movement of the object. This position allows the officer to observe for key indicators of impairment, such as the presence of nystagmus, which is characterized by involuntary eye movement.

Proper positioning at eye level helps to minimize any potential distortions in the subject's gaze that could arise from variations in angle. This is essential for reliable measurements, as any deviation might alter the responses of the eyes, leading to misleading interpretations. Therefore, keeping the stimulus at eye level enhances the overall validity of the test results, allowing the officer to make more accurate assessments regarding impairment related to alcohol or drug use.