When forming an argument concerning field sobriety exams, a good defense lawyer should have the advantage. Regardless of how a defendant performs on the evaluations, there is always a persuasive argument. Because the State presumes field sobriety exams have a level of accuracy, if a defendant performs well, then an attorney can argue that the defendant wasn’t impaired. On the other hand, ff the defendant performs poorly, then an attorney argue can argue that the tests are unreliable and don’t truly show that someone is impaired. As a practical point, though, when using either argument you want to avoid siding with the prosecution, which is what a Wisconsin defendant recently did in his DUI trial.
When pulled over for suspicion of DUI, the Wisconsin defendant performed poorly on the Horizontal Gaze Nystagmus field sobriety test (eye test). The test checks for jerking eye movements, nystagmus, allegedly caused by alcohol consumption. The defendant argued that the HGN test was inaccurate, because nystagmus can be caused by conditions other than alcohol. He’s right. For one, everyone has natural nystagmus. Also, nystagmus can be caused by flashing lights, variations in heat and cold, or wind – many of the normal conditions of a roadside traffic stop. In a controlled environment, though, like a courtroom, the HGN test will be more accurate. To prove his point, in exchange for provided testimony the defendant consented to an HGN test. He aced the test in the courthouse, discredited his credible argument, and was convicted of DUI.