Almost all DUI investigations include having a California DUI suspect perform various balance and coordination tests. These tests are referred to as field sobriety tests or FST's. The theory behind these tests is that they test a person's ability to divide attention. Driving is portrayed as a divided attention task. One has to both operate the automobile and also pay attention to other cars, pedestrians, and traffic controls on the road. There are several FST's. The most common are the horizontal gaze nystagmus, walk and turn, one leg stand, Rhomberg balance, finger to nose, alphabet, and number count. Only three of these tests, the horizontal gaze nystagmus, walk and turn, and one leg stand are recognized by the National Highway Traffic and Safety Administration (NHSTA) as having a statistical validity. These three tests are called Standardized Field Sobriety Tests (SFST's) The horizontal gaze nystagmus test consists of the arresting officer asking the DUI suspect to keep their head still and follow a stimulus such as a pen or finger while the officer moves it in front of their face. The officer is looking to see if the eyeballs jerk involuntarily (nystagmus). This is the SFST that has the greatest aura of scientific validity. However, in reality, it is junk science. There are some people who have nystagmus that is natural or caused by a medical condition. The arresting officer can cause nystagmus by moving the stimulus too fast, holding it out too long, or holding it too close to the suspect's face. Also, jerking motions by the arresting officer can cause nystagmus. As a result, this test is rarely performed correctly and properly by arresting officers. The walk and turn is a deceptively simple test, but in reality it is complex to administer. Giving the proper instructions and demonstrating the test take practice and experience. Failure to start the person off on the correct foot can sabotage the entire test and set the person up for failure. Minor sins like raising arms more than six inches for balance are counted against the test subject. There are many places to make mistakes. Sober people make many mistakes on this test given the complexity of the instructions. The one leg stand is the easiest test to administer, but for some suspects, the hardest to perform. Being asked to place your hands at your sides and balance on one foot while keeping the opposite leg perfectly strait and look down at your feet can be hard to do by the side of the road under the stress of a law enforcement detention at 3:00 in the morning. I had one trial where I asked the officer to demonstrate this test. The officer struggled, shaking and hopping before the jury. He failed the test, but said it was due to being nervous in court. Why did the officer fail to give my client the same excuse? NHSTA's manual claims that if the three SFST's are performed correctly and scored correctly, than they can have an accuracy rate of 91% for predicting a BAC of .08 or above. These studies are of questionable validity because they were all conducted by law enforcement agencies under unrealistic control, sample and verification conditions. It is important to emphasize that the 91% rate would only apply in a perfect investigation where the tests were done correctly. In the vast majority of cases, a good DUI defense attorney can find the defects to help undermine the value of this evidence in the prosecution's case. There are common misunderstandings of the role of FST's. Many people believe that FST's can show impairment or prove that a suspect has a certain blood alcohol level. The proper role of the FST's as testified to by the creator of the FST's is to help the arresting officer decide to arrest the DUI suspect and take the DUI suspect to have a chemical test performed. That is really the only purpose for FST's. Nevertheless, many prosecutors and others continue to insist that the test performance on its own is sufficient for conviction. It critical for the DUI defendant to obtain a DUI lawyer who understands the proper role and weaknesses of field sobriety tests and can effectively communicate these issues to juries and judges.
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