FIELD SOBRIETY TESTING – MORE THAN MEETS THE EYE

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.

FIELD SOBRIETY TESTING – MORE THAN MEETS THE EYE

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