The point of the field sobriety test is to test for a person’s physical and mental impairment. This is known as a Divided Attention Test. Essentially, the test is set up to test whether one is mentally capable of following the directions that are given by the police officer and whether the individual is capable of physically carrying out those instructions.
For example, if the officer instructs the motorist to take ten steps forward and then do a 180-degree turn to the right, the officer is not simply testing whether a person can walk and turn without tripping, but whether the person also has the presence of mind to walk exactly ten steps, and whether that person turns to the right as they were told. A person who forgets the directions given by the officer may be considered mentally impaired by the officer on the basis that they can’t follow simple directions.
The prosecution will try to make any failure to listen to directions or any failure to carry out the directions without stumbling, tripping, or falling as signs that a person was under the influence. A skilled DUI / DWI defense attorney will be able to make sense of those failures and paint them as normal actions having nothing to do with being intoxicated. Perhaps a person has poor hearing or inherently bad balance which can account for any problems during a field sobriety test.
Once again, in California there is the per se law that says that anyone with a blood alcohol content of .08 percent or greater is considered, by law, too drunk to drive, and there is the second law which states that it is illegal to drive under the influence of alcohol. It is in this case that the prosecution will seek to use the field sobriety test as circumstantial evidence of a person’s intoxication.
One should bear in mind that although police use the field sobriety tests to gather evidence against a motorist suspected of drunk driving, in California, the field sobriety tests are optional even though most police officers won’t tell that to a suspect.
While the field sobriety test is used to determine both the motorist’s physical and mental impairment, it should be remembered that experts on both sides of the law agree that mental impairment will always precede physical impairment. Physical impairments are not necessarily rooted in mental impairments. Fragile bones or an old soccer injury can cause just as much, if not more, physical impairment than alcohol.
Other factors that may result in physical impairment can be drowsiness, nervousness, or perhaps the threat of going to jail for the night. It is the job of a qualified DUI / DWI Defense lawyer to do a thorough investigation into clients’ histories to determine if any of the above factors may have been the cause of physical impairment instead of alcohol.
Furthermore, a person with a high tolerance for alcohol, though they might be mentally impaired, may be able to disguise that impairment by carrying out the physical part of the field sobriety tests without any problems. Disguising mental symptoms of impairment is not as simple, or even possible.
In performing field sobriety tests for DUI / DWI cases, the National Highway Traffic Safety Administration has “validated” three tests in particular. These tests are the Horizontal Gaze Nystagmus Test, the Walk-and-Turn Test, and the One-Leg-Stand Test. These tests have standard instructions for the motorist to follow and they have standard scoring for the police officer to use in the evaluation of the motorist’s performance.
There are other non-standardized tests that may also be used by the police. They are, the finger-to-nose test, reciting the alphabet, the finger tap test, the hand pat test, and the Rhomberg balance test, among other things a police officer may use to determine a motorist’s impairment.
At the end of the day, no matter how a driver being prosecuted for a DUI / DWI feels he or she performed on a field sobriety test, a drunk-driving defense attorney with years of experience can use the results of the tests to demonstrate that any physical impairment came from sources other than alcohol.