One form of evidence that is often used against DWI defendants is the results of their field sobriety tests. In order to evaluate drivers for intoxication, law enforcement rely on field sobriety tests to measure suspects' physical impairment. In 1977 The National Highway Traffic Safety Administration (NHTSA) commissioned a study to determine the best and most accurate forms of field sobriety tests. The researchers found that 3 tests (the walk and turn test, the one leg stand test and the horizontal gaze nystagmus test) proved to be the most accurate at predicting driver impairment. In 1981, these 3 tests were established as Standardized Field Sobriety Tests or SFSTs. SFSTs are commonly used by police to gauge the sobriety of DWI suspects. While chemical testing is the most reliable way of measuring intoxication, many feel that the Horizontal Gaze Nystagmus (HGN) test is the most accurate of the SFSTs because it is the only one that relies on science.
According to an article from the NHTSA about the science and laws surrounding HGN tests, nystagmus is an involuntary jerking of the eyes that occurs when there is an imbalance in the inner ear or a person's motor skills are impaired. Horizontal gaze nystagmus refers to the jerking of the eyes that an officer can observe while a suspect is moving their eyes side to side. When a person consumes alcohol or certain drugs, they will often demonstrate nystagmus. Horizontal gaze nystagmus is popular among law enforcement because it is a relatively easy way to spot impairment. It also is more scientific then other field sobriety tests which rely on suspects performing physical tasks to show whether their motor skills are impaired.
How HGN Tests Are Performed
When a law enforcement officer stops a driver and suspects that they are intoxicated, the officer will often ask them to perform a SFSTs. To perform a horizontal gaze nystagmus test, the officer will first direct the suspects to follow an object such as a pen or the tip of a finger think with their eyes as they move it from side to side across the suspect's field of vision. The suspect cannot move their head and must follow with their eyes only. While performing this test, the officer is trained to look for 6 clues of impairment. These are made up of 3 cues that are looked for in both eyes. These cues include the following:
Lack of smooth pursuit – During the test, both eyes should be able to follow the object smoothly without jerking or bouncing (nystagmus) while it is passed side to side across the driver's field of vision. The officer will check each eye for any sign of this and will consider any sign of nystagmus to mean the driver is impaired.
- Distinct nystagmus at maximum deviation – After moving the object side to side, the officer will move the object to the far left and then to the far right of the suspect's field of vision and hold it there for at least 4 seconds. The purpose of this is to get the suspect to move their gaze as far to the left and then the right as possible and then hold it there. In this position, signs of nystagmus are often most obvious.
Angle of onset of nystagmus prior to forty-five degrees – This is the most complicated clue for officers to observe. It involves the officer looking to see if the suspect displays signs of nystagmus before the object reaches 45 degrees from the middle of their face. Officers do not use any device to measure this and rely only on their own opinion.
Nystagmus Test Defense Options
Though HGN tests are scientific and often believed to be a good way of determining impairment in a driver, arrests that result from failing such tests are not do not mean you are automatically guilty. If you have been arrested for DWI in New Hampshire after failing a field sobriety test, you have defense options. The experienced DWI attorneys Russman Law have a deep understanding of field sobriety tests and how they should be performed. Law enforcement officers, for example, must be properly trained to perform this test and must ask prior to administering the test if the suspect has any medical issues that could affect the results. If the officer makes any error while performing a horizontal gaze nystagmus test, your attorney may be able to challenge the validity of the results. To find out more about fighting your NH DWI charges, contact our office right away.