Posted by: Phoenix Arizona DUI Attorneys
DUI lawyers have to contend with all manner of scientific evidence when defending drunk-driving cases. Juries hear from experts that the field sobriety tests the police conduct are valid and accepted. Except upon close examination, most of the field sobriety DUI tests have an accuracy rate only slightly better than a coin flip. Is this any way to prove a case beyond a reasonable doubt?Phoenix DUI attorney Nick Alcock says, “Absolutely not.”

“People have this idea that DUI field sobriety testing is fail safe and a very good indication of the general level of sobriety for a driver. Problem is that these tests don’t even work well in lab conditions. Even when you can control for lighting, temperature and level ground, these tests are terrible gauges of impairment.”

One of the most popular field sobriety tests is the Horizontal Gaze Nystagmus test, or HGN. HGN is a test where a police officer asks a subject to stare at a stimulus, such as the tip of a pen. Then the officer moves the pen laterally. The subject is instruction prior to the test to follow the stimulus with their eyes while keeping their head still.

The officer isn’t looking to see whether or not the subject is capable of looking at the pen. Instead, the officer is watching for tell-tale involuntary jerking of the eye muscles. This jerking is known as nystagmus. If the officer sees “smooth pursuit” of the stimulus, then the person passes the test. However, if the officer sees HGN, it can be used against the driver as a cue of impairment.

Recent studies, however have shown that nystagmus can be caused by a number of factors, including simple nutritional deficiencies. The National Institute of Health has documented numerous cases where nystagmus was treated with magnesium and thiamine supplements. (Go to www. It seems as if the validity of HGN field sobriety testing is in question.

Says DUI lawyer Alcock, “The more we learn about DUI investigations, the more we learn how shaky the science is. For years, the Intoxilyzer 5000, or breath testing machine, was viewed as the gold standard for alcohol testing. When people actually looked at the machine they realized that the source code had significant issues. Now jurisdictions around the country are quietly moving away from breath testing and towards blood draws. It seems that HGN is now just as suspect.”

If you have a DUI case in Phoenix or Arizona, please feel free to contact the DUI law firm of Alcock & Associates. An experienced DUI attorney can answer your questions right over the phone. 602-989-5000

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