The three most commonly used field sobriety evaluations are the Horizontal Gaze Nystagmus Test, or eye jerking test, the nine step walk and turn, and the 30-second one leg stand. These tests supposedly correlate specific clues with blood alcohol levels, but not “impairment” as so often testified to by police on the witness stand.
These tests were validated by NHTSA in the 1970’s in a controlled environment using a cross-section of the population and found that they are reliable around 70% of the time. Other non-controlled studies have been done with higher percentages, but they have been by police and in the field after midnight, which tends to focus on a much narrower cross section of the population.
HGN is naturally present in approximately 10% of the population without the presence of alcohol. Medical disorders such as inner ear infections, vertigo, water in the ear and Meniere’s Disease can cause the eye to jerk or HGN as if alcohol had been ingested. DUI police officers tend to use more than the standardized number of passes for the HGN test and move the pen or target object back and forth several times more. They claim to be making sure they are performing the entire test, but in reality they are actually inducing eye jerking or HGN.
Most police officers can’t even name the muscles of the eye that they are testing during HGN. The HGN tests the lateral and medial rectus muscles as well as the cranial nerves that innervate the muscles. The 6th cranial nerve, or the abducens, is tested by the HGN procedure. These muscles are like “rubber bands” and easily fatigue and begin to spasm or “jerk” when over-stimulated. That, of course, is the same HGN produced by alcohol ingestion.
The Nine Step Walk and Turn and the One Leg Stand are divided attention dexterity tests. These tests are easier to do with practice. The first time you try them, they are often impossible, regardless of whether you have been drinking. Just ask them about how long it took them to learn to ride their bicycles, ice skate, roller skate or perform yoga balancing moves. Many athletic activities require practice and frequent repetition in order to perform fluidly, which has no relation to alcohol consumption.
The Romberg test is another sobriety evaluation that is misunderstood and misapplied by police in DUI investigations. In the Romberg test, the subject is asked to stand with feet together, tilt the head back slightly, close the eyes, and estimate 30 seconds. The Romberg Test is a test for Upper Motor Neuron disease. Many older adults will fall over when performing this test without the presence of alcohol.
We encourage our juries to try these tests back in the jury room so they can see how easy they are to fail.