The eyes have it

At the side of the road, law enforcement routinely makes DUI arrests based upon results of a Horizontal Gaze Nystagmus (HGN) test. The underlying premise of the test is: you drink enough alcohol, and then you eyes will show HGN.

Alcohol, however, is not the sole cause of HGN. In State v. Horn, the court recognized the following causes or possible causes of HGN:

  • problems with the inner ear labyrinth;
  • irrigating the ears with warm or cold water;
  • influenza; streptococcus infection;
  • vertigo;
  • measles;
  • syphilis;
  • arteriosclerosis;
  • Korchaff's syndrome;
  • brain hemorrhage;
  • epilepsy;
  • hypertension;
  • motion sickness;
  • sunstroke;
  • eye strain;
  • eye muscle fatigue;
  • glaucoma;
  • changes in atmospheric pressure;
  • consumption of excessive amounts of caffeine;
  • excessive exposure to nicotine; aspirin;
  • circadian rhythms;
  • acute head trauma;
  • chronic head trauma;
  • some prescription drugs; tranquilizers,
  • pain medication,
  • anti-convulsant medicine;
  • barbiturates;
  • disorders of the vestibular apparatus and brain stem;
  • cerebellum dysfunction;
  • heredity;
  • diet;
  • toxins;
  • exposure to solvents;
  • extreme chilling;
  • eye muscle imbalance;
  • lesions;
  • continuous movement of the visual field past the eyes; and
  • antihistamine use.


What Do Field Sobriety Tests Prove?

The short answer is not much. At best, they may correlate to someone having a blood alcohol concentration over a .08. At worst, they prove nothing at all. To understand their meaning you must look at how they came into existence and who developed them.

In the late 1970’s, NHTSA (the National Highway Traffic and Safety Administration) paid for some research to see if tools could be developed for law enforcement to identify people who are potentially DUI / DWI.

There were several studies paid for by the government. Specifically, there are six primary studies relied on by law enforcement. However, none of the studies have been subject to peer review.

1977 Study (Not Peer Reviewed)

1981 Study (Not Peer Reviewed)

1983 Study (Not Peer Reviewed)

Colorado Study (Not Peer Reviewed)

Florida Study (Not Peer Reviewed)

San Diego Study (Not Peer Reviewed)

According to Wikipedia, peer review has been defined as:

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This Video Demonstrates True Field Sobriety Testing

In case you ever wondered what happens on the side of the road when a person is stopped for DUI, here is a video showing exactly what goes on.  Enjoy:


DUI Stop from konu on Vimeo.

Imaginary DUI?

When police officers are attempting to determine whether to arrest someone for driving under the influence of alcohol (DUI), they usually ask them to perform some field sobriety tests.  Police generally rely on a battery of tests recommended by the National Highway Traffic Safety Administration (NHTSA).  One of these tests is referred to as the "Walk-and-Turn" test.  The instructions for performing the Walk-and-Turn test are contained in the NHTSA DWI Detection and Standardized Field Sobriety Testing Manual.

In essence, the Walk-and-Turn test requires that a person walk a straight line, touching heel to toe, and then turn around and walk back.  However, it seems many officers in Arizona (and apparently in other states as well) believe that using an imaginary line is a fair test.  That is, instead of having a person walk on a true line (i.e. a painted line in a parking lot) they have the person imagine a line to walk on.  Just this morning I was debating this issue with a Scottsdale Police Officer in a DUI case.

Austin, Texas DWI lawyer Jamie Spencer has written an excellent article entitled, Walking A Straight Line, arguing the merits of using an imaginary line during a Walk-and-Turn test.  He writes:

One common misconception that I see over and over on the part of officers, up to and including some of the local Austin DWI task force officers, is the belief that the book doesn’t require that a designated actual line be used.

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Introducton to Field Sobriety Testing

Field sobriety tests are any one of several roadside tests that can be used to determine whether a suspect is impaired.  These psychophysical tests are performed on DUI suspects to assist an officer in the decision to make an arrest.  In theory, these tests directly assess impairment by focusing precisely on the human capabilities needed for safe driving. 

The procedures for conducting field sobriety tests are put forth by the National Highway Traffic Safety Administration (NHTSA).  NHTSA is a federal agency charged with reducing deaths and injuries from motor vehicle crashes.  They also attempt to fight drunk driving.  The are responsible for the field sobriety testing guidelines.  They base their procedures on scientific studies.  However, NHTSA does not conduct their own studies.  Rather, the studies are done by those who write grant proposals and are given monetary compensation.  Moreover, none of the studies  supporting the NHTSA Standardized Field Sobriety Testing Manual are "peer reviewed."  This is the process of subjecting an author's scholarly work, research or ideas to the scrutiny of others who are experts in the same field.