Arrest and Processing

Field Sobriety Tests

What Are Field Sobriety Tests?

Field Sobriety Tests (FST’s) are psycho-physical tests used to assess a person’s physical and/or mental impairment. These tests focus on the abilities needed for safe driving. Most of the more reliable psycho-physical tests are known as “divided attention” tasks. They require a person to concentrate on more then one task at the same time. To safely drive a car, a person needs to be able to simultaneously control steering, breaking, and acceleration; react to constantly changing driving environment; and perform many other tasks.

Alcohol affects one’s ability to adequately divide attention, thus causing drivers to concentrate on more difficult tasks while ignoring simpler ones (i.e. ignore a traffic signal while concentrating on one’s speed). Even if impaired, most people can successfully concentrate on a single task fairly well, but when impaired, most drivers cannot successfully divide their attention between multiple tasks at once.

Divided attention tasks are designed to evaluate mental and physical capabilities a person needs to safely drive a car. They include information processing; short-term memory; judgment and decision making; balance; steady, sure reactions; clear vision; small muscle control; and coordination of limbs. A good FST will combine any two or more of these capabilities simultaneously. A test must also be reasonably simple for the average non-intoxicated person to perform.

The most common FST’s used by the police include the three standardized tests consisting of the Horizontal Gaze Nystagmus tests, Walk & Turn test, and the One Leg Stand test. These three tests have been validated as reliable indicators of intoxication, although they are not 100% accurate. Other commonly used, but non-standardized, tests include counting backwards, saying the alphabet (or a portion of it), finger count, and the stationary balance (Rhomberg) tests.

In reference to the three standardized FST’s, the government has admitted, and it is printed in the police officers DWI manual, that “IT IS NECESSARY TO EMPHASIZE THIS VALIDATION ONLY APPLIES WHEN: THE TESTS ARE ADMINISTERED IN THE PRESCRIBED STANDARD MANNER; THE STANDARDIZED CLUES ARE USED TO ASSESS THE SUSPECTS PERFORMANCE; THE STANDARDIZED CRITERIA ARE EMPLOYED TO INTERPRET THAT PERFORMANCE. IF ANY ONE OF THE STANDARDIZED FIELD SOBRIETY TEST ELEMENTS IS CHANGED, THE VALIDITY IS COMPROMISED.”

Horizontal Gaze Nystagmus (HGN)

This test refers to the involuntary jerking of the eye as it gazes to the side. When this occurs, the person is unaware of the jerking, and cannot control it. This involuntary jerking becomes noticeable as persons’ blood alcohol increases. This is the most reliable of the FST’s. However, nystagmus is a natural, normal phenomenon. Alcohol and certain drugs do not cause this phenomenon.

When the HGN test is administered, the officer hold a stimulus (usually a pen) 12-15 inches in front of you eyes and asks you to follow the stimulus with your eyes, without moving your head. The officer will always start with the left eye and they are looking for 3 specific clues:

  1. Lack of Smooth Pursuit: As the eye moves from side to side, does it move smoothly or does it noticeably jerk (bounce)? The jerking is similar to how windshield wipers jerk across a dry windshield. There is a standardized pace the officer is to have the eyes move side to side. From the center of the face, they are to move the eye all the way out to the side in approximately 2 seconds, then 2 seconds back to center, approximately 2 seconds to the other side, and 2 seconds back to center. They are to repeat the procedure. If they have the eyes move too fast, not only are they performing the test improperly, the government has admitted that quick movement of the eyes may cause nystagmus.
  2. Distinct Nystagmus at Maximum Deviation: When the eye moves as far to the side as possible and is kept in that position for several seconds, is there distinct jerking (bouncing) of the eye. The eye is to be moved all the way to the side, and kept there a minimum of 4 seconds. Interestingly enough, some people exhibit slight jerking of the eye at maximum deviation even when unimpaired! Also, if the eye is moved to the side too quickly, this may cause the nystagmus.
  3. Onset of Nystagmus Prior To 45 Degrees: As the eye moves towards the side, does it start to jerk (bounce) before it reaches a 45-degree angle? When moving the eye out to 45-degree’s, the movement of the eye should take approximately 4 seconds to reach 45-degrees. It is important to take the full 4 seconds when checking for onset. If the stimulus is moved too fast, the officer could take your eye beyond 45 degrees, or if the eye is moved to 45-degrees too quickly, this may cause the nystagmus. The maximum number of clues in each eye is 3, for a total of 6 clues. The original research has shown that if 4 or more clues are present, the person is intoxicated. This test has been shown to be accurate 77% of the time; therefore, it is inaccurate 23% of the time!

Walk and Turn

This divided attention test consists of the instruction phase and the walking phase. During the instruction phase, the person must stand with the right foot directly in front of the left foot with the heel and toes touching, keeping their arms at their side, while listening to the instructions. One’s attention is divided between keeping their balance and listening to and remembering the instructions. The instruction phase of the test takes at least 45 seconds to complete. If you use yours arms for balance in this awkward position of step out of the position, it will be taken as a sign of intoxication.

During the walking phase, the person takes 9 heel-to-toe steps, turns in a prescribed manner, take 9 heel-to-toe steps back, while counting the steps out loud. The steps are taken down a straight line, and if an actual line is not present, the person is instructed to walk down an imaginary line. The walking phase divides a person’s attention between keeping their balance, counting out loud, taking the proper number of steps, turning in the prescribed manner, while keeping their arms at their side.

The officer is looking for 8 specific clues:

  1. Can’t balance during instructions
  2. starts too soon
  3. stops while walking
  4. doesn’t touch heel-to-toe
  5. steps off line
  6. uses arms for balance
  7. loses balance on turn or turns incorrectly
  8. takes the wrong number of steps

The original research has shown that if 2 or more clues are present, the person is intoxicated. This test has been shown to be accurate 68% of the time; therefore, it is inaccurate 32% of the time!

One Leg Stand

This divided attention test consists of the instruction phase and the balance & counting phase. During the instruction phase, the person must stand with their feet together, keeping their arms at their side while listening to the instructions. One’s attention is divided between keeping their balance and listening to and remembering the instructions.

During the balance and counting phase, the person must raise one leg approximately 6 inches off the ground, arms at their side, toes pointed out and looking at the pointed toes, and keeping both legs straight. While looking at their toes, they are to count 1001, 1002, 1003, etc. until they are told to stop. The test is to last for 30 seconds and the officer is supposed to time the test. During the test, if at anytime a person puts their foot down, they are instructed to pick it back up and continue counting where they left off.

The officer is looking for 4 specific clues:

  1. sways while balancing
  2. using arms for balance
  3. hopping
  4. putting foot down

The original research has shown that if 2 or more clues are present (i.e. putting foot down 1 time and having a couple seconds of sway), the person is intoxicated. This test has been shown to be accurate 65% of the time; therefore, it is inaccurate 35% of the time!

Counting Backwards (not a validated test)

This divided attention test requires a person to count out loud a set of numbers in reverse order. For example, the person is instructed to count starting with 56 and ending with 28. This divides the person’s attention because they have to remember what number to start with, count backwards correctly, and remember what number to stop on. Anything other than 100% perfection will be viewed as a sign of intoxication.

Alphabet (not a validated test)

This test requires a person to recite a portion of the alphabet. For example, the person is instructed to start with a specific letter, D, and stop at a specific letter, T. This divides the person’s attention because they have to remember the specific letter to start with, say the letters in sequence, and remember the letter to stop with. Anything less than 100% perfection will be viewed as a sign of intoxication.

Finger Count (not a validated test)

This test required a person to touch the tip of each finger in succession to the tip of their thumb, up and back, while counting 1, 2, 3, 4, .. 4, 3, 2, 1. They must touch fingertips while not counting out of order. Anything less then 100% perfection will be viewed as a sign of intoxication.

Stationary Balance (i.e. Rhomberg) (not a validated test)

This test requires a person to stand with heels and toes touching, leaning their head back to look up at the sky or ceiling, holding their arms out to the side (like an airplane) and estimate 30 seconds. The officer is looking for any unnatural sway. I have had officers testify from a range of anything more than ½ inch to 1 inch from center is too much sway and must be caused by intoxication. Also, if your estimation is not close to 30 seconds, this will be viewed as a sign of intoxication.

Try these Field Sobriety Tests at home with someone evaluating you and contact me with your results.

Being sober, how many tests did you fail?

Even though officers have testified that all non-intoxicated people should be able to successfully perform Field Sobriety Tests (i.e. 100% accurate), the National Highway Traffic Safety Administration, through their extensive research, has acknowledges that: – these tests lose their sensitivity if repeated;- sober people have difficulty with balance;- leg problems can affect these tests;- back problems can affect these tests;- middle ear problems can affect these tests;- weight can affect the tests;- age can affect the tests;- footwear can affect theses tests; and- weather conditions can affect the tests.