Field Sobriety Tests
Standardized Field Sobriety TestsGeorgia POST Certified Police Officers are trained on the (NHTSA) - National Highway Traffic Safety Administration standardized field sobriety testing (SFST) evaluations. The three standardized field sobriety tests are:
(1) The Horizontal Gaze Nystagmus,
(2) The Walk and Turn, and
(3) The One Leg Stand
Horizontal Gaze Nystagmus Evaluation (HGN)In conducting the Horizontal Gaze Nystagmus evaluation, the police officer is looking to see if 6 clues are observable in the suspect's eyes.
Horizontal Gaze Nystagmus is defines as the rythmic jerking of the eyes as they gaze to the side.
Prior to administration of this evaluation, the Officer must first medically qualify the suspect. The officer looks forst for resting nystagmus (ie: holding a stimulus at the center point of the suspect's field of vision, do the eyes exhibit rythmic jerking). The presence of resting nystagmus can indicate a medical issue or that a suspect is on PCP. The next thing that the officer checks for is equal pupil size and equal tracking. After completing this medical clearance, the officer then checks the suspects eyes for 6 clues (technically three things double for one clue in each eye). The officer checks for lack of smooth pursuit, distinct and sustaine nystagmus at maximum deviation and onset of nystagmus prior to 45 degrees.
The HGN Clues in more detail - Lack of Smooth PursuitLack of Smooth Pursuit
During the lack of smooth pursuit passes, the officer moves the stimulus at a speed of approximately two second out to the side and two seconds back to center. If the officer moves the stimulus too fast, some research indicate the officer may cause the eyes to give a false positive as the eyes can not track at greater than 30 degrees per second. In this phase, the officer is looking to see if the eyes pursue the stimulus smoothly (this would mean no observed clues) or if the eyes bounce as they pursue the stimulus (this would be an observable clue). Police instructors generally use the analogy of a windshield wiper on a piece of wet smooth glass - smoothly gliding over the glass vs. a windshield wiper on a dry windshield bouncing as it slides over the glass.
The HGN Clues in more detail - Distinct and Sustained Nystagmus at Maximum DeviationDistinct and Sustained Nystagmus at maximum deviation
The officer observes this clue by bringing the suspects eye out to the side as far as the eye will gaze (until there is no white left in the corner of the suspect's eye). The stimulus is then held in this position for a minimum period of 4 seconds. During this time, the Officer is looking to see if there is a distinct and sustained rythmic jerking of the eye back to center. If so then this is an observed clue.
The HGN Clues in more detail - Onset of Nystagmus prior to 45 degreesIn this phase the officer slowly moves the stimulus from the center out to the side (taking a minimum of 4 seconds to get to the 45 degree point (generally about the shoulder of the suspect). The officer is watching for the point when the rythmic jerking of the eye starts. Upon observation, the officer is supposed to make a brief confirmatory pause to insure that he is seeing the clue and then move back to the other eye.
HGN - What does it mean to the officerThe officer uses a scoring crietria for his arrest decision. If the officer sees 4 or more clues then this indicates a BAC of > .10 to a 77% reliability (meaning the officer is going to treat 4 or more clues as a "Yes" in the arrest decision tree.
Lack of smooth pursuit - 2 clues possible (one each eye)
Distinct and Sustained Nystagmus at Maximum Deviation - 2 clues possible (one each eye)
Onset of Nystagmus prior to 45 degrees - 2 clues possible (one each eye)
Walk and Turn EvaluationIn this test, the officer is using a divided attention test dividing the suspect's attention between multiple tasks to simulate the divided attention needed to drive. The test ultimately consists of walking 9 steps down an imaginary line, making a turn leaving the front foot planted and taking a series of small steps with the rear foot and taking 9 steps back up the line.
Initially the officer will have the suspect stand in an instructional position and have them remain that way until told to do otherwise. The officer will then explain the evaluation and demonstrate it. During this part of the test, the officer is looking to see if the suspect starts the test early or moves out of the start position.
The second phase of the evaluation is the walking portion. During this phase, the officer is looking to see if the suspect misses heel to toe, raises his arms for balance, stops walking to steady self, steps off the line, takes the wrong number of steps, or makes an improper turn.
One Leg Stand EvaluationThis is another divided attention test. Here the suspect's attention is divided between standing on one foot and counting. The officer has the suspect stand with their feet and knees together and arms down at their sides. Upon the instruction to begin, the suspect is asked to count 1001, 1002, 1003 and so on until told to stop. The evaluation lasts 30 seconds. The suspect is to lift one foot approximately 6 inches off the ground and point their toe so that the foot is parallel ot the ground.
The clues the officer is looking for are: (1) Puts Foot Down; (2) Uses arms for balance; (3) Sways; (4) Hops.
The arrest criteria for this test as well as for the Walk and turn test is observation of 2 or more clues.