Field Sobriety Test Flashcards
HGN Testing
The examiner looks for three indicators of impairment in each eye:
- if the eye cannot follow a moving object smoothly
- if jerking is distinct when the eye is at maximum deviation.
- and if the angle of onset of jerking is within 45 degrees of center.
- If, between the two eyes, four or more clues appear, the suspect likely has a BAC of 0.08 or greater.
NHTSA research found that this test allows proper classification of approximately 88 percent of suspects (Stuster and Burns, 1998). HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.
!
Walk and Turn
-Walk-and-Turn test and One-Leg Stand test
The Walk-and-Turn test and One-Leg Stand test are “divided attention” tests that are easily performed by most unimpaired people. They require a suspect to listen to and follow instructions while performing simple physical movements. Impaired persons have difficulty with tasks requiring their attention to be divided between simple mental and physical exercises.
The examiner looks for eight indicators of impairment:
- if the suspect cannot keep balance while listening to the instructions,
- begins before the instructions are finished,
- stops while walking to regain balance,
- does not touch heel-to-toe,
- steps off the line, uses arms to balance,
- makes an improper turn,
- takes an incorrect number of steps.
Studies by Stuster and Burns, 1998
NHTSA research indicates that 79 percent of individuals who exhibit two or more indicators in the performance of the test will have a BAC of 0.08 or greater (Stuster and Burns, 1998).
One Leg Stand
!
The officer looks for four indicators of impairment, including
- swaying while balancing,
- using arms to balance,
- hopping to maintain balance,
- and putting the foot down.
Study by STuster and Burns, 1998
NHTSA research indicates that 83 percent of individuals who exhibit two or more such indicators in the performance of the test will have a BAC of 0.08 of greater.
Comparison of SFST Accuracies 1981 vs. 1998
!
Study: Combined Tharp, Burns, & Moskowitz (1981)
BAC: 0.10
HGN: 77%
WAT: 8%
OLS: 65%
Combined: 81%
Study: Stuster & Burns (1998)
BAC: 0.08
HGN: 88%
WAT: 79%
OLS: 83%
Combined: 91%
NHTSA
National Highway Traffic Safety Administration
These field sobriety tests
are considered standardized,
because the tests are administered using the
same instructions regardless of who is administering the tests.
Walk and Turn/ One Leg Stand
Pursuant to these studies, two or more
errors on either the one-leg stand or the walk-and-turn indicate that an officer will correctly predict an alcohol concentration at or above a 0.08 with
a high degree of accuracy.
HGN
Horizontal Gaze Nystamus
HGN
Four or more cues on the HGN test are
consistent with having an alcohol concentration at or above a 0.08.
“Nystagmus” means
an involuntary jerking of the eyes.
Horizontal Gaze Nystagmus (HGN) refers to
an involuntary jerking
occurring as the eyes gaze toward the side.
HGN
As a person’s blood alcohol concentration increases, the eyes will begin to jerk sooner as they move to the side.
HGN
When the HGN test is administered always begin with subject’s left eye.
Each eye is examined for three specific clues.
Clues
!. as the eye moves from side to side, does it move smoothly or does it jerk
noticeably? (As people become impaired by alcohol, their eyes exhibit a
lack of smooth pursuit as they move from side to side.)
Clues
- when the eye moves as far to the side as possible and is kept at that
position for several seconds, does it jerk distinctly? (Distinct and sustained
nystagmus at maximum deviation is another clue of impairment.)
Clues
as the eye moves toward the side, does it start to jerk prior to a 45-
degree angle? (Onset of nystagmus prior to 45-degrees is another clue of
impairment.)
The maximum number of clues that may appear in one eye is
3
The maximum total number for any suspect is
6
The original research shows that if four or more clues are evident,
it is likely that the suspect’s blood alcohol concentration is above 0.10. With four-or-more clues present, this test is 77% accurate.
VERTICAL GAZE NYSTAGMUS
Although this type of nystagmus was not addressed in the original research, field experience has indicated that the presence of Vertical Gaze
Nystagmus has proven to be a reliable indicator of high doses of alcohol for that individual or certain other drugs.
divided attention:
they require the subject to concentrate on two
things at once.
Walk and Turn:
8 Clues
o can't balance during instructions; o starts too soon; o stops while walking; o doesn't touch heel-to-toe; o steps off line; o uses arms to balance; o loses balance on turn or turns incorrectly; and, o takes the wrong number of steps.
Inability to complete the Walk-and-Turn test occurs when the suspect:
o steps off the line three or more times;
o is in danger of falling;
o cannot do the test.
Original research shows that if a suspect exhibits two or more of the clues,
or cannot complete the test, the suspect’s BAC is likely to be above 0.10.
This criterion has been shown to be accurate 68 percent of the time.
ONE-LEG STAND
It is a divided attention test consisting of two stages:
o Instructions Stage; and,
o Balance and Counting Stage.
In the Instruction Stage, the subject must stand with feet together, keep
arms at sides, and listen to instructions.
This divides the subject's attention between a balancing task (maintaining a stance) and an information processing task (listening to and remembering instructions.)
Officers carefully observe the suspect’s performance and look for four specific clues:
o sways while balancing;
o uses arms to balance;
o hops;
o puts foot down.
Inability to complete the One-Leg Stand test occurs when the suspect:
- puts the foot down three or more times, during the 30-second period;
- cannot do the test.
The original research shows :
when the suspect produces two or more
clues or is unable to complete the test, it is likely that the BAC is above 0.10. This criterion has been shown to be accurate 65 percent of the time.
