DWI
Detection and Standardized Field Sobriety Testing
Session
7 – Phase Three: Pre-Arrest Screening
Vertical Gaze Nystagmus
Demonstration
7-12
D. Vertical Gaze Nystagmus – Definition, Concepts, Demonstration
Vertical
Gaze Nystagmus is an involuntary jerking of the eyes occurring as the eyes are
held
at maximum elevation.
For
VGN to be recorded, it must be distinct and sustained for a minimum of four
seconds
at maximum elevation.
Notes:_______________________________________________
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HS
178 R5/13 8 of 26
DWI
Detection and Standardized Field Sobriety Testing
Session
7 – Phase Three: Pre-Arrest Screening
Concentrating on more than one thing at a
time (mental tasks and physical tasks)
Divided Attention
7-13
E. Divided Attention Tests: Concepts, Examples, Demonstration
Many
of the most reliable and useful psychophysical tests employ the concept of
divided
attention:
they require the subject to concentrate on more than one thing at a time
(mental
tasks and physical tasks). Driving is a complex divided attention task. In
order to
operate
a vehicle safely, subjects must simultaneously control steering, acceleration
and
braking;
react appropriately to a constantly changing environment; and perform many
other
tasks.
Alcohol
and many other drugs reduce a person's ability to divide attention. Impaired
subjects
often ignore the less critical tasks of driving in order to focus their
impaired
attention
on the more critical tasks. For example, a subject may ignore a traffic signal
and
focus instead on speed control.
Even
when impaired, many people can handle a single, focused attention task fairly
well.
For example, a subject may be able to keep the vehicle well within the proper
traffic
lane as long as the road remains fairly straight. However, most people, when
impaired,
cannot satisfactorily divide their attention to handle multiple tasks at the
same
time.
The
concept of divided attention has been applied to psychophysical testing. Field
sobriety
tests that simulate the divided attention characteristics of driving have been
developed
and are being used by law enforcement agencies nationwide. The best of
these
tests exercise the same mental and physical capabilities that a person needs to
drive
safely.
Notes:_______________________________________________
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HS
178 R5/13 9 of 26
Standardized Field
Sobriety Testing
March 2013 Edition
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