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This article is a continuence of my earlier articles on Driving Under the Influence offense in Fresno ca and other parts of California.  As a Former Probation Officer DA and a Criminal Defense Attorney with more than 14 years of experience I have the knowlege to properly represent you in your criminal case or DUI case.  I have both the experience of prosecuting and defending DUI cases.  If after reading this blog bost or others you need help don't hesitate to call 559 441-1418. 

  In my earlier blog post I went over the non standardized testing to determine if there is probable cause to arrest for a Driving Under the Infuence. 


When an officer asks a driver to exit a vehicle, the officer is trained to look for the following additional specific signs of impairment.


unusual instructions

cant open the door

leaves car in gear

climbs out car

leans against car

keeps hands on car


Officers administer the three psychological field sobriety tests.  Psychological tests are methods of assessing a persons mental (psychological) and physical impairment.  Most psychological tests use the concept of divided attention to assess a persons impairment. 

Field sobriety tests that simulate the divided attention characteristics of driving have been developed and are being used by law enforcement agencies nationwide. 

These tests attempt to simulate the same mental and physical capabilities that a person needs to drive safely. 

information processing

short term memory

judgment and decision making


steady sure reactions

clear vision

small muscle control

coordination of limbs



The three Standardized Field Sobriety Tests tha tthe police use are the Horizontal Gaze Nystagmus (HGN) test, the Walk and Turn Test, and the One Leg Stand Test. 

The Horizontal Gaze Nystagmus test is administered first.  This test is considered to be the most reliable of the three standardized tests the police are  trained to do.  The police are trained that it is 77 percent accurate for people above the level of .10. 

Nystagmus is defined by the involuntary jerking of the eyes.  Nystagmus is a natural and and normal phenomenon.  Alcohol and certain drugs do not cause this effect.  They merely exaggerate or or magnify the effect. 

There are over 40 different kinds of Nystagmus and many of them look the same as the Horizontal Gaze Nystagmus that the police are looking for as evidence of impairment.

The police are not trained to distinguish between different kinds of Nystagmus.  However, some officers will testify that they are. 

it is common for the officer to misdiagnose some other form of bystagmus.  Call it Horizontal Gaze Nystagmus, and use it as evidence against a  person.


There are three general categories of Nystagmus:



Pathological Disorders and Disease. 

Vestibular Nystagmus

Vestibular Nystagmus is caused by the movement of or action of the vestibular (inner ear)  system. 

Rotational Nystagmus occurs when a person is spun around or rotated rapidly, causing the fluid in the inner ear to be disturbed.  If it were possible to observe eyes of a rotating person, they would be seen to jerk noticeably. 


Post rotational

nystagmus is a closely related to rotational nystagmus when the person stops spinning the fluid in the inner ear remains disturbed for a period of time. , and the eyes continue to jerk.  This could be observed in a person after a rollover accident or a spin out. 


nystagmus occurs when the fluid motion in the cannals of the vesibular system is stimulated by temperature (cold in one ear and warm in another). 

positional alcohol nystagmus (pan) occurs when a foreign fluid such as alcohol that alters the specific gravity of the blood is unequel concentrations in the blood and vestibular systems. 


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Gerald Schwab, Jr.


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Fresno Criminal Defense Attorney
5588 N Palm Ave,
Fresno, CA 93704
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Phone: 559.441.1418