DWI – Physical & Mental Tests


There are 3 “standardized” tests that police officers give in order to determine if they have probable
cause to arrest a person for DWI. They also give other tests, but they are not the “standardized” tests.
The three tests are
1) the HGN (Horizontal Gaze Nystagmus test),
2) the Walk and Turn, and
3) the One Leg Stand.

1) HGN: Horizontal Gaze Nystagmus. This test is used to see if your eyes jerk involuntarily when following an object. The police are trained that if a person’s eyes do exhibit this jerk (nystagmus), this is a sign of intoxication. The test must be administered properly to obtain an valid result.

2) Walk and Turn: This test is designed to evaluate the subjects mental and physical faculties. You are given a series of instructions, and if you vary from the instructions, police are trained to use these deviations from the instructions as evidence of intoxication. The instructions you are given are to do a physical task (basically, walk the straight line, turn and walk back). It sounds simple, but the instructions are designed to make this a very unnatural type of walk. If you are unable to walk and turn in exactly the way the officer asks you to walk and turn, the officer is trained to see this as evidence of intoxication.

3) One Leg Stand : This is a similar test to the Walk and Turn, in that it has a physical and mental portion. They test your mental faculties by once again, seeing if you can follow their directions. They test your physical faculties by observing whether you can actually perform the test. On the physical part of the exam, they look for swaying, using arms for balance, hopping, placing a foot down before 30 seconds expire. Unfortunately for the test subjects, they are not told that they will be graded off for these things.