All field tests are preceded by interrogation
Regardless of which field sobriety test is used, the test is generally preceded by an interrogation of the person to be tested. The interrogation itself is a form of a test because it provides the officer an initial opportunity to look for “objective” signs of intoxication such as the odor of alcohol or slurred speech.
Justification for interrogation
Part of the reason for questioning a subject before giving a field sobriety test is to determine whether the person has any preexisting physical impediments that would preclude using a particular field sobriety test.
For example, if a person has bad knees, field sobriety tests requiring balancing on the legs should not be given.
Also, a general sense of whether the person is suffering any mental impairment from alcohol can be revealed by asking the person in the field to tell the officer what the date and time is. Questioning the person why they were stopped by the police has the same goal as asking the date and time.
Justification for divided attention tests
Another reason for pre-field sobriety test questioning is to assess the divided attention ability of the person to be tested.
Divided attention is the term given to the process by which the brain must perform two or more tasks at the same time. With alcohol use, the task becomes more difficult. Divided attention tasks are expected to show some decrease in ability (without driving impairment) at very low levels.
The theoretical justification for divided attention tests is that they test the ability to perform the type of mental and physical multitasking that is required to operate an automobile.
Using tests and questions that require divided attention
Several field sobriety tests require divided attention because they require the subject to complete two or more tasks at the same time. For example:
- The walk-and-turn test requires the subject to perform a difficult physical task while listening to and comprehending compound instructions.
- The one-leg stand test requires the subject to balance on one foot while at the same time counting aloud in thousands.
Other times, two different field sobriety tests may be combined with each other. For example:
- A count aloud test may combine the count with the touching of the thumb to the fingertips (the finger count test).
- Walking a straight line may be combined with touching the heel to the toes (the walk and turn test).
There are also three questioning techniques that look for divided attention. These techniques are:
- Ask for two things simultaneously. For example, ask for both a driver’s license and the car registration.
- Ask interrupting or distracting questions.
- Ask unusual questions.