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.
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.
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.
Several field sobriety tests require divided attention because they require the subject to complete two or more tasks at the same time. For example:
Other times, two different field sobriety tests may be combined with each other. For example:
There are also three questioning techniques that look for divided attention. These techniques are: