Even if you have never undergone a field sobriety test, you are probably familiar with the concept from movies and T.V. In reality, however, field sobriety testing does not always look like it does in fiction.
Seeking a scientific measure of intoxication that would hold up in court, researchers developed a battery of three field sobriety tests in the 1970s, including standards for administering each. Today, authorities know these assessments collectively as the Standardized Field Sobriety Test. According to AAA, the SFST has an accuracy rate of 90%, and results are usually admissible in court. However, underlying medical conditions or disabilities can undermine the reliability of the test.
One-leg stand test
The one-leg stand test is one of two assessments in the SFST that gauges your ability to divide your attention between multiple simultaneous tasks. Alcohol can diminish this ability. During the one-leg stand test, you must start at 1,000 and count aloud by ones while holding your foot approximately six inches off the ground. The test lasts for 30 seconds, during which time a law enforcement officer observes you for signs of impairment such as putting your foot down, swaying or using your arms to balance.
This is another divided attention task. You must walk heel-to-toe along a straight line for nine steps, then turn around on one foot and return by walking in the same fashion. In addition to balance issues, law enforcement observes to see whether you follow instructions correctly.
Horizontal gaze nystagmus
This is not a divided attention assessment. Law enforcement asks you to keep your head still and follow a moving object with your eyes. The officer is examining your eyes for a specific pattern of involuntary jerking. This is a normal reflex but can become more pronounced under the influence of alcohol.