Horizontal Gaze Nystagmus: Police Rely on It – Courts Do Not!

Police officers in Massachusetts are trained to use several techniques to determine whether drivers are under the influence of alcohol, including field sobriety tests. Field sobriety tests are exercises officers may ask a driver to perform at roadside that give the officer a chance to see how well that person is able to control their body and follow instructions. Officers are trained to look for particular clues during each test that may indicate whether the driver is under the influence of alcohol.

What is the Horizontal Gaze Nystagmus Test?

The Horizontal Gaze Nystagmus (HGN) is a field sobriety test officers nationwide are trained to use. During the HGN, the officer asks the driver to stand still at roadside, and holds an object like a pen or pencil 12-15 inches in front of their face. The officer then asks the driver to look at the object without moving their head as the officer moves it laterally in front of the driver’s face.

When a person looks to the side without moving their head, their eyeballs will involuntarily vibrate at the far reaches of their range of motion. An onlooker paying attention can see it. This phenomenon is known as “nystagmus.” It’s believed that, when a person is under the influence of alcohol, this vibration will begin before the person’s eyes have turned 45 degrees to the left or right. According to police training materials, nystagmus is more apparent as a person’s blood alcohol content is increased.

Among other clues, officers are trained to look for:

The HGN is Inadmissible at Trial

Officers are trained to believe that the HGN is more reliable than any other field sobriety test. Nevertheless, in Commonwealth v. Sands , the court ruled that police officers are not allowed to testify about their use of the HGN unless they’re certified as an expert witness. Expert certification is needed before anyone can testify about subjects beyond the common knowledge or understanding of jurors, who are not expected to have any particular scientific training.

In over a decade of practicing law, I have never even heard of a police officer in Massachusetts being certified as an expert witness for purposes of the HGN, and so the test has no practical influence on the outcome of trials. In fact, I have never even heard of a district attorney’s office that tried to prove that a police officer is an expert on the HGN.

Massachusetts Police Still Use the HGN to Investigate OUI

Even though the test may not be used at trial, police officers in Massachusetts can and do continue to rely on it during their investigations into operating a motor vehicle while under the influence of alcohol.

You Don’t Have to Agree to Take Any Field Sobriety Test, Including the HGN!

Massachusetts’ constitution includes many protections, including the privilege against self-incrimination – the same right that allows us to remain silent. In Commonwealth v. Brown , the court ruled that drivers have the right to refuse to cooperate with police officers’ demands to take field sobriety tests. Importantly, the prosecutor can’t later argue at trial that the driver refused to cooperate because he knew he was under the influence of alcohol.

Knowing this, it’s hard to imagine why anyone in Massachusetts would agree to take the HGN – or any other field sobriety test.

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