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The Myth of a Twitchy Eye – HGN

Every working day in courts throughout the land, some version of this testimony is elicited from prosecutors:

Q: And what is Horizontal Gaze Nystagmus?

Officer: “Horizontal Gaze Nystagmus is the involuntary jerking of the eyeballs. Imagine a ball traveling over a smooth surface. That’s how the eye should move. But when someone’s consumed alcohol, the eye will jerk – like it’s moving over sandpaper.”

Ten minutes later, qualified as an expert in the mysterious art of HGN, the officer will opine that 6 of 6 clues – three in each eye – for lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and onsent of nystagmus prior to 45 degrees – means the person was likely impaired.

And on that testimony, people are convicted, at least here in North Carolina, of Driving While Impaired, a criminal offense.

All of the scientific literature in the world which shows that HGN is not a reliable indicator of impairment – much of it reviewed by Steven Rubenzer several years ago – does not stop the onslaught of bad HGN testimony.

There is absolutely no peer-reviewed scientific or medical literature that shows the linkage between supposed impairment and HGN. NHTSA has never produced a single peer-reviewed study to that effect.

North Carolina is a particularly bad place when it comes to this testimony. The legislature has attempted to lower the standards with respect to the admissibility of HGN.

Other states have been more circumspect. Here’s the Kansas Supreme Court in Wichita v. Molitor, declaring that:

One must show that any proffered evidence [HGN] that is ostensibly based upon scientific principles does, in fact, have some credible correlation to the matter that must be proved. For instance, consider the hypothetical scenario of an officer who testified that the officer had undergone extensive training in the operation of a Ouija Board? that when a Ouija Board is asked if the driver being tested is DUI, the Board’s arrow will point at “yes” or “no”? that random sampling has shown that the Ouija Board correctly identifies when a driver’s intoxication exceeds the legal limit 60% of the time? and that the Board’s arrow pointed at “yes” when asked if Molitor was DUI. Should *1283 a court allow the officer to base reasonable suspicion upon the Ouija Board test results? Of course not. And at this point in the state of Kansas, the HGN test has no more credibility than a Ouija Board or a Magic 8 Ball.

The fact is that HGN is unreliable. It is a ouija board. It is the magic 8 ball. It is used because it’s cheap and quick to use. But it doesn’t purport to identify what it says it identifies.

And the fact that an officer may have performed the test 100 or 1,000 and says it’s useful is simply confirmation bias.



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