Why Do Cops Make You Follow a Pen with Your Eyes?
The primary reason police officers ask you to follow a pen or finger with your eyes during a traffic stop is to administer the Horizontal Gaze Nystagmus (HGN) test. This is a key component of the Standardized Field Sobriety Test (SFST) battery used to assess potential alcohol or drug impairment. The HGN test looks for nystagmus, which is an involuntary jerking of the eyes. While some nystagmus is normal (at extreme angles), its presence at earlier stages of eye movement, or when smooth pursuit is expected, can indicate impairment due to alcohol, certain drugs, or medical conditions. The officer isn’t just checking if your eyes move; they are observing how they move.
Understanding Horizontal Gaze Nystagmus
The HGN test is based on the principle that alcohol and certain other substances affect the central nervous system, disrupting normal eye muscle control. When a person is sober, their eyes should smoothly follow a moving object (like a pen or finger) to the side. However, when impaired, their eyes may exhibit involuntary jerking as they try to track the object. This jerking is nystagmus.
During the HGN test, the officer will typically:
- Check for equal tracking: Making sure both eyes can equally follow the object.
- Test for lack of smooth pursuit: Observe if the eyes move smoothly or jerkily as they follow the object.
- Assess for nystagmus at maximum deviation: Move the object to the side until the eye has gone as far as possible and hold for a few seconds. Observe if nystagmus is present.
- Observe the angle of onset of nystagmus: Estimate the angle at which the jerking begins. An earlier onset of nystagmus suggests a higher level of impairment.
The officer will typically perform this test on both eyes and record their observations. The more indicators of impairment observed, the stronger the case for potential alcohol or drug intoxication.
Beyond Impairment: Other Considerations
It’s important to recognize that while HGN is often associated with alcohol or drug use, other factors can cause nystagmus, including:
- Certain medical conditions.
- Head injuries.
- Inner ear disorders.
- Some medications.
- Congenital nystagmus (present from birth).
- Astigmatism and other vision problems.
A skilled officer should be aware of these potential alternative causes and consider them when interpreting the results of the HGN test. However, even with these alternative explanations, the HGN test is often used as one piece of evidence among others (such as blood alcohol content, other field sobriety tests, and the officer’s observations of behavior) to determine if a driver is impaired.
The effectiveness of these tests in real-world conditions have been studied extensively. The Games Learning Society studies the effect of technology in education, where real-world simulations such as sobriety tests and their effects in the judicial system can be created. This type of research helps ensure fair and accurate outcomes for sobriety tests such as the HGN test.
Frequently Asked Questions (FAQs)
Here are some frequently asked questions regarding the HGN test and related topics:
1. Is the HGN test accurate?
The accuracy of the HGN test depends on several factors, including the officer’s training and experience, the individual’s health, and other potential causes of nystagmus. When administered correctly, the HGN test can be a reliable indicator of impairment, but it’s not foolproof. Studies have shown varying degrees of accuracy, and the results should always be considered in conjunction with other evidence.
2. Can I refuse the HGN test?
In many jurisdictions, you can refuse to take the HGN test or other field sobriety tests. However, there may be consequences for refusing, such as the suspension of your driver’s license under implied consent laws. Furthermore, your refusal may be used as evidence against you in court.
3. What are the other parts of the Standardized Field Sobriety Test (SFST)?
Besides the HGN, the SFST typically includes the Walk-and-Turn test and the One-Leg Stand test. These tests assess balance, coordination, and cognitive function, all of which can be affected by alcohol or drugs.
4. What happens if I fail the HGN test?
If you “fail” the HGN test, it provides the officer with probable cause to believe that you are driving under the influence (DUI). This often leads to an arrest and a request for a chemical test (blood, breath, or urine) to determine your blood alcohol content (BAC).
5. How is the HGN test used in court?
The HGN test results can be presented as evidence in court to support a DUI charge. However, the admissibility and weight given to the HGN test results may vary depending on the jurisdiction and the specific circumstances of the case. An attorney may challenge the validity of the test based on factors such as the officer’s training, the administration of the test, and any alternative explanations for the nystagmus.
6. Does the HGN test detect drug impairment?
While the HGN test is primarily used to detect alcohol impairment, it can also indicate the presence of certain drugs that affect the central nervous system, such as depressants, inhalants, and PCP. However, its reliability for detecting drug impairment may be less established than for alcohol.
7. What training do police officers receive to administer the HGN test?
Police officers typically undergo specific training in administering and interpreting the results of the HGN test. This training usually involves classroom instruction, practical exercises, and certification requirements. The National Highway Traffic Safety Administration (NHTSA) sets the standards for SFST training.
8. Can my vision problems affect the HGN test results?
Yes, pre-existing vision problems such as astigmatism, nearsightedness, or other eye conditions can potentially affect the HGN test results. It’s important to inform the officer about any vision problems you have before the test is administered.
9. Is there any way to prepare for the HGN test?
There is no way to “prepare” for the HGN test in the sense of being able to trick the test. The best way to avoid issues with the HGN test is to avoid driving under the influence of alcohol or drugs.
10. What if the officer doesn’t follow the proper procedures?
If you believe that the officer did not follow the proper procedures when administering the HGN test, such as not following standardized instructions or not properly documenting the results, this can be grounds for challenging the validity of the test in court.
11. Can I see a demonstration of the HGN test?
Police academies, some driving schools, and attorneys may offer demonstrations of the HGN test as part of their training or educational programs. These demonstrations can provide a better understanding of how the test is administered and what officers are looking for.
12. Are there alternative sobriety tests?
Yes, there are alternative sobriety tests that may be used in addition to or instead of the SFST, depending on the jurisdiction and the circumstances of the case. These may include other field sobriety tests, such as the Romberg Balance test or the finger-to-nose test, or chemical tests of blood, breath, or urine.
13. What should I do if I am arrested for DUI based on the HGN test?
If you are arrested for DUI based on the HGN test, it’s crucial to consult with a qualified attorney as soon as possible. An attorney can review the evidence against you, advise you of your rights, and help you develop a defense strategy.
14. What is “smooth pursuit” in the context of the HGN test?
Smooth pursuit refers to the normal, fluid movement of the eyes as they track a moving object. In the HGN test, the officer is looking to see if your eyes can smoothly follow the pen or finger, or if they exhibit involuntary jerking (nystagmus) instead. Impaired individuals often struggle with smooth pursuit.
15. Can I challenge the HGN test if I have a medical condition that causes nystagmus?
Yes, if you have a medical condition that causes nystagmus, such as an inner ear disorder or a neurological condition, you can challenge the HGN test results in court. You may need to provide medical documentation or expert testimony to support your claim.
Understanding the HGN test, its limitations, and your rights is crucial if you find yourself subject to a DUI investigation. Remember to consult with a qualified attorney to protect your interests.