Despite its history of use and the endorsement of the Department of Transportation's National Highway Traffic Safety Administration, the horizontal gaze nystagmus (HGN) field sobriety test is not fully understood. What is nystagmus? How does the presence of horizontal gaze nystagmus reflect alcohol impairment? How does the police officer test for HGN? What conclusions can reasonably be drawn from the presence of HGN?

In an effort to provide accurate information regarding the use of the HGN test in impaired driving enforcement and dispel the continuing controversy around HGN, the American Prosecutors Research Institute (APRI) is proud to provide criminal justice practitioners nationwide with Horizontal Gaze Nystagmus - The Science and the Law: A Resource Guide for Judges, Prosecutors and Law Enforcement. Among other things, this guide provides an overview of the science supporting the HGN test as a valid indicator of impairment, distinguishes between HGN and other forms of nystagmus, and provides the necessary tools to establish admissibility of the HGN test in court.

APRI is grateful to the Department of Transportation National Highway Traffic Safety Administration for its financial support which made this guide possible. In particular, we would like to thank Glenn Karr for his expert advice in recognizing the need for this publication in the criminal justice field.

APRI is committed to assisting criminal justice practitioners in their efforts to increase public safety in their communities. APRI hopes that this guide will promote increased training, use and acceptance of the HGN test as a valid and reliable tool in detecting, prosecuting and adjudicating impaired drivers.

Newman Flanagan
American Prosecutors Research Institute
Executive Director
National District Attorneys Association