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Introduction
The horizontal gaze nystagmus (HGN) test is the first of the three standardized field sobriety tests administered in a Michigan operating-while-intoxicated (OWI) investigation, and it is the most scientifically contested. Unlike the walk-and-turn and one-leg stand, which require no specialized knowledge to interpret, HGN involves an officer's subjective observation of involuntary jerking of the eyes that the officer attributes to alcohol-induced disturbance of the central nervous system. As Rubenzer and Stevenson observed in their peer-reviewed review, Horizontal Gaze Nystagmus: A Review of Vision Science and Application Issues, 55 Journal of Forensic Sciences 394 (2010), HGN's indications of intoxication are subtle, are not common knowledge, and have roots in laboratory science and clinical medicine—and for those reasons HGN has often been regarded as a scientific test requiring expert testimony before admission as evidence.
I have been qualified by Michigan courts as an expert witness on HGN on numerous occasions, beginning with my qualification in the Genesee County District Court in June 2011 and continuing through the present. In 2007, I represented the defendant in People v Wyrybkowski, Court of Appeals Case No. 283673, in which the Michigan Court of Appeals held that a defense expert witness must be permitted to testify under Daubert in a challenge to the HGN test. This page addresses the vision science underlying the test, the four NHTSA validation studies as they bear on HGN, the Rubenzer and Stevenson peer-reviewed critique, the Robustness Study commissioned by NHTSA in response to defense challenges, the categories of administrative error that I most frequently identify in Michigan cases, and the Michigan statutory and evidentiary framework that controls admissibility. The general framework of the standardized battery, the walk-and-turn, the one-leg stand, the validation studies, and the substantial-compliance requirement of MCL 257.62a are addressed on the dedicated Standardized Field Sobriety Tests (SFSTs) Expert Witness Services subpage.
What Is Nystagmus?
Nystagmus is an involuntary jerking of the eye, generally consisting of a slow drift in one direction followed by a rapid corrective saccade in the opposite direction. There are many forms of nystagmus, only some of which are associated with alcohol consumption. The canonical clinical reference, Dell'Osso and Daroff, Nystagmus and Saccadic Intrusions and Oscillations, in Tasman and Jaeger, eds., Duane's Clinical Ophthalmology, Vol. 2 (Lippencott, Williams & Wilkins, rev. ed. 2005), enumerates dozens of distinct nystagmus types. Page 14 of Session 8 of the 2023 NHTSA Participant Manual acknowledges that HGN is not the only kind of nystagmus, and groups other forms into three general categories: vestibular, neural, and pathological disorders and diseases.
The principal nystagmus categories relevant to OWI investigations are gaze-evoked or end-point nystagmus, optokinetic nystagmus, vestibular nystagmus, congenital or infantile nystagmus, and various drug- and disease-induced nystagmus. The 1981 Tharp, Burns, and Moskowitz study (Development and Field Test of Psychophysical Tests for DWI Arrest, Final Report, DOT-HS-805-864) documented at page 17 that approximately half of the 296 test subjects exhibited some nystagmus in at least one eye when their eyes were deviated maximally—before any alcohol was consumed. The peer-reviewed eye-movement literature documents the same phenomenon. Abel, Parker, Daroff, and Dell'Osso, End-Point Nystagmus, 17 Investigative Ophthalmology & Visual Science 539 (June 1978), studied twelve normal subjects and found that seven developed persistent end-point nystagmus, with one subject's nystagmus beginning at only 20 degrees of lateral deviation. The Abel study also documented earlier work by Blomberg, Godde-Jolly, and Uemura demonstrating that gaze-evoked nystagmus is common in healthy individuals at lateral gaze angles of 30 to 65 degrees, and that the distinction between physiological and pathological gaze nystagmus is, in the words of Uemura, "arbitrary, sometimes difficult and may be impossible."
From Alcohol Gaze Nystagmus to Horizontal Gaze Nystagmus
The 1977 Burns and Moskowitz study—Psychophysical Tests for DWI Arrest, Final Report, DOT-HS-802-424 (NHTSA 1977)—tested an early version of the eye test under the label "alcohol gaze nystagmus" (AGN). The 1981 follow-up study replaced AGN with HGN and refined the standardized administration and scoring procedure. The substitution was not merely linguistic. AGN had been described as an autonomic reaction specific to central nervous system depressants, primarily alcohol. HGN, as redefined for the standardized battery, describes any involuntary jerking of the eye observed under the prescribed administration conditions, regardless of cause. This expansion of the construct, which the 1981 study did not explicitly justify, has had significant consequences for the test's specificity in the field.
The earlier finding that recurs throughout the literature is the relationship between blood alcohol concentration and the angle of nystagmus onset. The 1981 study at Figure 2 reported a regression of angle of nystagmus onset on BAC, with the right-eye regression line described by Y = 58.01 + (-152.71)X and the left-eye regression line described by Y = 55.13 + (-138.10)X, where Y is the angle of onset in degrees and X is the BAC in percent. At a BAC of zero, the predicted angles of onset under that regression are approximately 55 to 58 degrees, well outside the 45-degree threshold used as a clue in the field test. The same study's Figure 3 documented variation in the angle of onset as a function of time of day, with subjects whose BAC was zero showing a meaningful drop in angle of onset between the 8 PM to midnight and midnight to 4 AM observation windows—an effect attributable to fatigue rather than alcohol.
The NHTSA Administration Protocol
NHTSA has codified a detailed administration protocol for HGN, set out at pages 23 through 34 of Session 8 of the 2023 NHTSA Participant Manual. The protocol identifies three clues that the officer is to look for, two in each eye, for a maximum of six clues across both eyes:
Lack of smooth pursuit (clue number one) is described in NHTSA Session 8, page 23, as the eyes' visible jerking or "bouncing" as they follow a smoothly moving stimulus. NHTSA acknowledges that this clue is not, strictly speaking, a form of nystagmus at all, but is included in the test as a "validated clue."
Distinct and sustained nystagmus at maximum deviation (clue number two), described in NHTSA Session 8, pages 23 and 33, requires the officer to move the stimulus as far to the side as the eye will go, hold the stimulus steady at that position for a minimum of four seconds, and observe whether nystagmus is both distinct and sustained.
Onset of nystagmus prior to 45 degrees (clue number three), described in NHTSA Session 8, page 23, requires the officer to move the stimulus from center toward the side at a speed that takes approximately four seconds or more to travel from center to a point estimated as 45 degrees, and to identify the angle at which nystagmus first becomes evident. NHTSA's most recent training instructs the officer to estimate 45 degrees by moving the stimulus to the side a distance equal to the distance from the stimulus to the subject. A secondary guideline, which Rubenzer and Stevenson observed was the only one before 2006, is to align the stimulus with the tip of the shoulder—a method that they noted will usually result in gross underestimation of 45 degrees.
The full administrative procedure, as set out at pages 24 and 25 of Session 8 of the 2023 Participant Manual, requires ten steps in order: check for eyeglasses; deliver verbal instructions; position the stimulus 12 to 15 inches from the subject's face and slightly above eye level; check for equal pupil size and resting nystagmus; check for equal tracking; check for lack of smooth pursuit; check for distinct and sustained nystagmus at maximum deviation; check for onset of nystagmus prior to 45 degrees; total the clues; and check for vertical gaze nystagmus. NHTSA Session 8, page 26, emphasizes in bold that there should be a clear, distinguishable break between the check for equal tracking and the check for lack of smooth pursuit. NHTSA Session 8, page 30, requires the officer to begin each check with the subject's left eye, complete that check on the left eye, then check the right eye for the same clue, and then return to the left eye to begin the next clue. NHTSA Session 8, page 32, requires the stimulus to be moved at a speed that takes approximately two seconds to bring the eye from center to side during the smooth pursuit check, with at least two complete passes in front of the eyes.
NHTSA Session 8, page 29, instructs that if four or more clues are observed across the two eyes, it is likely that the subject's BAC is at or above 0.08, and that the test will classify approximately 88 percent of subjects accurately. As discussed below and on the SFST subpage, this 88 percent figure is drawn from the San Diego Validation Study—Stuster and Burns, Validation of the Standardized Field Sobriety Test Battery at BACs Below 0.10 Percent, Final Report, DOT-HS-808-839 (NHTSA, August 1998)—and replaces a 77 percent figure derived from the 1981 study without adequate explanation by NHTSA.
The Vision Science Critique: Rubenzer and Stevenson
The most thorough peer-reviewed critique of HGN as administered in the field is Rubenzer and Stevenson, Horizontal Gaze Nystagmus: A Review of Vision Science and Application Issues, 55 Journal of Forensic Sciences 394 (2010). Steven J. Rubenzer is a forensic psychologist, and Scott B. Stevenson is a vision scientist. Their review concluded that HGN is limited by large variability in the underlying normative behavior of the eye, by methods and testing environments that are often poorly controlled, and by a lack of rigorous validation in laboratory settings.
The Rubenzer and Stevenson critique identifies five categories of limitation. First, there is minimal evidence that HGN is related to driving or behavioral impairment. Second, there are no true double-blind studies that would provide an unbiased estimate of HGN's relation to BAC. Third, the interrater reliability figures reported for HGN, ranging from 0.59 to 0.71 across the principal validation studies, are below the 0.80 standard advocated by Heilbrun and far below the 0.90 minimum recommended by Nunnally and Bernstein for tests on which arrest decisions and evidence of impairment in legal proceedings are based. Fourth, HGN is susceptible to medical conditions and certain medications. Fifth, confounding factors—anxiety, fatigue, circadian rhythms—are commonly present at DWI stops.
The same article cites Dell'Osso and Daroff for the proposition that nystagmus as an indicator of alcohol intoxication is fraught with extraordinary pitfalls: many normal individuals have physiologic end-point nystagmus; small doses of tranquilizers that would not interfere with driving ability can also produce nystagmus; nystagmus may be congenital or consequent to structural neurologic disease; and a neuro-ophthalmologist or sophisticated oculographer is often required to determine whether nystagmus is pathologic. Rubenzer and Stevenson observed that judgments of this kind are difficult for experts to make under the best conditions and impossible to make accurately under roadside conditions, and they concluded that it is unreasonable to have cursorily trained law officers using the test, no matter how intelligent, perceptive, and well-meaning they might be.
Rubenzer and Stevenson also addressed a fundamental measurement-science problem with HGN. In any analytical instrument used in forensic science, the instrument itself is calibrated against accepted standards, and the variability in measurement attributable to instrument noise is known. In HGN testing, the "instrument" is the arresting officer, who makes a subjective assessment of whether nystagmus is present or "distinct." Presumably, this varies with the number and size of saccades, but no peer-reviewed study has examined the HGN administrator's judgments of saccade frequency and amplitude against an objective eye-tracker recording. The instrument, in short, is uncalibrated.
The Robustness Study (2007)
In 2003, in response to defense arguments that HGN should be inadmissible when an officer's administration of the test varied from the standardized procedure, Marcelline Burns undertook a study at the Southern California Research Institute to demonstrate that the test was insensitive to procedural variation. The study, published as NHTSA's The Robustness of the Horizontal Gaze Nystagmus Test, was delayed for four years without explanation and was released quietly in 2007 with little public attention. Burns concluded that the data demonstrated the validity of the HGN test with both standard and varied testing procedures, and that the variations did not alter the occurrence of, or the observation of, HGN. Close examination of the Robustness Study's own data does not support that conclusion.
The Robustness Study examined three procedural variables in stimulus administration: stimulus speed (the standard two-second center-to-side passage compared with a one-second passage), stimulus elevation (the standard two inches above eye level compared with eye level and four inches above eye level), and stimulus distance from the face (the standard 12 to 15 inches compared with 10 inches and 20 inches). The data are compiled at Tables 10, 13, and 15 of the report.
Table 10 of the Robustness Study, at page 14, reports that 77 percent of test subjects below 0.08 BAC nevertheless demonstrated four or more HGN clues when the test was completed properly by highly trained DRE officers, and that the false-arrest rate among that population dropped to 50 percent only when officers performed the test recklessly fast. Table 13, at page 18, reports that the false-positive rate increased to 92 percent when the stimulus was held at four inches above eye level, with 22 of 24 subjects below 0.08 scoring four or more clues. Table 15, at page 21, reports that the false-positive rate increased to 93 percent when the stimulus was held at 10 inches from the subject's face, with 25 of 27 subjects below 0.08 scoring four or more clues. The same study attributed over 40 percent of the variability in HGN observations to differences between participants—an intraclass correlation that confirms what the Abel et al. (1978) end-point nystagmus data had suggested, namely that a substantial fraction of the human population displays nystagmus under HGN test conditions in the absence of alcohol.
These figures, drawn from NHTSA's own data, are difficult to reconcile with the conclusion that the HGN test is robust to administrative variation. They are also impossible to reconcile with NHTSA's continued use of an 88 percent classification accuracy figure in officer training.
Other Nystagmus Conditions Relevant to OWI Investigation
Several other forms of nystagmus, all addressed in the NHTSA training materials and in the peer-reviewed literature, can produce false positives on the HGN test.
Optokinetic nystagmus. NHTSA Session 8, page 16, describes optokinetic nystagmus as nystagmus that occurs when the eyes fixate on an object that suddenly moves out of sight, or when the eyes watch sharply contrasting moving images. Examples include strobe lights, rotating lights, and rapidly moving traffic in close proximity. Officers who fail to turn off their flashing overhead lights before conducting the HGN test, or who position the subject facing toward the patrol vehicle or toward passing traffic, induce optokinetic nystagmus that is indistinguishable from alcohol-induced nystagmus to a roadside observer. The instructor manual at Session 8, page 17, expressly directs officers to face the driver away from potential distractions in anticipation of this well-known issue.
Resting nystagmus. NHTSA Session 8, page 19, describes resting nystagmus as a jerking of the eyes as they look straight ahead, and states that its presence usually indicates a medical condition or high doses of a dissociative anesthetic drug. The pre-administration check for resting nystagmus required by NHTSA Session 8, page 21, is intended to identify subjects in whom the HGN test should not be conducted. Officers frequently omit this check or conduct it perfunctorily.
Fatigue nystagmus. NHTSA Session 8, page 34, asserts without supporting evidence that fatigue nystagmus is the result of the tiring of the eye muscles when the eyes are held at maximum deviation for at least 30 seconds, and that four seconds will not cause fatigue nystagmus. The peer-reviewed literature does not support that bright-line conclusion. Abel et al. (1978) documented sustained end-point nystagmus in healthy subjects with no or short latency intervals, and one subject in that study showed nystagmus at only 20 degrees of deviation. Schmidt and Kommerell (1976), the only quantitative oculographic investigation of horizontal gaze-evoked nystagmus in normals, found end-position fatigue nystagmus in one of six subjects after a latency of 90 seconds, and Barany (1906) reported that approximately 50 percent of normal subjects developed nystagmus when gaze was maximally deviated for longer than 30 seconds.
Vestibular and pathological nystagmus. Rubenzer and Stevenson (2010) emphasized that some medical conditions affecting the cerebellum or the neural integrator may disrupt smooth pursuit and cause gaze nystagmus that is indistinguishable from alcohol-induced nystagmus. Conditions affecting the neural integrator produce gaze nystagmus with the same waveform that is observed when alcohol is the cause: a decelerating drift from the original position of gaze followed by a saccade back to that position. There is, in their words, "nothing for a police officer to discriminate, as the expected waveforms are identical."
Vertical gaze nystagmus. NHTSA Session 8, page 19, asserts that the drugs that cause vertical gaze nystagmus (VGN) are the same ones that cause HGN. VGN has never been validated as a clue in any of the four NHTSA validation studies, and officers are frequently confused about its meaning, sometimes characterizing it as evidence of drug impairment in the absence of alcohol. The Michigan Court of Appeals addressed officer confusion about VGN in People v Bouwman, Unpublished Per Curiam Opinion, Court of Appeals Docket No. 307325 (May 29, 2014), in which an officer testified that the presence of irregularities in the vertical movement of a test subject's eyes indicated that the subject was under the intoxicating influence of drugs, not alcohol—a proposition that the prosecutor then used as evidence that the defendant had drugged the complainant.
Michigan Statutory and Evidentiary Framework
Michigan law treats HGN distinctly within the broader framework that governs SFST evidence. The general framework—MCL 257.62a's substantial-compliance requirement and MCL 257.625s's expert-qualification provision—is addressed on the SFST subpage. Three additional propositions are specific to HGN.
First, MCL 257.625s expressly identifies the horizontal gaze nystagmus test as one of the standardized tests in the administration of which an expert may be qualified by knowledge, skill, experience, training, or education to testify subject to a showing of a proper foundation of qualifications. The statute thus contemplates expert testimony, both prosecution and defense, on HGN.
Second, the Michigan Court of Appeals has held that HGN evidence is admissible only to establish the presence of alcohol, not to establish a specific BAC. People v Berger, 217 Mich App 213 (1996). HGN is therefore not a substitute for chemical testing under Michigan law and cannot, for example, be offered to corroborate or impeach a particular Datamaster or Intoxilyzer 9000 result.
Third, the Michigan Court of Appeals held in 2007, in a case I argued on behalf of the defendant, that a defense expert witness must be permitted to testify under Daubert in a challenge to the HGN test. People v Wyrybkowski, Court of Appeals Case No. 283673 (2007). This decision established that the trial court's gatekeeping function under MRE 702 and Daubert v Merrell Dow Pharmaceuticals, Inc, 509 US 579 (1993) applies symmetrically to prosecution and defense expert testimony on HGN.
The Michigan Court of Appeals has also observed in unpublished decisions that HGN administrative failures can warrant evidentiary scrutiny. In People v Farnsworth, Unpublished Per Curiam Opinion, Court of Appeals Docket No. 371509 (May 23, 2025), the Court noted that the officer testified that he was trained to repeat the HGN test (tracking the stimulus two times for each eye) but did not do so in the case at issue, and that he sometimes held the stimulus for four seconds as he was supposed to do and sometimes did not. The Court characterized this as an admission that the officer did not perform all aspects of the test correctly. The general aura-of-scientific-infallibility concern that motivates careful judicial scrutiny of forensic evidence has been addressed in People v Haywood, 209 Mich App 217 (1995), and at the United States Supreme Court level by Justice Blackmun's dissent in Barefoot v Estelle, 463 US 880, 926 (1983) (Blackmun, J., dissenting), where the Justice observed that an aura of scientific infallibility may shroud unreliable scientific evidence and lead the jury to accept it without critical scrutiny.
Common HGN Administrative Failures Identified in Michigan Cases
The Robustness Study data, taken together with the Rubenzer and Stevenson critique, identify the categories of administrative error that most often compromise the validity of an HGN test in the field. I encounter the following failures with predictable regularity in the Michigan cases I review.
Failure to turn off overhead emergency lights. Officers who conduct the HGN test with the patrol vehicle's red and blue strobes operating, or who position the subject facing the patrol vehicle, induce optokinetic nystagmus that contaminates the result.
Improper stimulus distance. NHTSA Session 8, page 24, requires the stimulus to be held 12 to 15 inches from the subject's face. The Robustness Study found at Table 15 that holding the stimulus at 10 inches produced a false-positive rate of 93 percent for subjects below 0.08 BAC. Officers who hold the stimulus too close (often visible on body-worn camera as the officer's hand crowding the subject's face) systematically over-detect nystagmus.
Improper stimulus elevation. NHTSA training requires the stimulus to be held slightly above eye level, generally specified as approximately two inches above the bridge of the nose. The Robustness Study found at Table 13 that elevating the stimulus to four inches above eye level produced a false-positive rate of 92 percent for subjects below 0.08.
Improper stimulus speed during smooth-pursuit phase. NHTSA Session 8, page 32, requires the stimulus to move at a speed that takes approximately two seconds to bring the eye from center to side, with at least two complete passes. Officers who move the stimulus too quickly induce false saccadic intrusions that can be misread as lack of smooth pursuit.
Improper hold time at maximum deviation. NHTSA Session 8, page 33, requires the stimulus to be held at maximum deviation for a minimum of four seconds. Officers who hold for less than four seconds cannot reliably distinguish between distinct and sustained nystagmus at maximum deviation (which they are looking for) and end-point nystagmus that begins and dissipates over the course of seconds (which is normal).
Improper estimation of 45 degrees. The 45-degree threshold is critical to clue number three, but officers are estimating the angle by visual approximation under non-ideal conditions. The 1981 study's regression of angle of nystagmus onset on BAC predicts an angle of onset of approximately 55 to 58 degrees in a sober subject; an officer who underestimates the 45-degree threshold (a common error when the shoulder-tip method is used) will systematically score false positives on this clue.
Failure to perform pre-test medical checks. The check for equal pupil size, resting nystagmus, and equal tracking required by NHTSA Session 8, page 21, is the only screening designed to identify subjects in whom HGN administration is contraindicated. NHTSA Session 8, page 26, expressly requires a clear, distinguishable break between the equal-tracking check and the smooth-pursuit check. Officers who combine these checks, or who perform them perfunctorily, fail the threshold gate-keeping function that the protocol assigns them.
Improper sequencing. NHTSA Session 8, page 30, requires a specific sequence: begin with the subject's left eye, complete the check on the left eye, then check the right eye for the same clue, and then move to the next clue starting again with the left eye. Officers who score both clues in one eye before moving to the other, or who score multiple clues simultaneously, are administering an unvalidated variant of the test. Importantly, if an officer does not detect lack of smooth pursuit, that officer should not detect distinct and sustained nystagmus at maximum deviation, because the latter cannot occur in the absence of the former.
Conflation of distinct clues. Officers occasionally describe their observations using compound formulations such as "early onset nystagmus at maximum deviation"—a phrase that is scientifically incoherent because the two clues describe different signs observed at different points in the examination, the former at approximately 45 degrees and the latter at the extreme periphery. This kind of conflation invalidates the reliability of the observation.
My Training and Experience with HGN
I completed the NHTSA/IACP Standardized Field Sobriety Testing Practitioner Certification Course in April 2005. In 2008, I completed advanced training in Horizontal Gaze Nystagmus (HGN): Vision Science Perspectives, a specialized course focused on the eye-movement physiology by Rubenzer and Stevenson. I have served as a trainer at NHTSA/IACP Live Alcohol Workshops in 2007, 2009, 2012, and 2017, and at NHTSA/IACP Advanced Roadside Impaired Driving Enforcement (ARIDE) training in 2017. The Live Alcohol Workshop and ARIDE settings provided me with direct, repeated experience administering the HGN test on dosed volunteer subjects whose actual BACs were known.
I have studied and applied the underlying primary literature, including the 1977 Burns and Moskowitz study, the 1981 Tharp, Burns, and Moskowitz study, the Colorado, Florida, and San Diego validation studies, the Robustness Study, and the Rubenzer and Stevenson Journal of Forensic Sciences review (2010). I read these sources rather than relying on summary slides or prosecutor-published synopses.
From 2021 through 2024, I served as an Adjunct Professor of Forensic Science at Madonna University, where I taught FOR 4650 Ethics & Expert Testimony and FOR/CJ 5230 Criminal Law and the Rules of Evidence. The course content included substantial instruction on the Daubert framework as applied to forensic evidence of the kind at issue in HGN proceedings.
Courtroom Qualification on HGN
Michigan courts have qualified me as an expert witness on HGN on numerous occasions. The earliest of these qualifications occurred on June 23, 2011, in the Genesee County District Court. On November 14, 2012, I provided evidentiary hearing testimony before the Honorable Susan H. Grant in the 77th District Court for Mecosta County regarding the technical requirements of the HGN test as part of broader testimony on the SFST battery. On March 15, 2013, I was qualified and testified as an expert on the SFST battery, including HGN, before the Honorable Debra Nance in the 46th District Court for Oakland County, with that testimony recorded by major news stations in the Metro Detroit area.
In 2007, as already noted, I represented the defendant in People v Wyrybkowski, Court of Appeals Case No. 283673, in which the Michigan Court of Appeals held that a defense expert witness must be permitted to testify under Daubert in a challenge to the HGN test. The Wyrybkowski decision is a published precedent on the symmetrical application of MRE 702 to prosecution and defense expert testimony on field sobriety testing.
I have lectured on HGN issues in numerous continuing legal education programs, including Cross Examination on Flawed Field Sobriety Tests for the Michigan Association of OWI Attorneys (MIAOWIA) in 2024 and Introduction to Field Sobriety Testing and Statistical Flaws in the SFST Battery at the Criminal Defense Attorneys of Michigan (CDAM) Summer Session in 2012. I authored Witness Preparation and Examination for DUI Proceedings, published by West in 2012. In 2015, I provided testimony before the Michigan Senate Judiciary Committee regarding standardized field sobriety testing.
Scope of Engagement
A typical HGN expert engagement begins with my review of the police narrative report, the in-car and body-worn camera video, the officer's HGN data sheet (or its absence, which is itself a finding), the officer's training records, any contemporaneous medical history bearing on possible alternative causes of nystagmus, and any prescription-medication information. The video record is particularly important because the HGN test is fundamentally an exercise in officer perception, and reliable evaluation of the officer's perception requires reliable visual evidence of the test as administered.
I then prepare a written expert report that identifies, on a step-by-step basis, every departure from the NHTSA-prescribed protocol, every clue that was scored without an adequate physical basis on the video, every confounding factor (optokinetic, vestibular, fatigue, or medical) that the officer failed to control for, and every conflation or misstatement of the HGN clues in the officer's narrative. The report relates each identified failure to the underlying scientific literature—most often the 1981 study, the Robustness Study, and Rubenzer and Stevenson (2010)—and explains, in language accessible to the trier of fact, why each failure undermines the inference of impairment that the prosecution will draw from the test.
Retention
I accept HGN expert witness engagements from defense attorneys throughout Michigan and, on a case-by-case basis, in neighboring jurisdictions. Inquiries may be directed to Maze Legal PLC, 37211 Goddard Road, Romulus, Michigan 48174, or by telephone at (734) 941-8800.
