Visual Vestibular Conflict Mitigation in Virtual Reality Using Galvanic Vestibular Stimulation.

BACKGROUND: Virtual reality (VR) is an effective technique to reduce cost and increase fidelity in training programs. In VR, visual and vestibular cues are often in conflict, which may result in simulator-induced motion sickness. The purpose of this study is to investigate the integration of Galvanic Vestibular Stimulation (GVS) with a VR flight training simulator by assessing flight performance, secondary task performance, simulator sickness and presence.METHODS: There were 20 participants who performed 2 separate VR flight simulation sessions, with and without GVS (control). Flight performance, secondary task performance, and electrogastrogram were measured during VR flight simulation. The standardized simulator sickness and presence questionnaires were administered.RESULTS: Electrogastrogram measures such as dominant power instability coefficient (DPIC) and percentages of bradygastric waves (%B) were lower in the GVS session than the control session in the flight simulation (DPIC: 0.44 vs. 0.54; %B: 21.2% vs. 30.5%) and postflight (DPIC: 0.38 vs. 0.53; %B: 22.8% vs. 31.4%) periods. Flight performance (#hit-gates) was improved in the GVS session compared to the control (GVS: 17, Control: 15.5). Secondary task performance (%hits) was improved with GVS for the Easy task (GVS: 55.5%, Control: 43.1%).DISCUSSION: This study demonstrates the potential of synchronizing GVS with visual stimuli in VR flight training to reduce visual-vestibular sensory conflict to improve fidelity and performance. These results provide initial evidence, but continued research is warranted to further understand the benefits and applications of GVS in VR simulator training.Pradhan GN, Galvan-Garza RC, Perez AM, Stepanek J, Cevette MJ. Visual vestibular conflict mitigation in virtual reality using galvanic vestibular stimulation. Aerosp Med Hum Perform. 2022; 93(5):406-414.

Generating Flight Illusions Using Galvanic Vestibular Stimulation in Virtual Reality Flight Simulations.

Background: Vestibular flight illusions remain a significant source of concern for aviation training. Most fixed-based simulation training environments, including new virtual reality (VR) technology, lack the ability to recreate vestibular flight illusions as vestibular cues cannot be provided without stimulating the vestibular end organs. Galvanic vestibular stimulation (GVS) has long been used to create vestibular perception. The purpose of this study is to evaluate the ability of GVS to simulate common flight illusions by intentionally providing mismatched GVS during flight simulation scenarios in VR. Methods: Nineteen participants performed two flight simulation tasks-take off and sustained turn-during two separate VR flight simulation sessions, with and without GVS (control). In the GVS session, specific multi-axis GVS stimulation (i.e., electric currents) was provided to induce approximate somatogravic and Coriolis illusions during the take-off and sustained turn tasks, respectively. The participants used the joystick to self-report their subjective motion perception. The angular joystick movement along the roll, yaw, and pitch axes was used to measure cumulative angular distance and peak angular velocity as continuous variables of motion perception across corresponding axes. Presence and Simulator Sickness Questionnaires were administered at the end of each session. Results: The magnitude and variability of perceived somatogravic illusion during take-off task in the form of cumulative angular distance (p < 0.001) and peak velocity (p < 0.001) along the pitch-up axis among participants were significantly larger in the GVS session than in the NO GVS session. Similarly, during the sustained turn task, perceived Coriolis illusion in the form of cumulative angular distances (roll: p = 0.005, yaw: p = 0.015, pitch: p = 0.007) and peak velocities (roll: p = 0.003, yaw: p = 0.01, pitch: p = 0.007) across all three axes were significantly larger in the GVS session than in the NO GVS session. Subjective nausea was low overall, but significantly higher in the GVS session than in the NO GVS session (p = 0.026). Discussion: Our findings demonstrated that intentionally mismatched GVS can significantly affect motion perception and create flight illusion perceptions during fixed-based VR flight simulation. This has the potential to enhance future training paradigms, providing pilots the ability to safely experience, identify, and learn to appropriately respond to flight illusions during ground training.

Oculometric Feature Changes During Acute Hypoxia in a Simulated High-Altitude Airdrop Scenario.

BACKGROUND: Severe acute hypoxia results in a rapid deterioration of cognitive functioning and thus poses a risk for human operations in high altitude environments. This study aimed at investigating the effects of oxygen system failure during a high-altitude high-opening (HAHO) parachute jump scenario from 30,000 ft (9144 m) on human physiology and cognitive performance using a noncontact eye-tracking task.METHODS: Nine healthy male volunteers (ages 27-48) were recruited from the Norwegian Special Operations Commandos. Eye-tracking data were collected to derive information on cognitive performance in the context of rapid dynamic changes in pressure altitude while performing a modified King-Devick test. The baseline data was collected at 8000 ft (2438 m) while breathing 100% oxygen during decompression. For every test, the corresponding arterial blood gas analysis was performed.RESULTS: The study subjects endured severe hypoxia, which resulted in significant prolongations of fixation time (range: 284.1-245.6 ms) until 23,397 ft (131 m) and fixation size (range: 34.6-32.4 mm) until 25,389 ft (7739 m) as compared to the baseline (217.6 ± 17.8 ms and 27.2 ± 4.5 mm, respectively). The increase in the saccadic movement and decrease in the saccadic velocity was observed until 28,998 ft and 27,360 ft (8839 and 8339 m), respectively.DISCUSSION: This is the first study to investigate cognitive performance from measured oculometric variables during severe hypobaric hypoxia in a simulated high-altitude airdrop mission scenario. The measurement of altered oculometric variables under hypoxic conditions represents a potential avenue to study altered cognitive performance using noncontact sensors that can derive information and serve to provide the individual with a warning from impending incapacitation.Pradhan GN, Ottestad W, Meland A, Kåsin JI, Høiseth LØ, Cevette MJ, Stepanek J. Oculometric feature changes during acute hypoxia in a simulated high-altitude airdrop scenario. Aerosp Med Hum Perform. 2021; 92(12):928-936.

Supplemental CO2 improves oxygen saturation, oxygen tension, and cerebral oxygenation in acutely hypoxic healthy subjects.

Oxygen is viewed in medicine as the sole determinant of tissue oxygenation, though carbon dioxide homeostasis is equally important and clinically often ignored. The aims of this study were as follows: (a) to examine the effects of different acute hypoxic conditions on partial pressure of arterial oxygen ( PaO2 ), arterial oxygen saturation of hemoglobin ( SaO2 ), and regional cerebral saturation of hemoglobin (rSO2 ); and (b) to evaluate supplemental CO2 as a tool to improve oxygenation in acutely hypoxic individuals. We hypothesized that exposure to gas mixtures with added CO2 would improve oxygenation in hypoxic human subjects. Twenty healthy subjects were exposed to 5-min intervals of two gas mixtures: hypoxic gas mixture containing 8% oxygen, and a CO2 -enriched mixture containing 8% oxygen plus either 3% or 5% CO2 . Ten subjects received the 3% CO2 -enriched mixture, and the remaining 10 subjects received the 5% CO2 -enriched mixture. The order of exposure was randomized. Blood gases, pulse oximetry, end-tidal CO2 , and cerebral oximetry were measured. Compared to the purely hypoxic gas group, PaO2 was increased in the 3% and 5% CO2 -enriched groups by 14.9 and 9.5 mmHg, respectively. Compared to pure hypoxia, SaO2 was increased in the 3% and 5% CO2 -enriched groups by 16.8% and 12.9%, respectively. Both CO2 -enriched gas groups had significantly higher end-exposure rSO2 and recovered to baseline rSO2 within 1 min, compared to the pure hypoxic gas group, which returned to baseline in 5 min. These results suggest that in acutely hypoxic subjects, CO2 supplementation improves blood oxygen saturation and oxygen tension as well as cerebral oxygenation measures.

Discovering Oculometric Patterns to Detect Cognitive Performance Changes in Healthy Youth Football Athletes.

In this paper, we focus on the application of oculometric patterns extracted from raw eye movements during a mental workload task to assess changes in cognitive performance in healthy youth athletes over the course of a typical sport season. Oculometric features pertaining to fixations and saccades were measured on 116 athletes in pre- and post-season testing. Participants were between 7 and 14 years of age at pre-season testing. Due to varied developmental rates, there were large interindividual performance differences during a mental workload task consisting of reading numbers. Based on different reading speeds, we classified three profiles (slow, moderate, and fast) and established their corresponding baselines for oculometric data. Within each profile, we describe changes in oculomotor function based on changes in cognitive performance during the season. To visualize these changes in multidimensional oculometric data, we also present a multidimensional visualization tool named DiViTo (diagnostic visualization tool). These experimental, computational informatics and visualization methodologies may serve to utilize oculometric information to detect changes in cognitive performance due to mild or severe cognitive impairment such as concussion/mild traumatic brain injury, as well as possibly other disorders such as attention deficit hyperactivity disorders, learning/reading disabilities, impairment of alertness, and neurocognitive function.

Correlating Multi-dimensional Oculometrics with Cognitive Performance in Healthy Youth Athletes.

There is a need for a practical objective measure to detect mild changes in cognitive performance as early signs of concussion in youth or other special populations. In this paper, we propose a novel correlation model that establishes the relationship between oculometrics extracted from raw eye movements during a mental workload task and cognitive performance. We assessed differences in cognitive performance in terms of age for youth athletes based on oculometrics pertaining to fixations and saccades. In this cross-sectional study, oculometrics were measured on 440 healthy youth athletes aged 7 to 15 years. Oculometrics pertaining to fixations (fixation time, fixation size, and surface area of fixation) and saccades (total saccadic amplitude, average saccadic amplitude, and saccadic velocity) were measured and compiled into a multivariate oculometric database by age. We discovered that the combined power of fixations and saccades provided the strongest correlation with cognitive performance-a finding that is evident across all ages as well as all levels of mental workload difficulty. Specifically, the combined observations of fixation time, saccadic velocities, and saccadic amplitudes provided us an understanding of cognitive performance during different levels of mental workload difficulty across all age groups. This study is the first step towards establishing normative, multi-dimensional oculometrics for fixations and saccades in young athletes (7 to 15 years) who are at risk for concussion in sports and recreational activities.

Labyrinthine concussion following gunshot injury: A case report.

OBJECTIVE: Labyrinthine concussion due to a postauricular gunshot wound has not been well reported. DESIGN: Retrospective chart review. STUDY SAMPLE: We describe an otherwise healthy 22-year-old male who received a gunshot wound to the left mastoid and subsequently reported hearing loss and rotational vertigo. RESULTS: Audiometric testing demonstrated significant inverted scoop shaped sensorineural hearing loss. Vestibular diagnostic testing indicated a significant uncompensated left peripheral vestibulopathy. Imaging demonstrated no structural changes to the middle ear or labyrinth, suggesting that the auditory and vestibular losses noted on diagnostic examination were likely due to labyrinthine concussion. CONCLUSIONS: Labyrinthine concussion may lead to reduced vestibular reflex pathway following gunshot wounds to the temporal bone. Clinical presentation is likely to vary significantly among cases.

Acute hypoxic hypoxia and isocapnic hypoxia effects on oculometric features.

INTRODUCTION: Visual performance impairment after hypoxia is well recognized in military and civilian aviation. The aims of this study were: 1) to assess oculometric features such as blink metrics, pupillary dynamics, fixations, and saccades as cognitive indicators of early signs of hypoxia; and 2) to analyze the impact of different hypoxic conditions ["hypoxic hypoxia" (HH) and "isocapnic hypoxia" (IH)] on specified oculometrics during mental workloads. METHODS: Oculometric data were collected on 25 subjects under 3 conditions: normoxia, HH (8% O2 + balance N2), and IH (7% O2 + 5% CO2 + balance N2). The mental workload task consisted of reading aloud linear arrays of numbers after exposure to gas mixtures. RESULTS: Blink rates were significantly increased under hypoxic conditions (by +100.7% in HH and by +92.8% in IH compared to normoxia). A faster recovery of blink rate was observed in transitioning from IH (23.6% vs. 76.3%) to normoxia. The percentage change in pupil size fluctuation was increased under HH more than under IH (29% vs. 4.4%). Under HH average fixation time and target area size were significantly higher than under IH. Total saccadic times under hypoxic conditions were significantly increased compared with normoxia. CONCLUSIONS: These results suggest that oculometric changes are indicators of hypoxia, which can be monitored using compact, portable, noninvasive eye-tracking devices in a cockpit analogous environment to detect hypoxia-induced physiological changes in aircrew. Comparative results between HH and IH support the potential role of carbon dioxide in augmenting cerebral perfusion and hence improved tissue oxygen delivery.

Electrogastrographic and autonomic responses during oculovestibular recoupling in flight simulation.

INTRODUCTION: Simulator sickness causes vestibulo-autonomic responses that increase sympathetic activity and decrease parasympathetic activity. The purpose of the study was to quantify these responses through electrogastrography and cardiac interbeat intervals during flight simulation. METHODS: There were 29 subjects that were randomly assigned to 2 parallel arms: (1) oculovestibular recoupling, where galvanic vestibular stimulation was synchronous with the visual field; and (2) control. Electrogastrography and interbeat interval data were collected during baseline, simulation, and post-simulation periods. A simulator sickness questionnaire was administered. RESULTS: Statistically significant differences were observed in percentage of recording time with the dominant frequency of electrogastrography in normogastric and bradygastric domains between the oculovestibular recoupling and control groups. Normogastria was dominant during simulation in the oculovestibular recoupling group. In the control group, the percentage of recording time with the dominant frequency decreased by 22% in normogastria and increased by 20% in bradygastria. The percentage change of the dominant power instability coefficient from baseline to simulation was 26% in the oculovestibular recoupling group vs. 108% in the control group. The power of high-frequency components for interbeat intervals did not change significantly in the oculovestibular recoupling group and was decreased during simulation in the control group. DISCUSSION: Electrogastrography and interbeat intervals are sensitive indices of autonomic changes in subjects undergoing flight simulation. These data demonstrate the potential of oculovestibular recoupling to stabilize gastric activity and cardiac autonomic changes altered during simulator and motion sickness.

Early detection of hypoxia-lnduced cognitive impairment using the King-Devick test.

INTRODUCTION: Hypoxic incapacitation continues to be a significant threat to safety and operations at high altitude. Noninvasive neurocognitive performance testing is desirable to identify presymptomatic cognitive impairment, affording operators at altitude a tool to quantify their performance and safety. METHODS: There were 25 subjects enrolled in this study. Cognitive performance was assessed by using the King-Devick (K-D) test. The performance of the subjects on the K-D test was measured in normoxia followed by hypoxia (8% 02 equivalent to 7101 m) and then again in normoxia. RESULTS: K-D test completion time in hypoxia for 3 min was significantly longer than the Baseline Test (54.5 +/- 12.4 s hypoxic vs. 46.3 +/- 10.4 s baseline). Upon returning to normoxia the completion time was significantly shorter than in hypoxia (47.6 +/- 10.6 s post test vs. 54.5 +/- 12.4 s hypoxic). There was no statistically significant difference between baseline test and post test times, indicating that all subjects returned to their normoxic baseline levels. SpO2 decreased from 98 +/- 0.9% to 80 +/- 7.8% after 3 min on hypoxic gas. During the hypoxic K-D test, SpO2 decreased further to 75.8 +/- 8.3%. CONCLUSIONS: In this study the K-D test has been shown to be an effective neurocognitive test to detect hypoxic impairment at early presymptomatic stages. The K-D test may also be used to afford a reassessment of traditional measures used to determine hypoxic reserve time.

Pure-tone hearing asymmetry: a logistic approach modeling age, sex, and noise exposure history.

BACKGROUND: Asymmetric hearing loss (AHL) can be an early sign of vestibular schwannoma (VS). However, recognizing VS-induced AHL is challenging. There is no universally accepted definition of a "medically significant pure-tone hearing asymmetry," in part because AHL is a common feature of medically benign forms of hearing loss (e.g., age- or firearm-related hearing loss). In most cases, the determination that an observed AHL does not come from a benign cause involves subjective clinical judgment. PURPOSE: Our purpose was threefold: (1) to quantify hearing asymmetry distributions in a large group of patients with medically benign forms of hearing loss, stratifying for age, sex, and noise exposure history; (2) to assess how previously proposed hearing asymmetry calculations segregate tumor from nontumor cases; and (3) to present the results of a logistic regression method for defining hearing asymmetry that incorporates age, sex, and noise information. RESEARCH DESIGN: Retrospective chart review. STUDY SAMPLE: Five thousand six hundred and sixty-one patients with idiopathic, age- or noise exposure-related hearing loss and 85 untreated VS patients. DATA COLLECTION AND ANALYSIS: Audiometric, patient history, and clinical impression data were collected from 22,785 consecutive patient visits to the audiology section at Mayo Clinic in Florida from 2006 to 2009 to screen for eligibility. Those eligible were then stratified by VS presence, age, sex, and self-reported noise exposure history. Pure-tone asymmetry distributions were analyzed. Audiometric data from VS diagnoses were used to create four additional audiograms per patient to model the hypothetical development of AHL prior to the actual hearing test. The ability of 11 previously defined hearing asymmetry calculations to distinguish between VS and non-VS cases was described. A logistic regression model was developed that integrated age, sex, and noise exposure history with pure-tone asymmetry data. Regression model performance was then compared to existing asymmetry calculation methods. RESULTS: The 11 existing pure-tone asymmetry calculations varied in tumor detection performance. Age, sex, and noise exposure history helped to predict benign forms of hearing asymmetry. The logistic regression model outperformed existing asymmetry calculations and better accounted for normal age-, sex-, and noise exposure-related asymmetry variability. CONCLUSIONS: Our logistic regression asymmetry method improves the clinician's ability to estimate risk of VS, in part by integrating categorical patient history and numeric test data. This form of modeling can enhance clinical decision making in audiology and otology.

Oculo-vestibular recoupling using galvanic vestibular stimulation to mitigate simulator sickness.

INTRODUCTION: Despite improvement in the computational capabilities of visual displays in flight simulators, intersensory visual-vestibular conflict remains the leading cause of simulator sickness (SS). By using galvanic vestibular stimulation (GVS), the vestibular system can be synchronized with a moving visual field in order to lessen the mismatch of sensory inputs thought to result in SS. METHODS: A multisite electrode array was used to deliver combinations of GVS in 21 normal subjects. Optimal electrode combinations were identified and used to establish GVS dose-response predictions for the perception of roll, pitch, and yaw. Based on these data, an algorithm was then implemented in flight simulator hardware in order to synchronize visual and GVS-induced vestibular sensations (oculo-vestibular-recoupled or OVR simulation). Subjects were then randomly exposed to flight simulation either with or without OVR simulation. A self-report SS checklist was administered to all subjects after each session. An overall SS score was calculated for each category of symptoms for both groups. RESULTS: The analysis of GVS stimulation data yielded six unique combinations of electrode positions inducing motion perceptions in the three rotational axes. This provided the algorithm used for OVR simulation. The overall SS scores for gastrointestinal, central, and peripheral categories were 17%, 22.4%, and 20% for the Control group and 6.3%, 20%, and 8% for the OVR group, respectively. CONCLUSIONS: When virtual head signals produced by GVS are synchronized to the speed and direction of a moving visual field, manifestations of induced SS in a cockpit flight simulator are significantly reduced.

The effect of galvanic vestibular stimulation on distortion product otoacoustic emissions.

Galvanic stimulation has long been used as a nonmechanical means of activating the vestibular apparatus through direct action on the vestibular nerve endings. This stimulation has been reported to be safe, but no studies have examined the potential changes in the corresponding cochlear receptors. The aim of the present study was to evaluate the effect of galvanic vestibular stimulation (GVS) on distortion product otoacoustic emissions (DPOAEs). Fourteen subjects underwent DPOAEs during several conditions of GVS. The DPOAEs ranged from ∼ 1 kHz to ∼ 8 kHz at 65/55 dB for f1/f2 and with an f2/f1 ratio of 1.2. The subjects were evaluated at 10 stimulation conditions that ranged from -2.0 mA to +2.0 mA for each frequency. Statistical analysis showed no significant differences in DPOAE amplitudes for all conditions with and without GVS. Results also showed no significant differences between DPOAE amplitudes before and after GVS. Multivariate analysis found subject variability in DPOAE amplitude, which was not thought to be GVS related. Results indicated that GVS produced neither temporary nor permanent changes in DPOAEs.

Superficial siderosis of the central nervous system: phenotype and implications for audiology and otology.

OBJECTIVE: Superficial siderosis of the central nervous system (SSCN) results after chronic subarachnoid hemorrhage. Consequent demyelination, particularly of the cochleovestibular nerve and cerebellum, causes auditory-vestibular dysfunction. Predominant symptoms include progressive sensorineural hearing loss, imbalance, and ataxia. Despite characteristic auditory-vestibular involvement, SSCN is not well known among the hearing health community. STUDY DESIGN: Clinical records of 49 patients diagnosed with SSCN were reviewed. Analysis included review of demographic, audiometric, and vestibular data of the largest sample to date and comparison to 31 audiovestibular case reports in the literature. RESULTS: Hearing loss and disordered balance were reported by 92% and 67% of patients, respectively. Results suggest variable but substantial auditory-vestibular involvement related to SSCN. Hearing loss is typically progressive, sloping, and asymmetric and exceeds hearing loss expected based on age or sex. Decreased word recognition is possible and traditional amplification may fail to provide benefit. CONCLUSION: SSCN is a destructive disorder affecting the auditory-vestibular system. Although not a common diagnosis, SSCN may be more prevalent than clinicians realize. Site of lesion may be anywhere within the auditory-vestibular system from the inner ear to the cortex, although the cochleovestibular nerve and cerebellum are particularly vulnerable. The progressive retrocochlear nature of the disorder makes differential diagnosis difficult and development of effective treatment options challenging. It is essential that audiologists and otologists recognize this uncommon cause of sensorineural hearing loss and balance disorder and the implications for evaluation, treatment, and counseling.

Hypoxia-induced changes in standing balance.

BACKGROUND: A few studies in the literature have reported postural changes with hypoxia, but none have quantified the magnitude of change. Further understanding of this condition could have implications for patients at risk for falls, individuals undergoing acute altitude exposure, and pilots and commercial passengers. The objective of this study was to evaluate the effect of different levels of hypoxia (oxygen nitrogen mixtures) on postural standing balance using the computerized dynamic posturography (CDP) system. This improves upon previous protocols by manipulating vision and standing balance with a sway-referenced visual field and/or platform. Additionally, normative data were available for comparison with the cumulative test scores and scores for each condition. METHODS: Altitude hypoxia was simulated by use of admixing nitrogen to the breathing gas to achieve equivalent altitudes of 1524 m, 2438 m, and 3048 m. Subjects were evaluated using the CDP system. RESULTS: Subjects showed an overall trend toward decreased performance at higher simulated altitudes consistent with the initial hypothesis. Composite standing balance sway scores for the sensory organization subtest of CDP were decreased compared to baseline for simulated altitudes as low as 2438 m (mean sway scores: 81.92 at baseline; 81.85 at 1524 m; 79.15 at 2438 m; 79.15 at 3048 m). Reaction times to unexpected movements in the support surface for the motor control subtest (MCT) increased compared to baseline (mean composite scores: 133.3 at baseline; 135.9 ms at 1524 m; 138.0 ms at 2438 m; 140.9 ms at 3048 m). CONCLUSIONS: The CDP testing provided a reliable objective measurement of degradation of balance under hypoxic conditions.

Phase 2 study examining magnesium-dependent tinnitus.

BACKGROUND: Recent studies in noise-induced and idiopathic sensorineural hearing loss have suggested that magnesium supplementation may lessen both hearing loss and the severity of tinnitus in patients. Further epidemiological evidence indicates that all age groups of Americans fall short of the recommended daily allowance for magnesium by 100 mg daily. PURPOSE: The purpose of this study was to examine any potential benefit in lessening the severity of tinnitus in patients taking supplemental magnesium. RESEARCH DESIGN: The study was a single-arm, open-label, before-and-after study of oral magnesium (532 mg per day) in 26 patients for 3 months. Tinnitus severity was evaluated and recorded daily by the patient using the Tinnitus Distress Rating (TDR) scale of 0 (no tinnitus) to 10 (worst possible tinnitus). The Tinnitus Handicap Inventory (THI) was administered before and at the end of the study, and scores were converted to the grades of the 5-item Tinnitus Severity Scale (TSS). The purpose of this phase 2 study was to investigate whether the treatment was effective at all, and, as such, a placebo control was not performed. All data were collected at Mayo Clinic in Scottsdale, Arizona, between March 6 and December 10, 2008. STUDY SAMPLE: Patients with moderate to very severe tinnitus (TDR score of 3 through 8). INTERVENTION: Daily magnesium supplementation, 532 mg; patient completion of the THI; and daily self-report of TDR. DATA COLLECTION AND ANALYSIS: The main outcome measures were mean TDR scale scores and THI scores as converted to TSS grades. The primary analysis was done on the basis of intention to treat. RESULTS: Twenty-six patients were enrolled; 19 completed the study. The extent of handicap, as measured by THI/TSS, for subjects with slight or greater impairment was significantly decreased (P=.03). Patients who ranked slight or greater on the THI/TSS before intervention showed a significant decrease in the severity of their tinnitus at post-testing (P=.008). CONCLUSION: The results suggest that magnesium may have a beneficial effect on perception of tinnitus-related handicap when scored with the THI.

Negative effect of deep cochlear implant electrode insertion on speech perception.

This case study details the evaluation, explantation, and subsequent reimplantation of a cochlear implant (CI) recipient with an unusually deep electrode array insertion. Although the positive value of sufficiently deep insertion and the effect of insertion variability have been researched, there are few data available that illustrate the detrimental effects on speech recognition when deep insertion corrupts optimal use of the CI. This unique case report challenges the assumption that deeper insertion will result in improved speech understanding and demonstrates the importance of fully evaluating recipients' complaints and recognizing the impact of frequency-to-place mismatch.

Cochlear implant patients with superficial siderosis.

BACKGROUND: Considered a rare disorder, superficial siderosis of the central nervous system (SSCN) has become more frequently diagnosed in recent years. As it is characterized by progressive sensorineural hearing loss, patients' needs may surpass the capability of hearing aid technology. Despite the retrocochlear nature of the disorder, patients have undergone cochlear implantation (CI) with varying success. PURPOSE: To summarize the issues surrounding cochlear implant candidates with SSCN as well as highlight trends in performance postimplantation. RESEARCH DESIGN: Retrospective case reports of seven cochlear implant candidates detail the symptoms, typical audiologic presentation, and array of clinical issues for patients with this progressive and potentially fatal disease. RESULTS: Despite the retrocochlear component of a hearing loss caused by SSCN, cochlear implantation may be a viable option. CONCLUSIONS: It is essential that the CI audiologist not only be aware of the disorder but also be well versed in the resulting implications for the cochlear implant process. A more thorough case history, an expanded candidacy test battery, and knowledge of the typical presentation of SSCN are critical. The diagnosis of SSCN will impact expectations for success with the cochlear implant, and counseling should be adjusted accordingly.

Magnesium and hearing.

The last several decades have revealed clinical and experimental data regarding the importance of magnesium (Mg) in hearing. Increased susceptibility to noise damage, ototoxicity, and auditory hyperexcitability are linked to states of Mg deficiency. Evidence for these processes has come slowly and direct effects have remained elusive because plasma Mg levels do not always correlate with its deficiency. Despite the major progress in the understanding of cochlear mechanical and auditory nerve function, the neurochemical and pharmacologic role of Mg is not clear. The putative mechanism suggests that Mg deficiency may contribute to a metabolic cellular cascade of events. Mg deficiency leads to an increased permeability of the calcium channel in the hair cells with a consequent over influx of calcium, an increased release of glutamate via exocytosis, and over stimulation of NMDA receptors on the auditory nerve. This paper provides a current overview of relevant Mg metabolism and deficiency and its influence on hearing.