Hearing Asymmetry Research Articles

P-1276 - The functional brain's asymmetry according to the dimensional model of schizophrenia

Three clinical “dimensions” are identified for schizophrenia: positive (delusions, hallucinations, thought automatism), disorganization (inappropriate affect, bizarre behavior, formal-thought disorders), negative (affective flattening, alogia, abulia-apathy, anhedonia-asociality). To evaluate Individual Profile of Functional Asymmetry (IPFA) influence on schizophrenia's clinical polymorphism. To compare IPFA in 90 healthy subjects and 90 schizophrenic patients in three clinical groups, depending on prevalence of positive, negative symptoms or disorganization. SAPS/SANS; dichotic listening; test “card with the hole”, “viewing through a telescope”; accuracy of tracking and key press speed tests; SPSS’10.0. The coefficient of right ear (CRE), the coefficient of right hand (CRH) were calculated; seven IPFA types determined by CRH/CRE ratio, depending on function's laterality type and degree. Patients unlike controls revealed: higher frequency of right-sided hearing asymmetry (50% vs. 22%), higher average values of CRE (9,57% vs. 3,1%) and |CRE| (19,98% vs. 10,63%), higher rates of IPFA types with minimal excess |CRH| over |CRE| (less than 5 times) (30% vs.20%) and “inverted” types (|CRE|>|CRH|) (15.5% vs. 5.5%). Controls were more likely to have large predominance of CRH over CRE (more than 5 times) (17.8% vs. 5.6%).Ambidexterity dominated in “negative” dimension group, right hand prevailed in others. Positive symptoms degree directly correlated with CRE. “Negative” type inversely correlated with CRH and |CRH|. Increased right-sided hearing asymmetry points to verbal agnosia of signals coming from the left-side auditory space, which is more related to positive symptoms; negative symptoms are more related to motor function's symmetry. Protective and promoting IPFA types determined.

Safety of Audiology Direct Access for Medicare Patients Complaining of Impaired Hearing

Allowing Medicare beneficiaries to self-refer to audiologists for evaluation of hearing loss has been advocated as a cost-effective service delivery model. Resistance to audiology direct access is based, in part, on the concern that audiologists might miss significant otologic conditions. To evaluate the relative safety of audiology direct access by comparing the treatment plans of audiologists and otolaryngologists in a large group of Medicare-eligible patients seeking hearing evaluation. Retrospective chart review study comparing assessment and treatment plans developed by audiologists and otolaryngologists. 1550 records comprising all Medicare eligible patients referred to the Audiology Section of the Mayo Clinic Florida in 2007 with a primary complaint of hearing impairment. Assessment and treatment plans were compiled from the electronic medical record and placed in a secured database. Records of patients seen jointly by audiology and otolaryngology practitioners (Group 1: 352 cases) were reviewed by four blinded reviewers, two otolaryngologists and two audiologists, who judged whether the audiologist treatment plan, if followed, would have missed conditions identified and addressed in the otolaryngologist's treatment plan. Records of patients seen by audiology but not otolaryngology (Group 2: 1198 cases) were evaluated by a neurotologist who judged whether the patient should have seen an otolaryngologist based on the audiologist's documentation and test results. Additionally, the audiologist and reviewing neurotologist judgments about hearing asymmetry were compared to two mathematical measures of hearing asymmetry (Charing Cross and AAO-HNS [American Academy of Otolaryngology-Head and Neck Surgery] calculations). In the analysis of Group 1 records, the jury of four judges found no audiology discrepant treatment plans in over 95% of cases. In no case where a judge identified a discrepancy in treatment plans did the audiologist plan risk missing conditions associated with significant mortality or morbidity that were subsequently identified by the otolaryngologist. In the analysis of Group 2 records, the neurotologist judged that audiology services alone were all that was required in 78% of cases. An additional 9% of cases were referred for subsequent medical evaluation. The majority of remaining patients had hearing asymmetries. Some were evaluated by otolaryngology for hearing asymmetry in the past with no interval changes, and others were consistent with noise exposure history. In 0.33% of cases, unexplained hearing asymmetry was potentially missed by the audiologist. Audiologists and the neurotologist demonstrated comparable accuracy in identifying Charing Cross and AAO-HNS pure-tone asymmetries. Of study patients evaluated for hearing problems in the one-year period of this study, the majority (95%) ultimately required audiological services, and in most of these cases, audiological services were the only hearing health-care services that were needed. Audiologist treatment plans did not differ substantially from otolaryngologist plans for the same condition; there was no convincing evidence that audiologists missed significant symptoms of otologic disease; and there was strong evidence that audiologists referred to otolaryngology when appropriate. These findings are consistent with the premise that audiology direct access would not pose a safety risk to Medicare beneficiaries complaining of hearing impairment.

Effects of Sex, Age and Hearing Asymmetry on the Interaural Differences of Auditory Brainstem Responses

Healthy patients with asymmetric sensorineural hearing loss who had received examination of auditory brainstem responses (ABR) were gathered for retrospective analysis. The effects of sex, age and hearing asymmetry on the interaural differences of ipsilateral ABR were determined by multivariant linear regression. Our results showed that the interaural differences of ABR wave III and wave V latencies were significantly affected by hearing asymmetry but not by sex or age. However, in female subjects younger than 50 years, differences of III-V intervals could be negatively correlated with hearing asymmetry. We suggest that plasticity in the auditory brainstem in younger females might account for asymmetrical peripheral hearing in this group.

Hearing loss as a risk factor for agricultural injuries

Previous studies suggested that hearing impairment based on self-report might increase the risk of agricultural injuries. However, self-reported hearing measures may be subject to inaccuracy and subjective perception. We assessed the association of agricultural injuries with hearing loss and other hearing characteristics using measured hearing. Study subjects were 150 farmers who participated in the Iowa Certified Safe Farm study. Injury information was collected by telephone interviews at 2-5 month intervals from September 1999 to October 2002. Hearing levels were measured annually using the pure tone audiometry from 1998 to 2002. Adjusted rate ratios of injuries were calculated using the multivariate Poisson regression model. Hearing loss in the better ear (RR = 1.62), hearing asymmetry (RR = 1.67), and fair/poor self-reported hearing (RR = 1.96) were significantly associated with the risk of agricultural injuries. It is notable that self-reported hearing might be a stronger predictor of injuries than pure tone audiometry (PTA). Exposure to noise elevated the risk of injuries in those farmers with hearing loss or hearing asymmetry. The occasional use of hearing protection was significantly associated with agricultural injuries. This study adds substantial evidence that hearing loss acts as a risk for agricultural injuries. Prevention of hearing loss and noise exposure may be important in reducing the burden of agricultural injuries.

Effects of varying unilateral conductive hearing losses on speech-in-noise discrimination: an experimental study with implications for surgical correction.

Unilateral conductive hearing loss (HL) causes measurable disability in realistic hearing environments. The benefits of improving this loss depend both on the absolute level of final hearing and on hearing asymmetry. Surgical success is often measured by the degree of change in the air-bone gap or in the air thresholds. The Glasgow Benefit Plot and the Belfast Rule of Thumb suggest that a given hearing gain will be of greater benefit if the postoperative thresholds in the worse ear are a <30-dB HL or within 15 dB of the contralateral ear. This assertion has important surgical implications, but few audiometric data supporting it currently exist. Speech-in-noise sound-field scores were measured in 16 normal volunteers at three presentation levels at two signal-to-noise ratios (SNRs). Two levels of unilateral conductive HL were simulated with earplugs, averaging 25-and 43-dB HL, respectively, and the effect on speech-in-noise scores was measured and analyzed. Unilateral conductive HL is a disadvantage at lower sound intensities and low SNRs, but it can be compensated for by increasing volume or SNR. The benefits of improving unilateral conductive HL are greater if the final asymmetry is <25 dB and the final hearing threshold is <25 dB. Unilateral conductive HL is a significant disadvantage at low SNRs or presentation volumes. The benefits of surgery to improve HL depend not only on the degree of hearing improvement but also on the final hearing threshold in both ears.

Evidence of Peripheral Hearing Asymmetry in Humans: Clinical Implications

Auditory system hemispheric asymmetry in language processing is well-established, and there are many indications of lateralization as of the peripheral auditory system i.e., as of the cochlea. The left ear is more susceptible to noise damage; tinnitus is more predominant there, while spontaneous otoacoustic emissions (SOAEs) are more often found in the right ear. The present study addressed the following two questions: Does this right-ear SOAE prevalence exist as early as preterm birth? Is there any functional asymmetry in the medial olivo-cochlear (MOC) efferent system, known to modulate outer hair cell contractions? The study involved 483 preterm neonates (gestional age: 24-37 weeks) and 70 right-handed adults (age: 18-31 years). In each ear, SOAEs and evoked otoacoustic emissions (EOAEs) were recorded and analysed, and, for the adults, functional MOC system assessment was made. Results showed SOAEs and EOAE amplitude to be right-predominant and in adults a right MOC functional predominance. These results indicate peripheral auditory system lateralisation, and an early origin thereof. The MOC system being thought to play a protective role, its physiological lateralisation may be relevant to the left prevalence of tinnitus and of auditory fatigue.

Hearing Asymmetry Among Occupationally Noise-Exposed Men and Women Under 60 Years of Age

Interaural asymmetry of hearing thresholds at 4 kHz was analysed in four populations exposed to occupational noise. The left ear was found to be on average significantly worse than the right ear, among both the male and female subjects. In the male population the left ear was twice as often the worse ear as the right one. In the female population the corresponding ratio was 1.5. The average inferiority of the left ear increased as a function of the hearing threshold level. Among subjects with abundant shooting (reindeer herders) the average inferiority of the left ear was close to the average of all male subjects. Interaural difference increased as a function of the hearing threshold level, both among subjects with the left ear and subjects with the right ear being the worse one. In the male population the interaural difference was significantly greater in the former than in the latter group of subjects.

Hearing Asymmetry Among Left-Handed and Right-Handed Persons in a Random Population

The possible effect of handedness on hearing threshold asymmetry was analysed in a large random population representing a normal population. The left ear was on an average slightly but significantly poorer than the right ear at high frequencies, especially at 4 kHz, while at low frequencies the right ear was on average poorer than the left ear. A matched control group of the right-handed subjects was formed for 211 left-handed subjects. Among the left-handed subjects the average ear asymmetry resembled the ear asymmetry of the whole population, the right-handed subpopulation, and of the matched control group. In conclusion, it seems that handedness cannot be responsible for the average inferiority of hearing in the left ear at 4-kHz or for the average slight superiority of the left ear at 0.125-0.5 kHz. However, this analysis does not rule out possible minor effects of handedness on ear asymmetry.

Otologic referral in industrial hearing conservation programs.

Baseline and periodic audiometry was performed on noise-exposed workers in 21 industrial plants. Workers showing moderate hearing loss, asymmetry, or significant threshold shifts were referred for otologic evaluation. The overall referral rate was 2.76%. Of 107 referrals, 53% had otologic diagnoses other than noise-induced hearing loss or required specific intervention, or both. The results support the use of criteria at least as stringent as those used in this study.

Letter: Bilateral hearing asymmetry in a large population.

A statistical study was undertaken to determine if there are statistically observable differences in left-right levels of studies reported by the Public Health Service. The results of nonparametric analysis indicate that the two ears are not significantly different in females. Males, both young and mature, demonstrated that the right ear is significantly more often the more sensitive ear to audiometric test tones.