Extra- and intra-axial brain stem auditory disorders

Auditory skills of figure-ground and closure in air traffic controllers

PURPOSE

To investigate the auditory skills of closure and figure-ground and factors associated with health, communication, and attention in air traffic controllers, and compare these variables with those of other civil and military servants.

METHODS

Study participants were sixty adults with normal audiometric thresholds divided into two groups matched for age and gender: study group (SG), comprising 30 air traffic controllers and control group (CG), composed of 30 other military and civil servants. All participants were asked a number of questions regarding their health, communication, and attention, and underwent the Speech-in-Noise Test (SIN) to assess their closure skills and the Synthetic Sentence Identification Test - Ipsilateral Competitive Message (SSI-ICM) in monotic listening to evaluate their figure-ground abilities. Data were compared using nonparametric statistical tests and logistic regression analysis.

RESULTS

More individuals in the SG reported fatigue and/or burnout and work-related stress and showed better performance than that of individuals in the CG for the figure-ground ability. Both groups performed similarly and satisfactorily in the other hearing tests. The odds ratio for participants belonging in the SG was 5.59 and 1.24 times regarding work-related stress and SSI-ICM (right ear), respectively.

CONCLUSION

Results for the variables auditory closure, self-reported health, attention, and communication were similar in both groups. The SG presented significantly better performance in auditory figure-ground compared with that of the CG. Self-reported stress and right-ear SSI-ICM were significant predictors of individuals belonging to the SG.

Hearing disorders in brainstem lesions

Auditory processing can be disrupted by brainstem lesions. It is estimated that approximately 57% of brainstem lesions are associated with auditory disorders. However diseases of the brainstem usually involve many structures, producing a plethora of other neurologic deficits, often relegating "auditory symptoms in the background." Lesions below or within the cochlear nuclei result in ipsilateral auditory-processing abnormalities detected in routine testing; disorders rostral to the cochlear nuclei may result in bilateral abnormalities or may be silent. Lesions in the superior olivary complex and trapezoid body show a mixture of ipsilateral, contralateral, and bilateral abnormalities, whereas lesions of the lateral lemniscus, inferior colliculus, and medial geniculate body do not affect peripheral auditory processing and result in predominantly subtle contralateral abnormalities that may be missed by routine auditory testing. In these cases psychophysical methods developed for the evaluation of central auditory function should be employed (e.g., dichotic listening, interaural time perception, sound localization). The extensive connections of the auditory brainstem nuclei not only are responsible for binaural interaction but also assure redundancy in the system. This redundancy may explain why small brainstem lesions are sometimes clinically silent. Any disorder of the brainstem (e.g., neoplasms, vascular disorders, infections, trauma, demyelinating disorders, neurodegenerative diseases, malformations) that involves the auditory pathways and/or centers may produce hearing abnormalities.

Auditory measures in clinically depressed individuals. II. Auditory evoked potentials and behavioral speech tests

This is the second paper in a series of two papers comparing auditory measures in depressed and non-depressed individuals. In this paper, we describe the auditory brainstem responses (ABRs), auditory late responses (ALRs) and behavioral speech measures obtained from the same set of 36 individuals as in our previous paper. No changes were made to the inclusion criteria or subject classification. The results indicated a significantly larger amplitude growth with increase in intensity for ABR peak V and ALR peak N1P2 in the unmedicated group compared to the normal group. The unmedicated group performed less favorably on most behavioral speech tests administered compared to the control group, but the difference was significant only in the left ear for the Low Predictability Sentence List of the R-SPIN (Revised-Speech Perception in Noise) test. The mean test scores of the medicated group were closer to the scores of the control group.

Practice and list effects on the synthetic sentence identification test in young and elderly listeners

A high prevalence of central auditory processing disorders (CAPD) has been reported in the elderly based on scores for the Synthetic Sentence Identification Test (SSI). This study examined practice effects and list differences on the Auditec version of the SSI with an ipsilateral competing message in 30 young and 20 elderly participants. Results for the younger participants suggested that a minimum of one practice list should be used with the SSI, whereas results for the elderly participants suggested that a minimum of three practice lists should be used. The binomial model of A. R. Thornton and M. J. M. Raffin (1978) was suggested for use in determining the required number of lists needed to obtain reliable SSI performance. Significant list differences were found with the Auditec version of the SSI. It was recommended to use only Lists A, C, D, E, G, and I for consistent results across lists. Practice effects and list differences should be accounted for when using the SSI for the assessment of CAPD in elderly and young listeners.

Auditory deficits and hearing loss associated with focal brainstem haemorrhage

Four cases of central pontine haemorrhage are described in which auditory dysfunction was documented. Two cases had a hearing loss, in one of which there was recovery of the low frequencies. This case provides support for the tonotopic organization of the auditory pathways in the caudal pontine area, with the lowest frequencies being encoded medially. In all cases, there were abnormalities of the auditory brainstem responses, wave V being consistently involved, while wave III was abnormal in only one patient. In three cases, the masking level differences and crossed acoustic reflex thresholds were abnormal. The ipsilateral reflex thresholds were normal at least on one side in all cases. In the patient with the most significant hearing loss, loudness recruitment, assessed both psychophysically and with the acoustic reflex thresholds, was evident. These data are interpreted in terms of there being damage to the medial superior olivary nuclei and trapezoid body involving both afferent and efferent fibres.

The value of combining auditory brainstem responses and acoustic reflex threshold measurements in neuro-otological diagnosis

Acoustic reflex thresholds (ART) and auditory brainstem responses (ABR) were measured in 69 patients referred to the Neuro-otological clinic on the suspicion of a retrocochlear lesion. The pure-tone selection criterion was an average hearing loss of less than 60 dB at 0.5, 1, 2, and 4 kHz, with no thresholds exceeding 70 dB and only one threshold exceeding 60 dB. Both tests proved independently to be most effective in the diagnosis of cerebello-pontine angle (CPA) tumours and to a lesser extent for brainstem lesions. The ABR was positive in 100% of CPA group and 90% in the brainstem group compared with 93% and 70% respectively for the ART. The combination of the two tests provides patterns of abnormality which are more disease specific. In the CPA cases the most common and consistent patterns of abnormality were the unilateral delay of Wave V or III and V of the ABR associated with a vertical ART pattern indicative of an abnormality of the ipsi and contralateral reflexes on stimulating the affected side. Intrinsic brainstem lesions most commonly resulted in bilateral ABR abnormalities combined with the full-house ART pattern indicative of bilateral abnormalities of both ipsi and contralateral reflexes.

Auditory brain stem responses and nonsense monosyllable perception test findings for patients with auditory nerve and brain stem lesions

A nonsense monosyllable audiometric test was administered to 15 patients with eighth nerve or brain stem disorders caused by tumor, hemorrhage, encephalitis, and degenerative disease. Auditory brain stem responses (ABR) were abnormal in all patients. ABR abnormalities were defined by the absence of some or all waves or by prolongation of the wave V-I interval. The discrimination scores of the nonsense monosyllables were significantly lower in patients with completely absent ABR, with partial ABR series involving wave I, or with severely prolonged wave V-I intervals (over 3 SD). However, in patients with wave I only or with only moderately prolonged wave V-I intervals (less than 3 SD), test scores were within normal range. It is concluded that: 1. perception of nonsense monosyllables could be, though need not be, affected in patients with brain stem lesions; 2. eighth nerve lesions severely disrupt auditory comprehension as well as perception of nonsense monosyllables.