Effect of hearing aid experience on preferred insertion gain selection

The effect of hearing aid experience (measured as years of hearing aid use and user insertion gain at octave frequencies from 250 Hz to 4000 Hz) on the selection of preferred insertion gain under six listening conditions and one vocalization condition was examined. Thirteen experienced hearing aid users selected their preferred insertion gain in each test condition using a modified simplex procedure. The results showed that for the listening conditions, preferred insertion gain was highly correlated with the subjects' hearing loss from 500 Hz to 2000 Hz. Hearing aid experience did not correlate at all with preferred insertion gain. On the other hand, user insertion gain at 250 Hz and 500 Hz correlated highly with preferred insertion gain selected during vocalization. Years of hearing aid use did not correlate with preferred insertion gain selection. These results suggest that user insertion gain can affect preferred insertion gain selection only when the test conditions are identical to those that the hearing aid wearers experience in everyday lives. In typical laboratory conditions, preferred insertion gain is likely determined by the stimulus characteristics and subjective preference.

Binaural release from temporal induction

This study examined the effects of interaural phase difference (IPhD) relations in temporal induction (TI)-that is, the perceived continuity of a fainter sound (inducee) through an interrupting higher amplitude sound (inducer). The extent of TI was measured both directly as the upper amplitude level for continuity and indirectly as the loudness reduction of the inducer. It was found that TI was inhibited when the IPhD of the inducer and the IPhD of the inducee differed. It was also found that the extent of induction was positively related to the masking potential of the inducer as measured by the binaural masking level difference procedure. These results suggest that TI involves processes that are affected by interaural phase differences and that the masking potential rule, shown by previous studies to apply in the frequency domain, applies also in the IPhD domain. The present findings are consistent with the hypothesis that TI results from allocation of a portion of the neural excitation produced by the inducer over to the inducee if the inducer has the appropriate masking potential. As a consequence, obliterated signals can be selectively restored on the basis of both frequency-specific monaural cues and azimuth-related binaural cues, abilities that can enhance detection of signals under the noisy conditions of everyday life.

Nonlinearity of mechanoelectrical transduction of outer hair cells as the source of nonlinear basilar-membrane motion and loudness recruitment

The sound-induced travelling wave in the mammalian cochlea is believed to be enhanced and sharpened by a positive-feedback mechanism, causing the passive, linear growth function of the basilar membrane (BM) to become nonlinear. Based on direct measurements of the receptor potential of isolated outer hair cells, it is shown here how nonlinear BM motion might be due predominantly to the nonlinear growth function of the receptor potential. Since intensity coding in the inner ear is supposed to depend on an interaction of nonlinear BM motion with afferent fibres of different synaptic thresholds, intensity coding is expected to be directly dependent on the mechanoelectrical transduction of outer hair cells (OHC). According to the present experimental data and the feedback concept of outer hair cell action, disruption of the mechanoelectrical transduction of OHC leads to both a reduction of gain and linearizing of the response; that is, to both hearing loss and loudness recruitment.

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.

Villchur revisited: another look at automatic gain control simulation of recruiting hearing loss

An algorithm to simulate the effects of sensorineural hearing impairment on speech reception was investigated. Like that described by Villchur [J. Acoust. Soc. Am. 62, 665-674 (1977)], this simulation employs automatic gain control in independent frequency bands to reproduce the elevated audibility thresholds and loudness recruitment that are characteristic of this type of loss. In the present implementation, band gains are controlled in an effort to simulate loudness recruitment directly, using recruitment functions that depend only on the magnitude of hearing loss in the band. In a preliminary evaluation, two normal-hearing subjects listened to the simulation matched to hearing losses studied previously [Zurek and Delhorne, J. Acoust. Soc. Am. 82, 1548-1559 (1987)] with noise-masking simulations. This evaluation indicated that the present automatic gain control simulation yielded scores roughly similar to those of both the hearing-impaired listeners and the masked-normal listeners. In the more-detailed evaluation, the performance of three listeners with severe sensorineural hearing loss on several speech intelligibility tests was compared to that of normal-hearing subjects listening to the output of the simulation. These tests included consonant-vowel syllable identification and sentence keyword identification for several combinations of speech-to-noise ratio, frequency-gain characteristic, and overall level. Generally, the simulation algorithm reproduced speech intelligibility well, though there was a clear trend for the simulation to result in better intelligibility than observed for impaired listeners when high-frequency emphasis placed more of the speech spectrum above threshold at higher frequencies. Also, the hearing-impaired listener with the greatest loss showed the largest discrepancies with the simulation. Overall, however, the simulation provides a very good approximation to speech reception by hearing-impaired listeners. The results of this study, together with previous studies of noise-making simulation, suggest that threshold elevation and recruitment, which are necessary features of a simulation of cochlear hearing loss, can also be largely sufficient for simulating the speech-reception performance of listeners with moderate to severe hearing impairments.

Audible and ultrasonic vocalization elicited by single electrical nociceptive stimuli to the tail in the rat

We describe audible and ultrasonic vocalization elicited in rats by a short electrical pulse applied to the tail. Three types of vocal emissions were recorded: (1) 'peep', characterized by a repartition of energy over a wide range (0-50 kHz) of frequencies without any clear structure; (2) 'chatters', characterized by an audible (frequencies in hearing range of humans) fundamental frequency (2.47 +/- 0.03 kHz) and harmonics; and (3) 'ultrasonic emissions', characterized by a succession of slightly modulated pulses with frequencies in the 20-35 kHz range. Peeps and chatters were never recorded before the application of the stimuli. Several different vocalization patterns were described in terms of these types of responses. Just after the stimulation, all the animals emitted a 1st peep, which was generally (61%) followed by a 2nd one. They appeared with reproducible latencies, durations and envelopes. The envelopes of the audible (peeps and chatters) responses were intensity-dependent. Experimental data (moving the stimulation site, lidocaine injection) indicated that the 1st and 2nd peeps were triggered by two different groups of peripheral fibres with mean conduction velocities of 7.3 +/- 0.8 and 0.7 +/- 0.1 m/sec, respectively. This suggested an involvement of A delta and C fibres. Morphine showed a naloxone-reversible and dose-dependent antinociceptive effect by decreasing the 1st and 2nd peep envelopes. It is concluded that a short stimulus applied to the tail triggers a complex behavioural repertoire. It is proposed that this model will be a useful tool for physiological and pharmacological studies of nociception.

[Occupational hearing loss and study of the recruitment by the brain stem auditory potentials]

We have studied 60 ears initial stage professional acoustic trauma and a hearing loss in the 2,000 and 4,000 frequencies at 30-40 db. We also included in the study 60 normal ears as the control group. In the first group we investigated the recruitment by the SISI test. Watson and Tolan's test, vocal audiometry and Metz's test. Recruitment was considered positive when indicated so by two of four tests. In waves I and V of BERA we have obtained the following results compared to those of the normal ears: Amplitude is similar in both waves, whatever the intensity of the click. Latencies increase with weak clicks, more in wave V, while the become equal with stronger clicks, what means the existence of recruitment. While other tests are not useful or doubtful, BERA are of interest for the study on recruitment in deep hearing loss.

Spatiotemporal encoding of sound level: models for normal encoding and recruitment of loudness

This study explores the hypothesis that sound level is encoded in the spatiotemporal response patterns of auditory nerve (AN) fibers. The temporal properties of AN fiber responses depend upon sound level due to nonlinearities in the auditory periphery. In particular, the compressive nonlinearity of the inner ear introduces systematic changes in the timing of the responses of AN fibers as a function of level. Changes in single fiber responses that depend upon both sound level and characteristic frequency (CF) result in systematic changes in the spatiotemporal response patterns across populations of AN fibers. This study investigates the changes in the spatiotemporal response patterns as a function of level using a computational model for responses of low-frequency AN fibers. A mechanism that could extract information encoded in this form is coincidence detection across AN fibers of different CFs. This study shows that this mechanism could play a role in encoding of sound level for simple and complex stimuli. The model demonstrates that this encoding scheme would be influenced by auditory pathology that affects the peripheral compressive nonlinearity in a way that is consistent with the phenomenon of recruitment of loudness, which often accompanies sensorineural hearing loss.

Comparison of measures of frequency resolution and recruitment in patients undergoing neuro-otological investigation

Loudness recruitment and reduced frequency resolution both occur in cochlear types of hearing loss. One theory of loudness recruitment suggests that, as intensity is coded partly by spread of excitation across the nerve fibre array, recruitment is a direct consequence of the broad spread of excitation associated with poor frequency resolution. The present study investigated the relationship between these two quantities. The study involved a simple measure of frequency resolution (three-point psychoacoustical tuning curve, PTC) and conventional measures of recruitment obtained from patients undergoing neuro-otological investigation. Results from 376 ears of 226 patients without any material conductive impairment are presented. Measures of recruitment included the alternate binaural loudness balance test (ABLB) and estimates of dynamic range given by the sensation levels of the uncomfortable loudness level and the acoustic reflex threshold. Once covariation with hearing threshold level had been accounted for, no clear relationship emerged between frequency resolution and any of the measures of recruitment. This finding does not support the notion that frequency resolution and recruitment are specifically related. Rather, PTCs provide information complementary to measures of recruitment.

Stapedius reflex and EABR thresholds in experienced users of the Nucleus cochlear implant

Evoked auditory brainstem responses (EABR) and stapedius reflex thresholds were established in 7 experienced users of the Nucleus cochlear implant. Even using biphasic 400 microseconds/phase clicks for the EABR, responses were observed in only 5 patients; no stapedius reflex (SR) was seen in 3 patients, 2 of whom had a history of middle-ear disorder. The EABR threshold varied widely between subjective threshold and uncomfortable loudness level (ULL) for the same stimulus. The average SR threshold was found somewhat more consistently at 66% of the dynamic range between threshold and ULL, but grossly overestimated the most comfortable level (MCL) in most cases. To obtain equal loudness at the same current level we suggest that broad clicks (300 microseconds/phase) be used for EABR measurements, thus compensating for the lower repetition rate of EABR stimulus compared with the device fitting stimulus.

Relationships among psychoacoustic judgments, speech understanding ability and self-perceived handicap in tinnitus subjects

Tinnitus is often a disturbing symptom which affects 6-20% of the population. Relationships among tinnitus pitch and loudness judgments, audiometric speech understanding measures and self-perceived handicap were evaluated in a sample of subjects with tinnitus and hearing loss (THL). Data obtained from the THL sample on the audiometric speech measures were compared to the performance of an age-matched hearing loss only (HL) group. Both groups had normal hearing through 1 kHz with a sloping configuration of < or = 20 dB/octave between 2-12 kHz. The THL subjects performed more poorly on the low predictability items of the Speech Perception in Noise Test, suggesting that tinnitus may interfere with the perception of speech signals having reduced linguistic redundancy. The THL subjects rated their tinnitus as annoying at relatively low sensation levels using the pitch-match frequency as the reference tone. Further, significant relationships were found between loudness judgment measures and self-rated annoyance. No predictable relationships were observed between the audiometric speech measures and perceived handicap using the Tinnitus Handicap Questionnaire. These findings support the use of self-report measures in tinnitus patients in that audiometric speech tests alone may be insufficient in describing an individual's reaction to his/her communication breakdowns.

A study of electrical promontory stimulation in tinnitus patients

Electrical promontory stimulation relieved tinnitus in 74 (57.4%) of 129 ears (112 patients). There was no significant difference in etiology of tinnitus, age, average audiogram, or tinnitus frequency between patients who responded to electrical stimulation and those who did not. Most patients who did not respond to the initial stimulation trial did not respond to the subsequent trials, suggesting that the initial response to treatment predicts the subsequent response. Patients who did not respond to repetitive treatment were supposed to be under severe stress.

Vestibular decruitment: an indicator of central pathology?

Torok studied the ratio obtained between the responses to two different heat stimulation intensities of the same temperature. A decrease in response to the strong stimulus (i.e., a diminished ratio) was called "vestibular decruitment," and was regarded as a topodiagnostic indicator of central vestibular lesion, reflecting "adaptation" or "fatigue." The authors studied the reliability of vestibular decruitment obtained by Torok's technique in the indication of central vestibular pathology. Twenty-eight normal individuals and 30 patients previously diagnosed by other methods with diffuse pathology of the central nervous system were evaluated. The results obtained show that the two stimuli used are both supraliminal and of different intensity regarding the labyrinth. In no case was vestibular recruitment obtained. In view of the high percentage of normal individuals (57.14%) who presented vestibular decruitment, we consider the latter to lack topodiagnostic value as an indicator of either central or vestibular pathology; the smaller response to the mass stimulus might be explained by the vestibular habituation phenomenon that occurs on applying Torok's technique in both normal individuals and in patients with central vestibular pathology.

Correcting for factors affecting ABR wave V latency

The latency of auditory brainstem response (ABR) wave V has been shown to be affected by several subject and technical factors. Previous studies have often concluded with a recommendation to account or correct for one or more of these factors when latency is used as a means of detecting retrocochlear dysfunction. This study investigated the effect of subject age, sex, hearing loss and stimulus intensity on ABR wave V latency in a group of 189 clinical subjects in whom retrocochlear disease was effectively excluded. Regression analysis showed that all four factors exerted a significant influence on latency and that hearing loss and intensity were most effectively represented when combined to form a sensation level variable, together with a measure of audiogram slope.

Effect on the speech reception threshold in noise of the recovery time of the compressor in the high-frequency channel of a two-channel aid

This paper describes two experiments in a series evaluating and optimising a hearing aid incorporating two forms of automatic gain control (AGC). The first form is a front-end AGC which is normally slow acting and which compensates for variations in the overall level of speech from one situation to another. The second form of AGC follows the front-end AGC. The signal is split into two frequency bands, and fast-acting AGC is applied in the upper band only. The bands are then recombined. The two experiments described here were aimed at determining the optimum value of the recovery time of the AGC in the high-frequency channel. Speech reception thresholds (SRTs) were measured in the presence of speech-shaped noise as a function of the recovery time, for subjects with mild-to-moderate sensorineural loss. In the first experiment the recovery time was varied over the range 10-80 ms. SRTs tended to be lowest (best) at the shorter recovery times but the effects were small. In the second experiment, the recovery time was varied over the range 5-320 ms. In this case, there was a clear trend for SRTs to increase with increasing recovery time. A recovery time of about 20 ms appears to be optimal.

Comparison of clinical and real-life judgments of loudness discomfort

The purpose of this study was to determine the relationship between the loudness discomfort level (LDL) and real-life impressions of loudness discomfort. LDLs were measured with an established procedure for a variety of stimuli including FM tones, speech noise, and stimuli recorded from two real-life environments, in two groups of subjects. Sound pressure level distributions were measured in each of two environments at the time of subject recruitment, and LDLs were subsequently measured. LDLs were then compared to the sound pressure levels measured in each environment, and to the impressions of loudness discomfort which subjects reported through the use of a questionnaire. Results indicated large discrepancies between LDLs and judgments of loudness discomfort in real-life environments. The LDL does not appear to be an accurate predictor of subjects' impression of loudness discomfort and may not be appropriate for setting the SSPL of hearing aids.

Characterization and simulation of impaired hearing: implications for hearing aid design

This article reviews several aspects of auditory perception that are affected by hearing loss of cochlear origin. It is argued that most of the observed effects can be understood in terms of damage to a physiologically vulnerable active process in the cochlea. In a normal ear, this process enhances sensitivity and frequency selectivity and reduces the slope of the input-output function on the basilar membrane. Damage to the active process in impaired ears leads to reduced sensitivity and frequency selectivity, an abnormally rapid rate of growth of loudness with intensity, reduced temporal integration and, for certain types of stimuli, reduced temporal resolution. The implications and relevance of each of these effects to the design and fitting of hearing aids are discussed.

The quantification of pure-tone audiograms and auditory brain stem evoked responses using mathematical modeling procedures

The relationship between quantified pure-tone audiometric variables (namely, pure-tone audiometric slope and the degree of hearing loss) and the slope of the wave V L-I (latency-intensity) function of the ABR was investigated. The influence of loudness recruitment on the relationship between audiogram slope and the wave V L-I slope was also studied. Fifty-five ears were selected and divided into two groups (a positive Metz group consisting of 35 ears and a negative Metz group comprising 20 ears) for statistical analyses. The results of the study indicated no significant relationship between the audiogram variables and the slope of the wave V L-I function. However, a significant relationship emerged between the degree of hearing loss and the slope of the L-I function. The results also suggested that neither loudness recruitment nor audiometric configuration influenced the slope of the L-I function.

Frequency specificity of the auditory brainstem response elicited by 1,000-Hz filtered clicks

In normal-hearing subjects and in subjects with a flat cochlear hearing loss, auditory brainstem responses (ABR) were recorded at various levels of a 1,000-Hz filtered click stimulus with and without high-pass filtered masking noise. The difference in latency of the major peak in the ABR for the masked and unmasked condition was zero at the ABR threshold. We regard this as proof of the frequency specificity of the 1,000-Hz filtered click-stimulated ABR threshold. The difference between ABR threshold and the subjective puretone threshold at 1,000 Hz amounted to 19 dB in normal-hearing subjects and to 10 dB in subjects with a flat cochlear hearing loss. This is probably related to loss of temporal integration and an abnormal loudness growth (recruitment).

Range and regression, loudness scales, and loudness processing: Toward a context-bound psychophysics

How does context affect basic processes of sensory integration and the implicit psychophysical scales that underlie those processes? Five experiments examined how stimulus range and response regression determine characteristics of (a) psychophysical scales for loudness and (b) 3 kinds of intensity summation: binaural loudness summation, summation of loudness between tones widely spaced in frequency, and temporal loudness summation. Context affected the overt loudness scales in that smaller power-function exponents characterized larger versus smaller range of stimulation and characterized magnitude estimation versus magnitude production. More important, however, context simultaneously affected the degree of loudness integration as measured in terms of matching stimulus levels. Thus, stimulus range and scaling procedure influence not only overt response scales, but measures of underlying intensity processing.

Dichotic, diotic, and monaural summation of loudness: a comprehensive analysis of composition and psychophysical functions

In a series of six experiments, the method of magnitude estimation, constrained by a multivariate model, was used to assess the rules that govern the summation of the loudness of two-tone complexes. This methodology enabled us to specify the amounts of summation and simultaneously to construct the corresponding loudness scales. The components had different frequency separations and in the different experiments were presented (1) dichotically, a different frequency to each ear; (2) diotically, to both ears; and (3) monaurally. Results replicated and in some conditions extended known features of multiple signal processing by the auditory system. Thus, qualitatively different rules of loudness integration appeared. For monaural and diotic modes of stimulation, overall loudness depended on total sound energy within the critical band, but on the simple sum of component loudnesses beyond the critical band. For dichotic presentations, a fully additive rule of loudness summation appeared, regardless of frequency spacing. For the latter (but not the former), loudness summation was perfect, with the underlying loudness scales closely approximating Stevens's sone scale.

Partial masking in electrocutaneous sensation: a model for sensation matching, with applications to loudness recruitment

A model for partial masking and other threshold-elevation effects is presented in the context of a sensation-matching paradigm. The model is applied to an electrocutaneous experiment in which the subjects adjusted stimulus intensity on the right-hand fingertip to match sensation levels of standard stimuli presented to the left fingertip. Concurrent mechanical stimulation on the right fingertip masked sensation magnitude in a way consistent with the model. Similarities between this tactile masking effect and analogous auditory phenomena are explored. When applied to loudness matching, the model describes the general shape of loudness contours and it shows that the steep slopes observed in auditory masking and "recruitment" can be a consequence of a threshold shift alone, without a supranormal growth in loudness. The model also shows that a small response bias can distort plots of sensation matching, leading to the suggestion that some varieties of loudness recruitment may not have a sensory basis.

On the relations of intensity jnd's to loudness and neural noise

It is shown experimentally that, in contradiction of the fundamental concept of Fechner's law, the intensity jnd for auditory sinusoidal signals follows loudness, rather than its derivative with respect to sound intensity. The evidence is obtained by comparing the jnd's of a population with normal hearing to those of a population with hearing loss accompanied by loudness recruitment. Although the recruitment increases the slope of the loudness function, the jnd's of both populations were found to be practically equal when the loudness were equal. The phenomenon is accounted for mathematically by assuming that psychophysically relevant neural noise depends not only on the magnitude of loudness, but also on its derivative with respect to sound intensity. A related derivation accounts for the near miss to Weber's law.

A comparison of different methods for assessing the 'intensity' of tinnitus

Questions are raised about the technical and psychological interpretation of loudness match measures in the assessment of tinnitus "intensity". The effect of hearing threshold on loudness matches expressed in sensation level (SL) was investigated by selecting subjects with different degrees of hearing loss. The loudness match expressed in SL was found to be a function of threshold. Correlations were then determined between psychological scales of tinnitus complaint (reported loudness, distress, intrusiveness, and others) and loudness match expressed in HL, SL, sones, or personal loudness units (PLUs). Only matches expressed in PLUs were significantly correlated with reported loudness or other psychological scales. The PLU transformation, derived from an individually determined loudness function, produces values that are generally independent of other audiometric measures. It is therefore recommended for assessing tinnitus "intensity".

Magnitude estimation of loudness. II: Loudness perception in presbycusic listeners

Because clinical methods most commonly used for assessing loudness are indirect measures that require one normal or near normal ear, loudness perception has not been studied thoroughly in listeners with symmetrical hearing loss. In this investigation, loudness perception was studied in three groups of listeners: normal listeners, listeners with asymmetrical sensorineural hearing loss, and individuals with bilaterally symmetrical hearing impairment due to presbycusis. In Experiment 1, a Magnitude Estimation of Loudness (ME) technique was compared to Alternate Binaural Loudness Balance ( ABLB ) results for subjects with asymmetrical hearing impairment. Results indicate that ME and ABLB measurements produce similar evidence of abnormally rapid growth of loudness in asymmetrically impaired listeners. In Experiment 2, loudness growth in individuals with normal hearing or with presbycusic hearing impairment was determined from ME measurements. Although presbycusic subjects tended to have steeper loudness functions than normal subjects, the differences did not reach statistical significance except at 6000 Hz, suggesting that, as a group, presbycusic listeners display little, if any, recruitment of loudness.

Compound action potential input-output decruitment. Effect of topically applied antiseptics

The ototoxic effect of povidone-iodine antiseptics topically applied to the chinchilla round window was examined with particular emphasis on the action potential (AP) input-output function at 2 and 4 kHz. A group of chinchillas exhibited a marked elevation of AP threshold at 8 and 12 kHz, with only a slight threshold elevation at 2 and 4 kHz. A distinct decruitment (less than normal growth of response with increasing sound intensity) of the AP input-output function was, however, found at the lower frequencies. There are implications of an ototoxically induced high-frequency hearing loss on speech frequencies.

Loudness recruitment: contributing mechanisms as revealed by cochlear AP measures in man

A measure of the (average) rate of discharge versus intensity function of cochlear fibers can be obtained from cochlear-evoked compound action potentials using a tone-on-tone forward masking technique. The rationale for the method is presented. This technique was used to investigate, indirectly, cochlear fiber responses in human subjects, both with normal hearing and with deafness of cochlear origin and showing signs of loudness recruitment. In animals with pathologic cochleas, and change in rate of fiber discharge with intensity is more rapid than in normal animals. The present study confirms that this also is the case in human cochlear pathology and suggests that this abnormal steepening of rate versus intensity functions contributes to the phenomenon of loudness recruitment.

[Occupational hearing loss as probability diagnosis (author's transl)]

The paper discusses the question of which factors that are to be taken into consideration are of relevance to the expert in making his differential diagnosis in cases of occupational hearing loss. On the basis of the medical literature and earlier investigations the discussion is concerned with the proof of recruitment as well as with the effects of the exposure level and the exposure duration. Special reference is made to the "typical" hearing-threshold curve. The result of the examination with factor-analysis of 14,684 pure tone audiograms suggests that a small involvement of low and medium frequencies in the hearing loss is especially typical of occupational hearing losses. Not even this method permits delineating the effects of age on hearing from those of exposure to noise. The varying (pathogenetic) exposure level has a strikingly low influence on the extent of the occupational hearing loss. The entire data resulting from 25.544 pure tone audiograms are furthermore used for the computation of hearing-loss curves of different tail probability (supposing a normal distribution). The expert has thus a means available to estimate the probability of whether or not a concrete case is still a typical example of occupational hearing loss.

Auditory dysfunction with facial paralysis

A series of 58 patients with idiopathic facial paralysis were studied to determine if a concomitant cochlear or eight nerve auditory dysfunction could be identified with traditional audiologic tests. Results indicated that only those patients with a facial nerve lesion, proximal to the stapedius branch, experienced reduced tolerance for loud sounds, reduction of speech discrimination at high-intensity levels, and abnormal loudness growth. Such findings suggest that changes in auditory function, accompanying facial nerve paralysis, are a mechanical effect due to absence of stapedial action. Site of lesion tests in this sample failed to demonstrate eighth nerve dysfunction and, thus, does not support a theory of polyneuropathy that involves the auditory nerve.

Observations upon the loudness recruitment phenomenon, with special reference to the differential diagnosis of disorders of the internal ear and eighth nerve

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