Contralateral auditory stimulation alters acoustic distortion products in humans

It is now generally accepted that otoacoustic emissions (OAE) represent the only objective and non-intrusive means of functional exploration of the active micromechanical characteristics of the outer hair cells of the organ of Corti. Previous studies showed a decrease of the transiently evoked otoacoustic emissions and spontaneous otoacoustic emissions in humans, during acoustic stimulation of the contralateral ear, and attributed this effect to the medial efferent system. Such an effect has been shown on acoustic distortion product otoacoustic distortion emissions (DPOAE) in guinea pigs, but has not been investigated for DPOAEs recorded in humans, although DPOAEs represent the easiest means of exploring active micromechanical cochlear properties both in humans and in laboratory animals. The present study sought to investigate the existence and characteristics of a contralateral auditory stimulation effect on DPOAEs recorded in humans. This study shows that contralateral broad-band noise (BBN) has a suppressive effect on DPOAEs recorded from 0.5 kHz to 5 kHz. This effect is not due to air conduction, as no change in the noise floor occurred under increasing contralateral stimulation, and as no reduction in DPOAE amplitude was obtained in subjects whose contralateral ear was sealed with a plastic ear plug. Moreover, cross-over attenuation by bone transmission has been ruled out, as no change in DPOAE amplitude was recorded in the healthy ear of total unilaterally deaf patients during acoustic stimulation of the deaf ear. The effect seen was not entirely due to the acoustic reflex, as it was found and could indeed be even greater in subjects with no acoustic reflex. Results presented here show that the contralateral BBN effect is greater at low levels of ipsilateral stimulation, which leads us to discuss the involvement of both passive and active mechanisms in DPOAE generation at high stimulation levels. The contralateral BBN effect seems to be greater in mid frequency cochlear regions. There is strong evidence that the medial efferent system is involved and that afferent and efferent inputs are, at least partly, integrated at a brainstem level in order to ensure cochlear interaction. DPOAEs provide an interesting model for functional exploration of the efferent system, since they seem to be the only type of otoacoustic emission that can be recorded in both humans and in the majority of animals, and since results are obtained in the same way from both animals and humans, which allows experimental animal models very close to the human model.     

Spectral frequency and the modulation of the acoustic startle reflex by background noise.

The rat's (Long-Evans) acoustic startle reflex to a high-frequency tone burst (10.5 kHz) was depressed by intense high-frequency band-pass noise (8–26 kHz) but enhanced by low frequency noise (1–2 kHz). However, contrary to the hypothesis that the depression of startle in intense background noise is produced by sensory masking, the reflex to a low-freqency tone burst (at 1 kHz) was depressed by both high- and low-frequency band-pass noise. Two additional hypotheses are offered to supplement sensory masking in order to explain the asymmetry in these data. The first is that the intratympanic reflex, which acts as a high pass filter on acoustic input, is elicited in intense backgrounds. The second is that acoustic startle reflexes elicited by intense low-frequency tones are in part elicited by their high-frequency distortion products and that these distortion products are then masked by high-frequency background noise. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interrelations between transiently evoked otoacoustic emissions, spontaneous otoacoustic emissions and acoustic distortion products in normally hearing subjects

Active cochlear mechanisms and especially outer hair cells seem to be involved in oto-acoustic emissions (OAEs) genesis. This study sought to investigate basic characteristics of spontaneous otoacoustic emissions (SOAEs), click-evoked otoacoustic emissions (TOAEs) and interrelations between SOAEs, TOAEs and 2f1-f2 and 2f2-f1 distortion product OAEs (DPOAEs) in 135 normally hearing subjects. A gender effect was shown on TOAEs and DPOAEs amplitude, and is attributed to the higher incidence of SOAEs in women (58%) than in men (22%). Moreover, SOAEs presence seems to mask the age effect found, especially at high frequency components, on TOAEs amplitude. A general influence of SOAEs on TOAEs and DPOAEs is shown, especially at frequencies ranging from 1 kHz to 3 kHz, collecting more than 66% of the SOAEs peaks recorded. Lastly, correlations between TOAEs frequency band amplitude and 2f1-f2 DPOAEs amplitude, shows frequency specificity, at least at low frequencies (i.e., from 0.5 to 2 kHz) in agreement with previous works suggesting that the 2f1-f2 DPOAEs generation site is at the geometric mean of the primaries. The same correlations calculated with 2f2-f1 DPOAEs amplitude show frequency specificity at low frequencies i.e., at 800 Hz and 1600 Hz. 2f2-f1 DPOAEs in humans are shown to be generated near the 2f2-f1 frequency region on the cochlear partition.     

High-frequency audiometry above 8,000 Hz

Human auditory sensitivity for the frequencies 8, 10, 12, 16, 18, and 20 kHz was examined in a group of 41 female university students ranging in age from 19 to 22 years. The purpose of this study was twofold: to determine the feasibility of high-frequency testing using procedures routinely employed in clinical audiometry and to collect normative data using this procedure on a young adult population. A modified Hughson Westlake procedure was employed and thresholds were obtained for both ears of each subject. It was noted that for the 20-kHz tone only 52% of the subjects tested were able to respond. Statistical analysis revealed no significant threshold differences between right or left ears for all subjects at any frequency. The approach described in the present study provided reliable thresholds and was found to be clinically feasible. Comparisons were made with similar previous studies and the results of the present study were found to be in general, overall agreement.     

Suppression of stimulus frequency otoacoustic emissions

Observations of the suppression of stimulus frequency evoked otoacoustic emissions (SFOAEs) by a second tone were made in human subjects. Measurements were made with the suppressor tone at frequencies and levels at, above, and below the stimulus tone generating the SFOAE. Data were collected with the stimulus tone at a range of levels (20-60 dB SPL), over a range of frequencies and in six different ears, in three subjects. The results were fitted to a phenomenological model, which allowed the data to be expressed as two parameters against the frequency of the suppressor tone. Characteristics of the suppression were examined, in particular the asymmetry between suppression by tones of higher and lower frequency than the tone evoking the SFOAE. At relatively low levels of suppressor tone, suppressors with frequencies higher than the stimulus tone were more effective suppressors than lower frequencies. At higher levels of suppressor tone, the situation was reversed, with lower frequencies being more effective than higher frequencies. These results were discussed in terms of nonlinear interaction between waves in the cochlea. This interpretation was used to estimate the shape of the traveling wave envelope produced by the stimulus tone, from the results of the suppression experiments. It was shown that the estimates of the shapes of the traveling wave envelope were nonlinear, the peak of the envelope becoming sharper at lower levels of stimulus. A simple quantitative model of SFOAE suppression was formulated using concepts of energy flow within the cochlea. This model produced SFOAE suppression results with all the major characteristics of SFOAE suppression from a real, human ear.     

Distortion product otoacoustic emissions for the assessment of auditory sensitivity

Distortion product otoacoustic emissions (DPOAEs) were evaluated in 494 normal and 506 cochlear-impaired human ears, to determine whether DPOAEs depend on factors such as background noise, the shape of the pure tone audiogram, sex and aging, and whether a DPOAE test can perform well in distinguishing normal-hearing from hearing-impaired ears. The amplitudes of DPOAEs were measured at the frequency of 2f1-f2 (f1 < f2, f2/f1 = 1.22, f2 at 1, 2 and 4 kHz) using as stimuli two pure tones at level of 70 dB from an ILO92 Otoacoustic Emission Analyzer. The correlation coefficients between the DPOAE level and the auditory threshold decreased as the background noise levels at 1 kHz and 2 kHz increased. Therefore, it appeared that ears with large background noise levels would be inadequate for the study of DPOAEs predicting the hearing state. The sensitivity (normal-hearing ears identified as normal hearing) and the specificity (hearing-impaired ears identified as hearing impaired) at the equal-sensitivity-specificity condition were 80.7-86.7% at 1, 2 and 4 kHz, and the areas under the receiver operating characteristic (ROC) curves, which were used to estimate the test performance, were 0.88 for 1 kHz, 0.91 for 2 kHz and 0.92 for 4 kHz. Since these results suggest that a DPOAE can be used as a reliable technique for objective auditory tests, it is thought that actual values (DPOAE level: 4.3 dB at 1 kHz, 5.0 dB at 2 kHz and 2.9 dB at 4 kHz) of false-positive (hearing-impaired ears identified as normal hearing) rates corresponding to 5% can be used in clinical evaluation to separate normal hearing from hearing-impaired ears. There was, however, a significant age effect at 4 kHz on DPOAEs in the ears with the same pure tone hearing thresholds, and the areas of the ROC curves in subjects ranging from 10 to 29 years old were larger than in subjects over 50 years (1 kHz: 0.88 to 0.94 versus 0.83 to 0.84, 2 kHz: 0.95 versus 0.89, 4 kHz: 0.95 to 0.96 versus 0.88 to 0.89). Therefore, it is thought that age-adjusted norms may be necessary for the accurate interpretation of DPOAE results.     

Diagnosis of arrhythmogenic right ventricular cardiomyopathy by fourier analysis of gated blood pool single-photon emission tomography

OBJECTIVES: To investigate the effect of frequency of alternating current on electrically induced torque in healthy subjects, and to establish an optimum frequency for motor stimulation. DESIGN: A repeated-measures design using 12 subjects (part 1) and 3 subjects (part 2). SETTING: A laboratory setting was used. PARTICIPANTS: Participants were volunteers who met the inclusion criteria. INTERVENTIONS: Alternating current with carrier frequencies between 1 and 15kHz, modulated at 50Hz, was applied to each subject on two separate occasions. The frequencies were applied in a different random order on each occasion and different random orders were used between subjects. For part 1 of this study, six frequencies were used: 1, 2, 4, 7, 10, and 15kHz. For part 2, three frequencies were used: 1, 4, and 10kHz. MAIN OUTCOME MEASURES: Part 1: The maximum electrically induced torque, defined as the torque induced at the pain threshold, was recorded for each applied frequency. Part 2: The variation of torque with increasing stimulus intensity was recorded for each applied frequency. RESULTS: Highest electrically induced torque was produced at the lowest frequency examined (1kHz). Torque decreased systematically with increasing frequency over the frequency range examined. The rate of increase in torque with applied stimulus intensity was also found to decrease systematically with increasing frequency in a way that depended strongly on the skinfold thickness of the subject. CONCLUSIONS: Electrical stimulators using an alternating current waveform typically use a carrier frequency in the range of 2kHz to 4kHz for motor stimulation. This study shows that carrier frequencies in this range, modulated at 50Hz, are a compromise between comfort and maximum torque production. For maximum comfort with a low torque, a frequency close to 10kHz is indicated. For maximum torque, a lower frequency of alternating current (1kHz or less) is preferable.     

Single olivocochlear neurons in the guinea pig. II. Response plasticity due to noise conditioning

Previous studies have shown that daily, moderate-level sound exposure, or conditioning, can reduce injury from a subsequent high-level noise exposure. We tested the hypothesis that this conditioning produces an increased activity in the olivocochlear efferent reflex, a reflex known to provide protection to the cochlea. Guinea pigs were conditioned by a 10-day intermittent exposure to 2-4 kHz noise at 85 dB sound pressure level. This conditioning is known to reduce damage from a subsequent high-level exposure to the same noise band. Responses to monaural and binaural sound were recorded from single medial olivocochlear (MOC) efferent neurons, and data from conditioned animals were compared with those obtained from unexposed controls. MOC neurons were classified by their response to noise bursts in the ipsilateral or contralateral ears as ipsi units, contra units, or either-ear units. There were no significant differences in the distributions of these unit types between control and conditioned animals. There were also no differences in other responses to monaural stimuli, including the distribution of characteristic frequencies (CFs), the sharpness of tuning, or thresholds at the CF. For binaural sound at high levels, particularly relevant to sound-evoked activation of the MOC reflex during acoustic overstimulation, the firing rates of MOC neurons with CFs just above the conditioning band showed slight (but statistically significant) elevations relative to control animals. Frequency regions just above the conditioning band also demonstrated maximum conditioning-related protection; thus protection could be due, in part, to long-term changes in MOC discharge rates. For binaural sound at low levels, MOC firing rates in conditioned animals also were increased significantly relative to controls. Again, increases were largest for neurons with CFs just above the conditioning band. For equivalent monaural sound, rates were not significantly increased; thus, conditioning appears to increase binaural facilitation by opposite-ear sound. These data indicate that MOC neurons show long-term plasticity in acoustic responsiveness that is dependent on their acoustic history.     

Personal results trial of classification and standardization in clinical impedancemetry (author's transl)

The author analyses the results obtained in clinical impedancemetry for 2,799 ears: tympanometry and study of the acoustico-facial reflex. He proposes a trial of classification of the results. The author states the terminology to be used in impedancemetry according to the different probe tone frequencies of the clinical impedancemeters and the different acoustic stimulations systems in order to obtain the acoustico-facial reflex.     

The effects of amplitude modulation on acoustic reflex decay

The temporal decay of the acoustic reflex provides the basis for an objective audiological test that differentiates cochlear from retrocochlear pathologies. The classic sign of a neural lesion is a rapid decay of the reflex under conditions of pure-tone stimulation for frequencies of 1,000 Hz and below. This restriction to lower frequencies is due to the fact that even normal ears show decay for higher-frequency signals. At present, it is unclear whether the acoustic reflex decay (ARD) seen in normal ears is related to frequency-specific channels or whether the critical variable is the timing information coded within the channels. This study examined ARD in subjects with normal hearing and middle ear function. The degree of ARD was measured for both modulated and unmodulated carrier frequencies of 500, 1,000, 2,000 and 4,000 Hz with amplitude modulation rates of 50-400 Hz. The dependent variable was the half-life of the decaying reflex (ARD 50%) over a 20-second stimulation interval. Significant ARD was present for high-frequency unmodulated carriers but not for low-frequency carriers. For all listeners, ARD was diminished for all modulated stimuli. The results of this study suggest that resistance to ARD is mediated by both the temporal aspects and frequency of a stimulus.     

Cytochemical and biochemical studies on adenylate cyclase activity in preneoplastic and neoplastic liver tissue and cultured liver cells

OBJECTIVE: To assess the accuracy of: 1) distortion product otoacoustic emission (DPOAE) measures for the identification of frequencies at which auditory sensitivity is normal or near normal; and 2) click and nonmasked tone burst-evoked auditory brain stem response (ABR) thresholds for behavioral threshold estimation for children with sensorineural hearing loss characterized by islands of normal sensitivity. DESIGN: DPOAEs and ABRs were recorded from five hearing-impaired and eight normal-hearing pediatric ears. The accuracy with which DPOAEs permitted identification of frequencies at which elevated hearing thresholds were present was examined. ABR and pure-tone threshold differences for the impaired ears were calculated. RESULTS: For three of the five hearing-impaired ears, significant impairments would have been missed based on click-evoked ABR thresholds. One of those hearing-impaired ears provided an essentially normal 500 Hz tone burst-evoked ABR threshold as well. Four of the hearing-impaired ears provided a 500 Hz tone burst-evoked ABR threshold within 10 dB of the respective pure-tone threshold. However, click-evoked ABR and 500 Hz tone burst-evoked ABR threshold data did not adequately delineate the hearing loss configuration for hearing aid frequency response selection. DPOAEs were present at three out of four frequencies from 1000 to 4000 Hz at which sensitivity was normal or near normal (< or =25 dB HL) and absent at 10 out of 11 frequencies at which sensitivity was impaired. The use of DPOAEs to identify frequencies at which sensitivity was normal and the use of tone burst ABR thresholds at frequencies where DPOAEs were absent provided a better estimate of these pure-tone audiograms than was provided by click-evoked and 500 Hz tone burst-evoked ABR thresholds.     

Dip-shaped hearing loss of Békésy audiogram in high school students

Small dip-shaped hearing loss may be frequently observed on Bekesy audiograms in ears without any hearing loss on pure tone audiograms. Hearing tests and otoacoustic emission measurements were performed in club member of 2 senior high schools (K-D School and S-D School), in order to determine any relationship between inner ear impairments and the small dips on Bekesy audiograms. In the kendo, soccer, tennis and orchestral music clubs of K-D School micro-dips in depth over 10 dB were found to have incidences between 40% and 53%, and the micro-dips were distributed in frequencies above 5 kHz. In the of kendo, tennis, brass band and tea ceremony clubs of S-D School the incidences of micro-dips ears were between 30% and 48%, and the micro-dips tended to be distributed in higher frequencies except in the tea ceremony club. The micro-dips in the ears of the tea ceremony club members were distributed over all the frequencies examined, but most of them disappeared when counted for dip size above 15 dB remaining an ear at 7.5 kHz. Incidences of earphone or headphone users as a hobby were in the range of 30 to 70% in members of all clubs. There were no characteristic findings of clubs in the incidences of the earphone or headphone users. The degree of association between the micro-dip ears and the use of earphone or headphone was low. C-EOAEs which had a 6 ms or longer duration of evoked otoacoustic emissions were detected with an incidence of 40 to 65% and there was a significant association between the micro-dip ears and the C-EOAE ears. Incidences of spontaneous otoacoustic emissions were between 26% and 28% in all clubs and there were differences in the incidences between sexes. The frequency distribution of the spontaneous otoacoustic emissions were remarkably different to that of the micro-dips. To determine whether the C-EOAEs express a predisposition to inner ear susceptibility to noise-induced hearing loss and to ascertain that the micro-dip is a precursor notice to noise-induced hearing loss, further follow-up surveys are needed.     

Spontaneous otoacoustic emissions in preterm neonates: prevalence and gender effects

A number of lines of evidence indicate that the human cochlea is fully functional as a mature sound transducer by 6 months of age. However, information about the development of the active cochlear mechanisms and notably the development of outer hair cell (OHC) activity is yet incomplete. Recording and analysis of otoacoustic emissions (OAEs), probably generated by the OHCs of the organ of Corti, have led to a better understanding, in humans, of how sounds are analysed in the cochlea by means of active mechanisms. Evoked OAEs (EOAEs) and spontaneous OAEs (SOAEs), when they can be recorded in full-term and preterm neonates, show different characteristics from those in adults, suggesting that maturation of the peripheral auditory system is incomplete at birth. To learn more about this maturation, using the best-established facts concerning SOAEs in adults, such as their greater prevalence in females and also in right ears, SOAEs were studied in more detail in 81 preterm neonates, from 30 to 40 weeks of conceptional age, all presenting bilateral EOAEs according to objective criteria. The first finding of this study was that SOAEs existed and could be recorded as of 30 weeks of conceptional age in humans. Some SOAE characteristics in preterm neonates, such as prevalence, peak number and acoustic frequencies, showed similarity with full-term neonates. Comparison of other criteria between the two populations, such as greater SOAE prevalence in right ears and higher SOAE peak number in females, suggested that these developmental factors emerge around term in humans. Comparison of SOAE characteristics between male and female preterms suggested that male preterms were less advanced in peripheral auditory development than were female preterms.     

Slow evoked cortical responses to linear frequency ramps of a continuous pure tone

Slow evoked cortical potentials from ten young normal-hearing subjects have been recorded as responses to linear frequency ramps of a continuous pure tone. Frequency changes from 10 to 500 Hz were studied; the rate of frequency change was varied from 0.02 to 50 kHz/s while the duration of the change was varied from 10 to 500 ms. The rate of frequency change was shown to have the greatest bearing on the responses except for frequency ramp durations below 50 ms and frequency changes below 50 Hz. The base frequencies (250-4000 Hz) and sound levels (20-80 dB HL) exerted an influence on the evoked responses that was qualitatively similar to their influence on behavioral thresholds. The direction of the frequency sweep had no significant influence on the evoked responses. A functional model is proposed in which the time derivate of the signal frequency is integrated with an adaptable integration time that is controlled by the rate of the frequency change.     

Comparison of acoustic reflex and behavioral thresholds as a function of stimulus frequency and duration

Threshold-duration functions for the acoustic reflex and threshold-duration functions based upon behavioral measures were obtained on the same group of subjects and compared. The mean temporal integration for the acoustic reflex threshold appears to be comparable to that for the behavioral threshold for stimuli of 500, 1000, and 2000 Hz, but marked individual differences exist in temporal integration of the acoustic reflex. At 4000 Hz, the mean change in the reflex threshold as a function of stimulus duration is significantly greater than the change in the behavioral threshold under the same conditions, suggesting that in the elicitation of the acoustic reflex the auditory system processes energy less efficiently at 4000 Hz than it does at lower frequencies.     

Distortion product otoacoustic emissions in human newborns and adults. I. Frequency effects

This study varied stimulus frequency and recorded distortion product otoacoustic emissions (DPOAEs) in human newborns and adults. Because of outer and middle ear acoustics, the same auditory input resulted in higher newborn stimulus sound pressure levels across a broad frequency range in the occluded outer ear canal. Noise levels in the canal were 5-15 dB lower for adults at frequencies less than about 3 kHz. The 2 f1-f2 DPOAE was the most reliably recorded DPOAE except at the lowest frequencies assessed. At the lowest frequencies the 2 f2-f1 DPOAE was more frequently recorded than any other DPOAE. There were no striking developmental differences in the kinds of DPOAEs that were recorded. The amplitudes of consecutively recorded 2 f1-f2 DPOAEs were generally within 1.5 dB of each other for all age groups (slightly better reproducibility for adults than newborns). The phases of consecutively recorded 2 f1-f2 DPOAEs were generally within 15 degrees of each other (often less than 10 and 5 degrees for newborns and adults respectively). At the highest frequencies assessed (f2 = 4.2-9.9 kHz) all subjects had similar amplitude 2 f1-f2 DPOAEs. At lower frequencies adult 2 f1-f2 amplitudes were significantly less than those of newborns. At the lowest frequencies reliably assessed (f2 = 1.5-2.1 kHz) term newborns had significantly larger 2 f1-f2 DPOAEs than preterm newborns. Newborn and adult 2 f1-f2 DPOAE amplitude X f2/f1, functions were quite similar although there were reliable differences. Age related differences in the outer and middle ears may explain some of the differences in DPOAEs that were observed.     

Cost of illness: an inextricable maze or an aid in decision making? The case of schizophrenia

Distortion-product otoacoustic emissions (DPOAEs) are still undergoing evaluation for clinical use. Although the effects of ageing on otoacoustic emissions have been studied quite extensively in the past, DPOAE response-growth or input-output (I-O) measures, which are well suited as an objective method for monitoring cochlear function at specific frequencies, have been less thoroughly examined. The aim of the present study was to assess the 2f1-f2 DPOAEs in a clinical setting in order to examine the response of 20 normally hearing middle-aged adults and to compare the results with those of 20 people of the same age with ears of sensorineural high-frequency hearing loss (HL). The experiment consisted of two stages. First, the DPOAE-gram was recorded in 1-4-octave steps at a stimulus level of 70 dB SPL over a frequency range of the f2 primary tone which extended from 1.001 to 6.299 kHz. Secondly, in order to elicit DPOAE I-O functions, the two primary stimuli were presented at equilevel intensities ranging from 20 to 71 dB SPL. The stimulus-level step size was 3 dB. The I-O functions were recorded at five separate DPOAE frequencies, with the f2 frequency most closely related to the clinical audiogram (f2 = 1.0, 1.5, 2.0, 4.0 and 6.0 kHz). Two clearly separated portions in the form of the I-O function for normally hearing ears were found. The first portion, in response to primary levels of 60 dB SPL and below, showed a plateau (saturating) behaviour. If primary levels exceeded 60 dB SPL, I-O functions became more linear. The attenuation of the saturation portion of the I-O function in ears with high-frequency HL across the frequency-test range is difficult to explain because elevated behavioural thresholds were observed only for frequencies > 1.5 kHz. Thus, the more linear I-Os associated with the hearing-loss frequencies may indicate deficiencies in the active properties of outer hair cells (OHCs), whereas those for I-Os < 1.5 kHz, where hearing was normal, may indicate a beginning of damage to active OHC micromechanical processes prior to their clinical manifestation. DPOAE recordings from people with high-frequency HL, possibly age-related, supplement recordings of TEOAEs and give complementary information on degenerative changes in the outer hair-cells. DPOAE I-O functions may reveal discrete pathological alterations both in the active cochlear signal processing and in the passive mechanisms of the cochlea prior to their detection by clinical audiometric tests.     

Functional mapping of the U3 small nucleolar RNA from the yeast Saccharomyces cerevisiae

The 2 f1-f2 distortion product otoacoustic emission (DP) was measured in 20 normal hearing subjects and 15 patients with moderate cochlear hearing loss and compared to the pure-tone hearing threshold, measured with the same probe system at the f2 frequencies. DPs were elicited over a wide primary tone level range between L2 = 20 and 65 dB SPL. With decreasing L2, the L1-L2 primary tone level difference was continuously increased according to L1 = 0.4L2 + 39 dB, to account for differences of the primary tone responses at the f2 place. Above 1.5 kHz, DPs were measurable with that paradigm on average within 10 dB of the average hearing threshold in both subject groups. The growth of the DP was compressive in normal hearing subjects, with strong saturation at moderate primary tone levels. In cases of cochlear impairment, reductions of the DP level were greatest at lowest, but smallest at highest stimulus levels, such that the growth of the DP became linearized. The correlation of the DP level to the hearing threshold was found to depend on the stimulus level. Maximal correlations were found in impaired ears at moderate primary tone levels around L2 = 45 dB SPL, but at lowest stimulus levels in normal hearing (L2 = 25 dB SPL). At these levels, 17/20 impaired ears and 14/15 normally hearing ears showed statistically significant correlations. It is concluded that for a clinical application and prediction of the hearing threshold, DPs should be measured not only at high, but also at lower primary tone levels.     

2f1-f2 distortion product otoacoustic emissions in White Leghorn chickens (Gallus domesticus): effects of frequency ratio and relative level

The effects of primary tone frequency ratio (f2/f1 ratio) and relative level (L2/L1) on the amplitude of the cubic difference tone (CDT: 2f1-f2) distortion product otoacoustic emissions (DPOAEs) were investigated in adult White Leghorn chickens (Gallus domesticus). In experiment 1, 9 f2/f1 ratios ranging from 1.05 to 1.8 were investigated. Measurements were obtained from both ears of 4 chickens at 7 f1 frequencies ranging from 0.8 to 4.0 kHz. The primary tones were equal in level, and varied from 20 to 80 dB SPL. The mean CDT amplitude increased with increasing primary tone level once the measurement noise floor was exceeded. The input/ output functions assumed one of two shapes: one in which there was a systematic increase in DPOAE amplitude with increasing primary tone level, and the other in which there was a plateau in the input/output function near 65-70 dB SPL. At the highest primary tone level (80 dB SPL), there was a decrease in the CDT amplitude with increasing f2/f1 ratio. At high primary tone levels, the f2/f1 ratio which produced the largest CDT was 1.05 or 1.1, while at lower primary tone levels the largest CDT occurred at f2/f1 ratios of 1.2-1.3. In experiment 2, L2 was held constant at 70 dB SPL, and L1 varied from 50 to 80 dB SPL. For f1 frequencies of 0.8 and 3.2 kHz, there was an increase in the CDT amplitude with increasing L1, followed by an asymptote at higher levels. In contrast, for 1.6 and 2.0 kHz f1 frequencies, the amplitude increased, plateaued and then increased again at higher levels. Informal measurements suggest that spontaneous otoacoustic emissions (SOAEs) are rarely seen in chickens. However, a reliable SOAE was observed in 1 chicken, which could be suppressed by external sounds and anoxia.     

The electrophysiological indices of the state of the different sections of the auditory analyzer in persons with a normal voice and with functional voice disorders]

Individuals with normal voice and patients with voice functional impairments undergone electrophysiological investigation of various parts of the hearing system, using tone audiometry, including the extended frequency band (10, 12, 14 and 16 kHz), as well as short- and long-latency acoustic evoked potentials (SLAEP and LLAEP). It was found out, that individuals with voice functional impairments had all of their hearing system's parts impaired to various extent, with more marked impairments in the central, rather than in the peripheral part of the hearing system. It was shown, that hearing at 4-8 kHz, as well as with the extended frequency band, especially at 14-16 kHz, time patterns of acoustic evoked potentials (latencies of waves III and V of SLAEP, the interpeak interval I-V, as well as the latency periods of the LLAEP components P2 and N2) could be useful in professional selection of individuals of voice and speech professions and for solving labor expertise matters. Of those individuals with normal voice but systematic vocal stress, 17.5% had impaired hearing at 14 and 16 kHz, as well as significant latency prolongation of the LLAEP wave N2 with tone stimulation at 1 and 4 kHz. Apparently, individuals of voice and speech professions should be referred to as the "risk" group. It may well be, that extended band audiometry and acoustic evoked potentials time patterns could be useful in determining the thresholds between the normality and pathology in voice dysfunctions.