Mismatch negativity and psychoacoustic measures of gap detection in normally hearing subjects.

Temporal auditory processing deficits are thought to play an important role in some pathologies of speech understanding difficulties. The purposes of the present study were to determine whether short silent gaps within a pure tone can be used to elicit mismatch negativity (MMN) as an objective measure of temporal resolution, and to investigate the relation between MMN and performance on a behavioral gap-detection task. The stimuli used for both tasks were 1-kHz sinusoids presented in a low-pass masking noise. Behavioral gap-detection thresholds were determined using an adaptive three-alternative forced-choice procedure. To elicit MMN, a series of deviant stimuli with varying gap durations was generated and presented in an oddball paradigm among standard stimuli without a gap. Only the gaps larger than the mean behavioral gap-detection threshold evoked a clear MMN. There was no clear relation between psychoacoustic and MMN thresholds.

Suppression of tone burst evoked otoacoustic emissions in relation to frequency separation.

Tone burst evoked otoacoustic emissions (TBEOAEs) were measured for two tone bursts presented separately and as a two-tone burst complex to examine the linearity of TBEOAE generators for different frequency separations of the stimuli. The stimuli were: (a) tone bursts of 5-ms duration and center frequencies of 1, 1.5, 2 and 3 kHz; (b) complex stimuli with the 1-kHz tone burst combined digitally with each of the other specified tone bursts. Signals were delivered at 70 dB SPL using a non-linear processing method and at 60 dB SPL using a linear method to 21 ears of normally hearing adults. Spectra of TBEOAEs obtained with single-tone bursts were superimposed (composite) and compared to those of the two-tone burst complex. A close correspondence between the composite and complex spectra was present in all ears. However, the components on the higher-frequency slope of the 1-kHz spectral peak were reduced in the complex spectra obtained with a frequency separation of 0.5 kHz when compared to the corresponding composite spectra. The reduction was greater at a stimulus level of 70 dB SPL than with 60 dB SPL. The effect was smaller for a frequency separation of 1 kHz, and almost absent for the tone burst separation of 2 kHz. Thus, suppression leads to weak non-linear frequency superposition for higher-level, closely spaced stimuli.

[Extended high-frequency audiometry--reproducibility of two type of earphones]. / Die erweiterte Hochfrequenzaudiometrie: Testwiederholbarkeit zweier Kopfhörer.

Auditory thresholds in the frequency range of 0.5-6 kHz and in the extended high-frequency range (8-16 kHz, according to ISO 389-5) were measured for one ear of 139 otologically healthy persons (77 females, 62 males, mean age 25 years, range 12-54 years) using insert earphones ER-2 of Etymotic Research and circumaural earphones HDA 200 of Sennheiser. For each subject, two measures of the thresholds were obtained for both types of transducers during the same test session. Repeatability was significantly worse in the 8-16 kHz region (repeated thresholds were within +/- 5 dB for 90% of the thresholds of each frequency and within +/- 10 dB for 98%), compared to that in the 0.5-6 kHz region (+/- 5 dB for 97%, +/- 10 dB for 100%), as determined by paired t-test and Wilcoxon signed rank test. Repeatability was similar for both transducer types.

Intensity discrimination, temporal integration and gap detection by normally-hearing subjects with weak and strong otoacoustic emissions.

It is unlikely that the overall status of a cochlea and middle ear which produces strong otoacoustic emissions (OAEs), i.e. high-level evoked emissions (EOAEs) and spontaneous emissions (SOAEs), has a generalized effect on peripheral auditory processing if the sensitivity is normal. Current data do not support the hypothesis that a weak OAE profile (low-level EOAEs and no SOAEs) is indicative of subclinical damage to the cochlea. Nevertheless, the ability of a subject to perform some psychoacoustical tasks may be influenced by the interaction between OAEs and test signals. The present experiments investigated the influence of strong or weak OAEs on: (1) intensity just-noticeable differences for pure tones; (2) temporal integration in the vicinity of SOAEs; (3) gap detection thresholds for broad-band noise bursts. The results show that OAEs can influence performance on these psychoacoustical tasks, especially for low-level stimuli with spectral components in the vicinity of high-level SOAEs.

Intracochlear acoustic pressure measurements: transfer functions of the middle ear and cochlear mechanics.

Direct intracochlear acoustic pressure recordings (from 20 to 20,000 Hz) are used to measure the middle-ear transfer functions (forward and reverse) and to better understand the cochlear mechanics in the guinea pig. In the forward direction, the middle-ear transfer function is strongly dependent on the frequency and presents a maximum of +30 dB at 1,000 Hz (bulla open). In the reverse direction, the middle-ear transfer function looks like an ideal reverse middle-ear pressure transformer with -35 dB gain and 0 degrees phase lag from 20 to 8,000 Hz (bulla open, closed ear canal). Passive cochlear mechanics is studied with the help of intracochlear pressure measurements and differential cochlear microphonic potential recordings in the different turns.

Direct evidence of cubic difference tone propagation by intracochlear acoustic pressure measurements in the guinea-pig.

The fine tuning mechanisms involved in the normal processing of sound in the cochlea are non-linear, hence combination tones are generated inside the cochlea when a pair of low-level pure tones with neighbouring frequencies f1 and f2 is used as a stimulus. Their detection as sounds in the ear canal proves that they undergo backward propagation in the cochlea and through the middle ear, and the non-invasive measurement of the combination tone at 2f1-f2, called the cubic difference tone (CDT), has become a routine method of monitoring cochlear function. In order to gain information on the hypothetical places where CDTs are generated, on their intracochlear levels and propagation velocities, direct measurements of CDT pressure waves were carried out in scala vestibuli and tympani of the first and second turn of the guinea-pig cochlea. Cubic difference tones at 2f1-f2 varied from 0.75 to 9 kHz and were measured with a miniature piezoresistive transducer. Its high sensitivity allowed the detection of CDTs whenever their levels exceeded 5 dB SPL in the ear canal, i.e. 40 dB SPL (re: 20 microPa) inside the cochlea. The levels of CDTs were similar in scala vestibuli of the first and second turn. Phase comparisons between measurements at 2f1-f2 in the first and second turn allowed determination of the place where the CDT phase was minimum. It provided an estimation of the generation site of the CDT, which appeared to be close to the place tuned to f2 for stimulus levels lower than 70 dB SPL. Forward and backward travel times from one turn to the other were assessed at several frequencies, and both values were shorter than 0.2 ms. In contrast, the overall 'round-trip' delay of CDTs, measured in the ear canal, was about five times larger, suggesting that local filtering processes rather than propagation delays account for the overall CDT delay.

The influence of disappearing and reappearing spontaneous otoacoustic emissions on one subject's threshold microstructure.

The effects of a consistently disappearing and reappearing spontaneous otoacoustic emission (SOAE) at around 2280 Hz on microstructure for pure tones of varying durations in a 33 year-old woman with normal hearing was studied. The SOAE began to appear after 10-15 min in a quiet test room and increased in level by up to 22 dB over a 30-40-min period. The SOAE was measured every 12 to 15 min. Between measurements, the subject performed a signal detection task for pure tones with total durations varying from 20 to 320 ms. The signal frequencies were within a +/- 30-Hz range relative to the SOAE frequency. For signal durations of 40-320 ms, there was a local dip at the target SOAE frequency when it was either not detectable or its level was lower than -14 dB SPL. Subjective threshold levels were as much as 12 dB better than those obtained when the SOAE was -6 dB SPL or greater. The results suggest that a region of the cochlea with high sensitivity and instability can be put into self-oscillation producing an SOAE, possibly by a change of efferent activity. Hearing threshold is affected possibly due to adaptation or masking.

Reverse middle-ear transfer function in the guinea pig measured with cubic difference tones.

Otoacoustic emissions are increasingly useful for determining cochlear function noninvasively. It is widely agreed that these acoustic signals reflect micromechanical processes in the cochlea. However, their quantitative interpretation requires knowledge of the ways in which vibrations travelling back to the ear canal from the cochlea are shaped by the middle ear. An intracochlear source is needed to derive the reverse middle-ear transfer function (rMETF) by comparing pressure in the external ear canal to the corresponding pressure in scala vestibuli. In the present study, the rMETF was obtained in vivo in the guinea pig using as intracochlear sound source the cubic difference tones (CDTs) generated by a pair of external pure tones. With a closed ear canal and open bulla, the rMETF was found to be flat (-35 dB) over a broad frequency range (1.5-8 kHz). The differences between forward and reverse METF could be explained by different loads acting on the middle ear network, which depends on the direction of signal transmission. With knowledge of the rMETF, it becomes possible to quantify CDTs within the cochlea by measuring them noninvasively in the ear canal.

Distortion product otoacoustic emission test of sensorineural hearing loss: performance regarding sensitivity, specificity and receiver operating characteristics.

The performance of distortion product otoacoustic emissions (DPOEs) as a frequency-specific test of sensorineural hearing loss was evaluated in 142 ears of human adults with normal middle-ear function. The DPOE was measured with the stimulus levels of the two tones equal to 65 dB SPL (re 20 mu Pa) and the ratio between the two frequencies 1.2. In the DPOE test, the cochlear function of an ear at a test frequency was predicted to be normal or abnormal depending upon whether the DPOE level with the geometric mean of the two stimulus frequencies at the test frequency was greater or less than a criterion. The DPOE test outcomes were evaluated against the pure-tone hearing threshold as the standard. We found the sensitivity, specificity and predictive efficiency of the test to be 85-89% at 6000 and 4000 Hz, 82-83% at 2000 Hz and 78-79% at 1000 Hz, respectively. The performance was also evaluated using decision theory in terms of the area under the receiver operating characteristics. The latter was found to range from 0.90 (for 1000 Hz) to 0.94 (for 6000 Hz). These findings support the conclusion that the DPOEs can form a useful frequency-specific objective test of cochlear function.

Longitudinal measurements of distortion-product and click-evoked otoacoustic emissions of preterm infants: preliminary results.

Click-evoked and distortion-product otoacoustic emission (CEOE and DPOE) tests were performed 3-4 times on a weekly basis for 13 ears of 7 preterm infants. The CEOEs and DPOEs recorded from each individual ear were analyzed by calculating the root-mean-square (RMS) levels within half-octave bands and were also compared to the normal ranges defined by the 10th and 90th percentiles of half-octave RMS levels obtained from a group of normal full-term newborn ears. Longitudinal data showed that, in general, CEOE and DPOE RMS levels increased with increasing postconceptional age (PCA) in at least one half-octave band. Combined data from subjects who had both ears tested were collected over multiple sessions. Those data revealed statistically significant correlation between the otoacoustic emission (OE) levels in the two ears of the same individual. The analysis of the combined DPOE and CEOE data showed statistically significant correlation between the RMS DPOE and CEOE levels in each of the half-octave bands in the 2- to 4-kHz region. Pilot measurements of spontaneous otoacoustic emissions (SOEs) indicated an increase of SOE frequencies with increasing PCA of the subject. These findings support the view that postnatal changes occur in the outer, middle, and inner ear of preterm infants. The RMS OE levels of preterm infants were often above the 90th percentiles of full-term newborns suggesting that the maturation of the auditory periphery of preterm infants may possibly pursue a different time course than that of full-term infants.

Otoacoustic emissions in full-term newborns at risk for hearing loss.

Distortion product otoacoustic emissions (DPOEs) and click-evoked otoacoustic emissions (CEOEs) characteristics of the normal newborn population have been previously reported in the literature. There is little information about DPOE evaluations in the newborn population at risk for hearing loss. The authors now report the DPOE and/or CEOE data from six full-term subjects at risk for hearing loss or with highly suspected hearing loss. These subjects were less than 1 year of age and at risk for hearing loss secondary to a history of hereditary hearing loss, meningitis, hyperbilirubinemia, and ototoxic drug exposure. Audiometric evaluation included auditory brainstem responses (ABR), behavioral observation audiometry, and tympanometry. The CEOEs and DPOEs were found to be decreased or absent in the subjects with suspected hearing loss secondary to cochlear pathology; they were found to be normal in a subject with a suspected central hearing loss. This study's data suggest that otoacoustic emissions when combined with ABR can provide a frequency-specific evaluation of cochlear function and help determine the anatomic site of a pathologic lesion.

Distortion-product and click-evoked otoacoustic emissions of preterm and full-term infants.

Full-term and preterm infants were evaluated with click-evoked and distortion-product otoacoustic emissions (CEOEs and DPOEs). The CEOEs and DPOEs recorded from each individual ear were analyzed by calculating the root-mean-square levels within half-octave bands. The fail criterion of the OE tests was that the half-octave RMS DPOE or CEOE levels of an ear under test were below the 10th percentile of full-term newborns in two or more bands. The DPOE data were collected from 118 ears of 61 premature babies; 80 (68%) ears passed the DPOE test, 30 (25%) ears without middle ear effusions failed the test, and 8 (7%) ears with effusions also failed. The CEOE data were collected from 128 ears of 65 premature babies; 102 (80%) ears passed the CEOE test, 18 (14%) ears without middle ear effusions failed the test, and 8 (6%) ears with effusions also failed. In 23 of 80 ears (29%) that passed the DPOE test and in 23 of 102 ears (23%) that passed the CEOE test, RMS OE levels of preterm infants were above the 90th percentile of full-term newborns. The analyses of the combined DPOE and CEOE data obtained from a group of 25 ears of full-term newborns and from a group of 72 ears of preterm babies showed statistically significant correlations between the DPOE and CEOE root-mean-square levels in each of the half-octave bands in the 1.4 to 4 kHz region. For 42 preterm infants tested with auditory brain stem response (ABR), specificity was 86% for CEOE and 74% for DPOE. All infants who failed the ABR also failed OE tests. To the best of our knowledge, this study is the first using combined DPOEs, CEOEs, and ABRs for preterm babies. It showed the feasibility of DPOEs and CEOEs for this population.

Distortion-product and click-evoked otoacoustic emissions of normally-hearing adults.

The purpose of this study was to compare distortion-product otoacoustic emissions (DPOEs) and click-evoked otoacoustic emissions (CEOEs) for normally-hearing human adults. The statistical analysis consisted of computing the DPOE and CEOE levels versus frequency corresponding to the 10th, 25th, 50th, 75th, and 90th percentiles among normal adult ears. The mean and standard deviations of the DPOEs and CEOEs were computed. A direct comparison of the DPOE and CEOE data obtained from the same ears showed that, in a 1-4 kHz frequency region, there was a statistically significant correlation between the levels of the two types of otoacoustic emissions. This finding supports the hypothesis that DPOEs and CEOEs arise from some common mechanisms of the cochlea such as active nonlinear biomechanical mechanisms of the outer hair cells.

Distortion-product and click-evoked otoacoustic emissions in healthy newborns.

Distortion-product otoacoustic emissions (DPOEs) are believed to provide frequency-specific information about cochlear function. The DPOEs have been reported in the adult population but have not been reported previously in the neonatal population. We recorded DPOEs from a group of healthy full-term newborn human subjects (35 ears) to establish the characteristics of these emissions in the newborn population. To our knowledge, this is the first study of DPOEs in newborns. The "DPOE audiograms" from the newborns tested revealed characteristics qualitatively similar to those seen in adults with normal hearing. This study demonstrates the feasibility of DPOE measurements among newborns and provides a normal baseline for this age group, thus fulfilling a necessary step toward the development of an objective, noninvasive frequency-specific test of cochlear function. Click-evoked otoacoustic emissions were also recorded from the newborn population and compared with click-evoked otoacoustic emissions from adults. The spectrum of the click-evoked emissions was variable and individualistic, similar to findings previously reported in adult subjects. The click-evoked otoacoustic emissions of the newborns had a higher overall level and contained stronger high-frequency (4.5 to 6 kHz) spectral components than those of the adults. We also found that the low-frequency components of the click stimulus spectrum were attenuated in the neonatal ears exhibiting a high-pass slope below about 2.5 kHz, whereas the stimulus spectrum was nearly flat in this frequency region in adult ears.

Otoacoustic emissions in normal and hearing-impaired children and normal adults.

Although distortion-product otoacoustic emissions (DPOEs) have been studied in adults recently, there is little information regarding them in young children. DPOEs and click-evoked otoacoustic emissions (CEOEs) were measured from a same group of normal and hearing-impaired children (age 4 through 10 years) and normal adults (age 22 through 29 years). Measurements of DPOEs in 13 children's ears with normal hearing showed higher levels of emissions in the 700- to 1400-Hz and 5.7-kHz regions relative to the data obtained in 10 normal adult ears. The 22 ears of children with sensorineural hearing loss demonstrated agreement between pure-tone audiograms and "DPOE audiograms." Measurements of CEOEs revealed that the average level of emission in 15 normal-hearing children's ears was slightly lower than that previously obtained in newborns, but slightly higher than that of adults. In children, the CEOE spectral components in the 4- to 6-kHz region were lower than in newborns, but higher than in adults. These results support the view that the DPOEs and CEOEs comprise a valuable tool in assessment of cochlear function in subjects of all ages.

Distortion product otoacoustic emissions in normal and impaired adult ears.

Distortion product otoacoustic emissions (DPOEs) were recorded in a group of normally hearing subjects (29 ears) and a group of subjects whose conditions were diagnosed as sensorineural hearing loss (23 ears) to study any correlation that might exist between DPOE characteristics and hearing impairment of different configurations. Three different DPOE paradigms have been used to investigate the influence of different test parameters on the DPOE data for normal and hearing-impaired ears. All normally hearing ears demonstrated detectable DPOEs, provided that the primary tone level was above a certain value. Hearing-impaired ears produced substantially reduced DPOEs compared with normally hearing subjects when the primary frequencies f1 and f2 corresponded to the region of hearing loss. Our data also suggested that, in general, more than one f2/f1 ratio is needed to examine any particular frequency region. The DPOEs provide frequency-specific information about cochlear function, which after further development, may form a basis for a noninvasive, objective method of evaluating cochlear function.

Auditory discrimination of tone-pulse onsets.

Two experiments are reported in which difference limens (DLs) were measured for onset times of a 1000-Hz tone pulse. An adaptive two-alternative forced-choice procedure and (mostly) well-trained subjects were used. In the first experiment, DLs were measured for the rise time of linear onset ramps at rise-time values between 10 and 60 msec. The DLs follow Weber's law up to a rise time of about 50 msec, and do not support the notion that rise times are perceived in a categorical manner. In the second experiment, DLs were obtained for linear, exponential, and raised-cosine onset envelopes at rise-time values between 10 and 40 msec. When energy differences in the critical band around 1000 Hz are computed for just-discriminable onsets, values between 0.7 dB (10-msec rise time) and 0.3 dB (40-sec rise time) are found. These equivalent intensity DLs show the same "near miss to Weber's law" behavior as do intensity DLs for pure tones.