1,720,971 research outputs found
An investigation into the relationship between input-output nonlinearities and rate-induced nonlinearities of click-evoked otoacoustic emissions recorded using maximum length sequences.
No full textThe maximum length sequence (MLS) technique allows otoacoustic emissions (OAEs) to be recorded using clicks presented at very high presentation rates. It has previously been found that increasing the click presentation rate leads to increasing suppression (termed "rate-suppression") of the MLS evoked OAE (Hine, J.E., Thornton, A.R.D., 1997. Transient evoked otoacoustic emissions recorded using maximum length sequences as a function of stimulus rate and level. Ear Hear. 18, 121-128). It has been suggested that the source of rate-suppression arises from the same nonlinear processes that give rise to the well-known nonlinear growth of OAEs. Based on this assumption, a simple model of rate-suppression (Kapadia, S., Lutman, M.E., 2001. Static input-output nonlinearity as the source of nonlinear effects in maximum length sequence click-evoked OAEs. Br. J. Audiol. 35, 103-112) predicts that both input-output (I/O) nonlinearity and rate-suppression can be unified by characterising the stimulus in terms of its acoustic power which, at high rates, is proportional to the click presentation rate. The objective of this study was to test this simple model by recording MLS OAEs from a group of normally hearing adults over a range of stimulus rates from 40 to 5000 clicks/s, and of stimulus levels from 45 to 70 dB peSPL. The results are broadly in agreement with the predictions from the model, though there appears to be some tendency for the model to slightly overestimate the degree of rate-suppression for a given degree of I/O nonlinearity. It is also suggested that the model may break down more significantly in the presence of spontaneous OAEs
Effect of subject task on contralateral suppression of click evoked otoacoustic emissions
No full textContralateral suppression of click evoked otoacoustic emissions (CEOAEs) is widely used as a non-invasive measure of the activity of the (uncrossed) medial olivocochlear bundle (MOCB). There is evidence that the uMOCB receives descending input from the cortex, potentially mediating top-down control during higher order processing. This study investigated whether the contralateral suppression measure is affected by top-down influences during different tasks performed by the participants during recording. Suppression of CEOAEs evoked at 50 and 60 dB SPL was measured under four different task conditions: (1) no task; (2) passive visual (watching a silent subtitled DVD); (3) active visual (responding to visually presented sums); (4) active auditory (detecting tone pips embedded in the evoking click train). The most significant effect of task was found on the recording noise, with both the passive visual and the active auditory task producing significantly lower noise levels than the no task condition. In the passive visual task, this was associated with a reduced inter-subject variability, which enhanced the effect size relative to the no task condition. A main effect of subject task was also found on the change in CEOAE I/O slope due to contralateral noise. This effect reflected a significantly smaller suppression during the active auditory task compared to the no task condition, leading to a reduced effect size. No significant difference in suppression strength between the no task condition and the two non-auditory tasks was observed, suggesting that the main effect of task reflects a specific effect of auditory attention. The data suggest that MOCB activity is inhibited due to top-down influences when selective attention is focussed on the ipsilateral ear
Volterra Slice otoacoustic emissions recorded using maximum length sequences from patients with sensorineural hearing loss
No full textWhen normally hearing ears are stimulated with maximum length sequences (MLS) of clicks, a family of non-linear temporal interaction components of otoacoustic emissions (OAEs) can be derived, which have been named Volterra Slice OAEs (VS OAEs). This study investigates the sensitivity of VS OAEs to sensorineural hearing impairment in adults, compared to that of the widely used derived non-linear click evoked OAE (DNL CEOAE). VS OAEs and DNL CEOAEs were obtained from 24 normally hearing and 24 hearing impaired ears using a custom-built MLS system and a Otodynamics 'IL088' OAE Analyzer, respectively. The results show that, based on waveform reproducibility, VS OAEs are as successful as DNL CEOAEs at separating normal from impaired ears at the audiometric frequencies of 1 and 2 kHz, where a strong correlation is found between the amplitudes of the two OAE types. At 4 kHz however, VS OAEs are a significantly better indicator of hearing loss than DNL CEOAEs. This difference at 4 kHz appears to be due to the lack of stimulus artefact contamination of VS OAEs in the early, high frequency portion of the response. The findings suggest that VS OAEs may provide a better diagnostic and monitoring tool for hearing loss at high frequencies than the conventional DNL CEOAE
Properties of volterra slices of otoacoustic emissions in normal-hearing humans obtained by using maximum length sequences of clicks
No full textNonlinear temporal interaction components of otoacoustic emissions (OAEs) may be investigated by presenting a stream of clicks in maximum length sequences. This yields responses, termed here Volterra slices, which are related to the Volterra kernels of the system. The aim of this study was to obtain normative data on Volterra slices over a range of click rates and stimulus levels. OAEs were recorded in 12 normally hearing adult ears at six rates and four click levels. In addition to the first order kernel, six slices from the Volterra slices of orders 2–5 were extracted from the recordings. It was found that higher order kernel slices could be reliably measured in all 12 ears tested and that they have properties that differ from those of the conventional OAEs. These findings may facilitate the study of cochlear function in both normal and pathological ears
Reducing stimulus artefacts in transient evoked otoacoustic emission measurements by using maximum length sequences
No full textSelective attention increases the temporal precision of the auditory N-100 event-related potential
No full textSelective attention increases the amplitude of the averaged N-100 event-related potential (ERP). This increase may result from more neurons responding to the stimulus or from the same number of neurons better synchronised with the stimulus, or both. We investigated the synchronization mechanism using a new response latency jitter measurement algorithm that performed well for all the signal-to-noise ratios obtained in the experiment. We found that the significantly increased N100 amplitude is accounted for by a significantly decreased latency jitter variance for the attended stimuli
Effects of maturation on parameters used for pass/fail criteria in neonatal hearing screening programmes using evoked otoacoustic emissions
No full textWe aimed to investigate the incidence of false alarms that occurred with the pass/fail criteria used in a published series of neonatal hearing screening programmes, as a function of age. We analysed the database of 19137 normally hearing babies (38274 ears) tested in the Wessex Universal Neonatal Hearing Screening Project. Otoacoustic emissions were recorded prior to discharge from maternity units, using IL088 equipment. We assessed the pass/fail rate using the Wessex criteria and 10 other pass/fail criteria published in the literature. Using Pearson's correlation coefficient, a statistically significant correlation between signal-to-noise ratio at each of the frequency bands 1, 2, 3, 4 and 5 kHz and babies' age in hours at the 0.01 level was identified. The correlation was also significant (0.01 level) between age and frequency reproducibility in each of the bands at 1, 2, 3, 4 and 5 kHz as well as the whole reproducibility. The number of false alarms reduced significantly after the first 24 h of life with all the criteria examined. We conclude that in the first hours after birth due to insufficient maturation of the otoacoustic emission, there is a high rate of false alarms. This increase in the false alarm rate, whilst dependent on the criteria used, occurs with all criteria. This leads to the consideration of whether the establishment of age-dependent pass/fail criteria could reduce the false alarm rate and the subsequent strain on diagnostic centres. Copyright (c) 2007 S. Karger AG, Base
Auditory brainstem response findings in hypothyroid and hyperthyroid disease
No full textObjective: Retrocochlear sensorineural hearing loss, associated with hypothyroidism, has been reported. This study investigated that claim. Methods: Audiometric and auditory brainstem response (ABR) measures of patients with hyper- and hypothyroidism. Results: The hyperthyroid group (14 patients) gave no audiometric or ABR results that differed significantly from normal controls. The audiometric findings for the hypothyroid group (21 patients) showed that 36% of this group had a four frequency average threshold greater than 25 dB. The statistically significant findings for ABR were a reduction in the amplitude of waves III and V and an abnormal increase in the I-V interval, appearing to confirm a retrocochlear disorder. However, as these patients have a low body temperature, the data were analysed by temperature and the results showed that the ABR abnormalities could be explained by body temperature. Conclusions: Hyperthyroid patients did not differ significantly from the controls. The four frequency average threshold and ABR results in hypothyroid patients did differ from the controls. However there is no clear evidence that the retrocochlear involvement is a direct result of the hypothyroidism. The abnormalities in the ABR can be explained by the low body temperature seen in these patients. Significance: This corrects the impression that hypothyroid patients have retrocochlear problems (indicated by ABR); a conclusion confirmed by data from 7 patients after thyroxin treatment when body temperatures. were close to normal values and ABR I-V intervals within or near normal limits
False positives in universal neonatal screening for permanent childhood hearing impairment
No full textHigh rates of false-positive neonatal screens for permanent childhood hearing impairment (PCHI) associated with raised hearing thresholds lead to unnecessary assessments of the baby, which may worry parents. False-positive rates need to be reduced, especially in view of the UK government's announcement that national neonatal screening will be introduced. We report screening criteria that give a six-fold reduction in false-positive rates.We have reported a trial in the Wessex region of the UK, which showed that universal neonatal screening for early identification of permanent childhood hearing impairment (PCHI) is highly effective.1 Universal neonatal screening increased the yield before 6 months of age of true cases of bilateral moderate or severe PCHI by 71 per 100?000; the equivalent to four of five cases expected in the target population for screening. We have not previously reported the false-positive rate, which is the rate of screening positive in babies not affected by the target condition.If a baby screens positive for hearing impairment (HI), follow-up tests are needed, including an estimation of hearing threshold and, if the threshold is raised, more tests and a medical assessment to find out whether or not the hearing loss is permanent. The cost of a postneonatal screening follow-up in one of the centres in the Wessex trial was £5540 per 1000 patients in the target population each year.2 This did not include the costs to the parents such as any increase in anxiety.We report the yield of true cases, positive predictive value, false-alarm rate, and raised hearing threshold rate in 158 babies who screened positive from 12?523 babies screened during the second half of the Wessex trial. We also report, in the same population, the effect of increasing the threshold for screening positive and compare these figures with data from Whipps Cross Hospital, London, UK,3 a study of transient evoked otoacoustic emissions (TEOAE)-based universal neonatal screening in the UK.We used a two-step neonatal screen.1 First we tested for TEOAE. In infants younger than 48 h, a pass on the first step was defined as unilateral detection of TEOAE although in older babies, bilateral detection was required. Babies failing the first step proceeded, on the same day, to the second step of automated auditory-brainstem-response (AABR) testing. A positive screen was defined as unilateral failure on AABR (table 1). In the amended protocol (table 1) a positive screen was redefined, in the subgroup of babies at low risk,1 as bilateral failure on AABR testing. The Whipps Cross hospital screen (table 1) used TEOAE testing as the first and second step before and after postnatal discharge from hospital, respectively, with bilateral failure on the second occasion constituting a positive screen.<br/
Nonlinear properties of otoacoustic emissions in normal and impaired hearing
No full textClick-evoked otoacoustic emissions (CEOAEs) exhibit nonlinearities in amplitude and time domains. The first objective of this study was to investigate whether there is any correlation between the temporal and amplitude nonlinearities of CEOAEs in normals. Additionally there is evidence that pathology affects the normal cochlear nonlinearity. The second objective was to investigate whether pathology affects the temporal nonlinear components.Conventional and maximum length sequence (MLS) CEOAEs were recorded in normal subjects and in patients with mild hearing loss. The slope of the input–output (I/O) function of the conventional CEOAE measured the amplitude nonlinearity. Two measures of temporal nonlinearity were the magnitude of the suppression that occurs with increase in stimulus rate and the amplitudes of the second and third order temporal interaction components (Volterra slices).The amplitude nonlinearity is well correlated with both the magnitude of the rate suppression and the amplitudes of the Volterra slices. The ‘linear’ CEOAE amplitude showed no differences between the normal and patient groups but the differences in the Volterra slices were substantial. This suggests that the first sign of damage to the cochlea is that the system becomes more linear. Hence the Volterra slices may provide a sensitive measure of cochlear damage
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