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What is the difference between a conduction hearing loss and nerve deafness,how common is hearing loss in infants treatment,chronic fatigue syndrome pdf - PDF Review

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The basic battery of audiometric tests normally includes pure-tone testing of threshold by both air and bone conduction, speech reception threshold (SRT), and speech discrimination (SDS). Objective 3: Thus, the shape of the bone conduction audiogram is a measure of the sensitivity of the inner ear alone, while the difference between air conduction and bone conduction is a measure of the degree of hearing loss attributed to the middle ear. Speech discrimination, as opposed to speech sensitivity, is the person's ability to not only hear words but to identify them.
Individuals suffering only a conductive hearing loss will be able to identify words if the sound is loud enough. Infants respond to sounds in the free field or through earphones with facial responses (grimaces, smiles, brow raising) or with head turning.
By 24 months of age other test strategies can be used based on the child's natural curiosity about objects in the environment. Testing may also be objective in the sense that it is not required that the subject consciously respond to the sound.
This method assesses the mobility or compliance of the tympanic membrane and thereby provides important information about the function of the middle ear including the tympanic membrane, ossicles, and Eustachian tube.
Cochlear and auditory nerve electrical activity can be recorded from human patients from electrodes advanced through the tympanic membrane and placed on the otic capsule. A silver disc electrodes taped to the skull record the electrical activity of the brain (EEG). The time period most commonly studied covers the first 12 msec after the stimulus is presented to the ear and, hence, represents the electrical activity evoked in neurons in the auditory nerve and brainstem.
Traditionally, persons with a hearing loss have been fitted with a hearing aid, a device that simply amplifies the sound. For treating profound sensorineural hearing loss, a cochlear prosthesis has been developed to aid those individuals with little or no residual hearing. Key words: auditory, hearing aid, hearing loss, learning, masking noise, nonsense syllables, perception, perceptual training, personal computer, phonemes, presbycusis, rehabilitation, speech. Abbreviations: CV = consonant-vowel, DT = delayed training, HA = hearing aid, IT = immediate training, NS = nonsignificant, NST = nonsense syllable test, PC = personal computer, R-SPIN = Revised Speech Perception in Noise (test), SNHL = sensorineural hearing loss, SNR = signal-to-noise ratio, SPL = sound pressure level, VA = Department of Veterans Affairs, VC = vowel-consonant.
Progressive high-frequency sensorineural hearing loss (SNHL) alters auditory processing at multiple levels of the auditory system.
While hearing aids (HAs) can partially compensate for cochlear deficits by amplifying high-frequency sounds, long-standing peripheral hearing loss will also produce neuroplastic alterations within the central auditory system, including changes in synaptic connections and dendritic arborization [7]. Research over the last decade has revealed extensive neuroplasticity in the auditory system that optimizes neuronal responses to the behaviorally relevant acoustic features present in the environment [16-18]. Since synaptic connections within the central nervous system are in continuous flux, neuronal reorganization that has occurred as a consequence of gradual hearing loss will continue to impair hearing even if normal cochlear function were completely restored by an HA.
Perceptual learning can be optimized with adaptive training paradigms that are targeted to enhance selected sensory discriminations. Recently, Sweetow and Palmer reviewed the capability of perceptual training to improve hearing in patients with SNHL [41]. Stimuli for both at-home training and in-laboratory testing consisted of 27 consonant-vowel (CV) and 27 vowel-consonant (VC) syllables selected from the NST. During the NST, stimuli were mixed with speech-spectrum noise at 10 and 0 dB signal-to-noise ratios (SNRs). Laboratory testing was performed in 8 ? 8 ft single-walled, sound-attenuating testing rooms. A preconfigured multimedia PC was installed in a quiet location of each subject's home.
The stimuli were identical to those used in laboratory testing, with the exception that only two voices (one female and one male, counterbalanced across subjects) were used for training. Eight experienced HA users (mean HA experience = 16 months, range 10-21 months) were recruited from a group of subjects who had participated in a previous study that evaluated acclimatization with 9- and 16-channel HAs with wide dynamic range compression [26]. Training and testing procedures were identical to those used in Experiment 1, except that a different set of measurements was obtained before the HA experience.
Figure 3 shows the changes of NST scores relative to the initial performance measured after HA fitting (week 0). Small performance improvements were seen in NST scores in the absence of training (Figure 3). Figure 4 plots improvement in NST scores over time for stimuli presented at 0 and 10 dB SNR. Differences between improvements due to amplification and training appeared to reflect the difficulty of phoneme discrimination. An important issue in assessing the efficacy of perceptual training is the extent to which training-related improvements generalize to items that were not specifically trained. The critical question was, Would subjects who had extensive experience with their HAs and with the NST procedures show further benefit from adaptive training?
The current experiments demonstrate daily focused training in adaptive phoneme identification produces substantial benefits in syllable discrimination for HA users-a benefit that significantly exceeded the initial benefit of amplification. Each subject who underwent training in either Experiment 1 or 2 showed some improvement in NST scores. Subjects showed continued improvement over the entire 8-week duration of training (Figure 3), with performance improving most rapidly at training onset followed by an additional improvement of approximately 2 percent for each doubling of training duration between 1 and 8 weeks. With respect to the time between HA fitting and rehabilitative training, the current results showed NS differences between immediate training and training delayed by 8 weeks. Research on perceptual learning has identified two major components of the improvement in performance seen with adaptive training: procedural learning and perceptual learning [43].
As in other studies of perceptual training, we expected the results of the current study to include contributions from both procedural and perceptual learning.
Although studies of perceptual learning have emphasized the power of focused training, alterations of the sensory environment can also drive cortical reorganization [20-21,59]. Improvement in the discrimination of isolated syllables correlates with the improved discrimination of the same syllables in sentence contexts [61].
The evaluation of generalization of training effects to improvement in sentence processing was not originally planned. The results of this study demonstrate that phoneme recognition by HA users can be significantly enhanced through focused perceptual training. Although the improvement from both HA fitting and perceptual training was substantial, benefits appear to reflect complementary processes. This material was based on work supported by the VA Rehabilitation Research and Development Service, grant C2975C. In Experiment 1, new HA users were randomly assigned to either immediate training (IT) or delayed training (DT) groups.
Most obviously, it alters cochlear function and deprives listeners of high-frequency speech cues that are critical in discriminating consonants [1]. While the newly amplified auditory inputs provided by HAs may enhance functional neuroplasticity [8], abnormal synaptic connections will not instantly renormalize. Changes in cortical organization occur reliably following both selective stimulation and deprivation.
In cats with high-frequency hearing loss, neurons in auditory cortex originally tuned to high frequencies alter their tuning to process inputs from intact nearby portions of the cochlea [2,22]. With typical SNHL, high-frequency inputs are gradually lost, altering the acoustic cues accessible to phonetic analysis. A wide array of recent research has demonstrated that perceptual learning paradigms can drive neuronal reorganization in visual [27-29] and auditory [30-31] modalities. Existing rehabilitation training usually consists of group discussions that include other HA users and their families [39]. Several studies of adaptive auditory training have shown performance improvements in subjects with hearing loss [42-43], particularly when visual cues are present [44]. Twenty-three subjects (all male) with mild-to-moderate SNHL were recruited from the Department of Veterans Affairs (VA) Audiology Service (Northern California Health Care System, Martinez, California). Both groups were first familiarized with the nonsense syllable test (NST) [1], and then we tested them in two separate sessions before HA fitting to measure unaided performance. They included a Creative Labs SB0240 sound card (Singapore) and a pair of Boston Acoustics satellite speakers (Model BA745) (Peabody, Massachusetts) positioned approximately 2 feet in front and 20° to the left and right of the listener's position. The interior walls of the rooms were covered by 1-inch acoustic foam, with ambient third-octave noise levels less than 20 dB SPL from 250 to 4000 Hz. The subject selected a comfortable chair to be used in training, and the position of the chair, table, and equipment on the table were marked to assure consistent stimulus delivery. These difference scores increased sensitivity to training and acclimatization effects with the removal of the considerable between-subject variation in test and training score performance. As part of that study, these subjects had participated in more than 60 hours of in-laboratory NSTs with two of the four voices used in the present study. The improvement due to the amplification is reflected in the difference between unaided and week 0 scores. If mere experience with the NST was a critical factor, subjects in Experiment 2 might be expected to show limited improvement because their previous experience with the NST (>60 h) exceeded the training plus laboratory testing experience of the trained subjects in Experiment 1. The results suggests that (1) chronic alterations of speech-cue use play a major role in the speech-processing deficits exhibited by sufferers of hearing loss and (2) focused adaptive training is an effective rehabilitation strategy that can significantly enhance NST scores beyond benefits obtained with HA use alone. Thus, increasing the duration of training from 8 to 16 weeks would be expected to result in another 2 percent improvement in performance. Training was also effective in the small group of experienced HA users studied in Experiment 2. Procedural learning involves increasing familiarity with the task and particular stimuli used in testing. Rapid procedural learning appeared to contribute to the early performance increases of 2 to 3 percent that were seen in the control group (Figure 3).
Thus, some degree of reorganization and perceptual learning might be expected to result from the amplification of high-frequency sounds because of new HAs, even without explicit training. Results of the current study were limited to demonstrating that benefits of phoneme-recognition training on one set of voices generalized to improved recognition of syllables spoken by untrained voices.


The benefit of such training in difficult listening situations exceeds the benefit provided by HAs only, generalizes to untrained voices, and persists for at least 8 weeks (the longest period over which we assessed performance). Our analyses of performance on stimuli differing in difficulty or presented at different SNRs indicate that HAs provided the most benefit for easily discriminable phonemes presented near threshold, while training provided more benefit for difficult discriminations in more audible speech. IT subjects underwent 8 weeks of at-home syllable identification training and in-laboratory testing, whereas DT subjects underwent identical in-laboratory testing without training. In addition, gradual high-frequency SNHL results in a widespread reorganization of central auditory connections, diminishing high-frequency inputs and enhancing connections from nearby zones with intact cochlear function [2]. Normalization may be reflected in the gradual perceptual changes occurring during acclimatization [9-11]. For example, explicit exposure to particular sound frequencies can enhance the number of cortical neurons driven by those stimuli and alter neuronal tuning properties and response latencies to favor behaviorally relevant sounds [19].
Perceptual learning results in cortical reorganization [16-17] that is reflected in altered response properties of single neurons [19] as well as large-scale alterations seen with functional magnetic resonance imaging [32] and event-related brain potentials [33-36].
While this training helps patients adjust their behavior for successful HA use [40], it is not designed to enhance their low-level perceptual use of the speech cues that the HA has restored. However, these studies typically required the intervention of a suitably trained clinician, which limited their practical application. The subjects ranged in age from 50 to 80 (mean = 69), had no history of neurological or psychiatric disorder, and were in good health.
Subjects who had HAs with volume controls were instructed to set the gain to a comfortable level and to not change the settings throughout training and testing.
Noise samples were 1,200 ms in duration, starting 200 to 290 ms before the onset of each syllable and extending beyond its offset. Subjects performed a phoneme identification task using a one-interval nine-alternative identification procedure. Additional components needed for PC installation (power strips, computer table, etc.) were provided when necessary. Also, the use of simple subtraction to track performance appears to be reasonable because all subjects performed well below ceiling on the majority of test and training item types.
Recruitment criteria, including audiometric configurations and etiology of hearing loss, were identical to those criteria used in Experiment 1.
The effects of acclimatization to the HAs and the test procedures in the absence of training can be seen in weeks 1 to 8 for the DT control group (dashed line). A regression analysis for weeks 1 to 8 showed a nonsignificant (NS) negative performance slope during this time, indicating that virtually all the improvement occurred during the first week. Although the small difference between IT and DT training effects (1.8%) did not reach significance, it was similar to the gains observed during the acclimatization period that would have been expected to contribute to IT training effects. Figure 7 plots performance improvement in NST scores with the black line showing performance on the trained voices and gray lines plotting performance for the untrained voices only heard during in-laboratory testing.
Although differences in subject groups and pretraining experience complicate direct comparisons of the magnitude of training effects in Experiment 1 and Experiment 2, clearly, perceptual training was highly effective in all HA users regardless of HA experience. Procedural learning occurs rapidly, but the improvement does not generalize effectively to different tasks [57].
These changes likely reflected increasing familiarity with the NST following the extensive testing (6 h) that occurred at the beginning of the control period. Some controversy exists regarding the extent to which new HA users show such acclimatization. This generalization suggests that subjects are not primarily learning specific acoustic features of a particular stimulus set but rather the abstract features that define phonetic categories across talkers. Nevertheless, higher-order processing operations depend on the extraction of syllables from the acoustical signal based on the analysis of the acoustic features that make up each utterance.
The improvement may have been limited by the fact that only a small portion of the phonemes appearing in the target words of the R-SPIN test had been used in perceptual training. We found that immediate and delayed training produced similar benefits, and we also found benefits in experienced HA users. These benefits were most pronounced for HA users with poor speech discrimination abilities. Plastic changes in the central auditory system after hearing loss, restoration of function, and during learning. Time-varying features of initial stop consonants in auditory running spectra: A first report. Perceptual cues to the voiced-voiceless distinction of final fricatives for listeners with impaired or with normal hearing. Enriched rehabilitative training promotes improved forelimb motor function and enhanced dendritic growth after focal ischemic injury. Physiological plasticity in the auditory system and its possible relevance to hearing aid use, deprivation effects, and acclimatization.
The time course and magnitude of perceptual acclimatization to frequency responses: Evidence from monaural fitting of hearing aids. Role of perceptual acclimatization in the selection of frequency responses for hearing aids. Plasticity in the frequency representation of primary auditory cortex following discrimination training in adult owl monkeys. Environmental enrichment improves response strength, threshold, selectivity, and latency of auditory cortex neurons. Loudness perception and frequency discrimination in subjects with steeply sloping hearing loss: Possible correlates of neural plasticity.
Magnetoencephalographic studies of functional organization and plasticity of the human auditory cortex. Enriched acoustic environment after noise trauma reduces hearing loss and prevents cortical map reorganization. Acclimatization in wide dynamic range multichannel compression and linear amplification hearing aids. Where practice makes perfect in texture discrimination: Evidence for primary visual cortex plasticity.
Learning-induced neural plasticity associated with improved identification performance after training of a difficult second-language phonetic contrast. Central auditory system plasticity: Generalization to novel stimuli following listening training. The time course of auditory perceptual learning: Neurophysiological changes during speech-sound training.
A cost-utility analysis of adult group audiologic rehabilitation: Are the benefits worth the cost?
Training produced large improvements in syllable identification in IT subjects, whereas spontaneous improvement was minimal in DT subjects. Phoneme processing strategies are correspondingly altered, with hearing-impaired subjects depending more on phonetic cues conveyed by low frequencies [3-6]. However, acclimatization effects are generally small in magnitude and inconsistently obtained [12-15]. Environmental enrichment can also sharpen neuronal tuning curves in auditory cortex [20], while noisy environments impair the development of normal tuning [21]. Some of these changes occur in auditory cortex and can be imaged electrophysiologically [24].
One would think that restoring speech cues with an HA would be sufficient to reestablish normal connections during acclimatization.
Here, we test the capability of focused perceptual training to enhance syllable discrimination in new and experienced HA users. In contrast, at-home personal computer (PC)-based perceptual training has received much recent attention as a possible treatment for central auditory processing disorder and dyslexia [45-50]. We used the difference between the initial aided and unaided scores to quantify the immediate benefit of hearing amplification. To incorporate natural speech variability, each speaker recorded six exemplars of each of the 54 syllables. At the start of each trial, nine syllables were displayed on a liquid crystal display monitor. A PC modem was connected (through a splitter) to the subject's telephone line for daily uploading of training results to a laboratory computer.
Six blocks of 108 trials each (one per list) were completed on each training day, followed by two additional blocks that presented stimuli from all lists in random order.
We analyzed data significance primarily with multifactorial analysis of variance but also used multifactorial regression and correlational analyses where appropriate. The effects of the training (solid lines) are seen in weeks 1 to 8 for the IT group and weeks 9 to 16 for the DT group.
The fact that the IT and DT effects did not differ significantly suggests that training need not be delivered immediately after HA fitting to be effective.
Greater improvement for more audible stimuli is consistent with the view that perceptual training enables HA users to improve the perception of speech cues made audible at the higher SNR.
The optimal duration of training would thus appear to depend on subject motivation and speech discrimination requirements. In addition, procedural learning is associated with learning arbitrary procedures of the training task and shows rapid reductions in performance once practice on the task ceases [19,43].
Procedural learning of 2 to 3 percent during the first week would be consistent with our previous findings of procedural learning effects during repeated NSTs [26].
Some studies suggest a very rapid adjustment of speech perception (with a time course similar to that of procedural learning) with performance asymptoting soon after the receipt of a new HA [12-13,60]. Indeed, evidence from older subjects suggests that syllable discrimination skills correlate directly with verbal memory performance when cognitive factors are controlled [63-64]. The R-SPIN test requires the subject to listen to sentences in a background of competing multitalker babble and repeat the final word of each sentence.
Because we scored only low context sentences, scores would have been minimally influenced by improvements in context provided by improved perception of trained phonemes in other portions of the sentence.


Further study is needed to define the optimal parameters of training, but our results suggest that training can benefit all HA users, including those who have been wearing HAs for years.
This finding suggests a complementary role in which HAs bring acoustic information above threshold and therefore make it accessible to the hearing impaired individual, whereas training facilitates the optimal use of that information, particularly for HA users who have difficulty processing speech.
DT subjects then underwent training and showed performance improvements comparable with those of the IT group. This minimal acclimatization benefit suggests that the neuroplastic changes needed to normalize auditory perception often may not occur.
The magnitude of auditory cortex reorganization following hearing loss depends critically on the nature of the posttraumatic acoustic experience. However, acclimatization effects for most types of HAs are small in magnitude and difficult to distinguish from improvement due to increased familiarity with test materials [26]. Although the mechanism by which PC-based training enhances performance in these disorders is not well understood [51], training effects can be substantial.
They were randomly assigned to one of two conditions: 12 subjects were assigned to the immediate training (IT) group and received training during the initial 8 weeks of HA use after a 1-week acclimatization period.
Postfitting performance scores also provided the baseline against which training-related changes (IT group) and acclimatization (DT group) were assessed. Syllables were selected randomly from among different exemplars during both training and testing. We jittered syllable onset by ±45 ms on each trial to reduce the predictability of syllable timing with respect to noise onset.
The response choices included all possible consonants paired with the vowel that had been presented. Instruction in PC use was also provided when necessary: 29 percent of the patients had not used PCs before and 32 percent had only minimal familiarity. Depending on response speed, daily training duration ranged from approximately 35 to 70 minutes.
In all cases, the large amount of data from the NST and training paradigm permitted us to average together sufficient numbers of binary responses so that resulting distributions had approximate Gaussian error distributions.
Perceptual learning, on the other hand, involves increasing sensitivity to task-relevant distinctions in the stimuli themselves and is thought to reflect a reorganization of the neural representations that underlie discrimination and recognition. Most likely, procedural learning effects occur in parallel with perceptual learning and thus would have also contributed to the rapid improvements seen in the IT group during the first several weeks of training.
Other studies suggest that speech perception continues to improve for months after an HA fitting [9-11]. This finding supports the notion that perceptual success of HA users comes at the cost of the extra effort that is needed for analyzing phonemes and might otherwise be available for analyzing sentence content. It consists of eight lists of 50 sentences each, divided into equal numbers of high- and low-context sentences. Further study with more sensitive tests is needed to evaluate the impact of syllable identification training on sentence processing. Training-related improvement in NST scores significantly exceeded improvements due to amplification. In the current study, we investigated the capability of adaptive perceptual training to force reorganization and consequent perceptual improvement in a high-level auditory task: syllable identification. For example, recent evidence suggests that the reorganization of the tonotopic map of primary auditory cortex following sudden high-frequency hearing loss can be reduced by exposure to an auditorily enriched environment with an overrepresentation of high-intensity sounds at frequencies in the expected range of hearing loss [25]. In this study, we evaluated the effect of at-home PC-based auditory training on the syllable identification capabilities of patients with SNHL who were new (Experiment 1) or experienced (Experiment 2) HA users. The remaining 11 subjects were assigned to the delayed training (DT) group as untrained controls during the first 8 weeks of testing and then received training during the subsequent 8 weeks.
HAs were fitted using the NAL-NL1 (National Acoustic Laboratories' nonlinear fitting procedure, version 1 [Australia]) target [52] and verified by probe microphone measurements. Two voices, one female and one male, were selected for training of each subject, with the selected voices counterbalanced over subjects.
Once training was completed, the PC automatically connected to the Internet with Windows scripting tools and the training data was uploaded to the laboratory computer.
Together with the effects of SNR, these results suggest that amplification improved performance on easily discriminated speech sounds occurring near threshold, while training improved the discrimination of difficult consonants distinguished by high-frequency speech cues.
Thus, training appeared to be particularly effective in subjects who had disproportionate impairments in syllable discrimination compared with their audiograms.
Of course, in the current experiments, we trained only a small proportion of English CVs and VCs.
Work in our laboratory supports long-term acclimatization, but only for certain types of HA [26]. The implication is that improved syllable discrimination would result in not only improved syllable recognition but also improved sentence comprehension and memory.
The high-context sentences are used primarily in evaluating the cognitive abilities of subjects. Recently, more complex adaptive training sequences have shown efficacy in improving sentence test scores [66].
In Experiment 2, experienced HA users received identical training and testing procedures as users in Experiment 1. First, many HAs do not present consistent high-frequency speech cues across a broad range of speech intensities, thus complicating the perceptual learning process.
The DT group received no training during the initial 8-week period and served as controls for the IT group. We examined generalization by testing performance with all four voices (both trained and untrained). We monitored uploaded data daily to assure that the training of each subject was proceeding according to schedule.
As with the subjects tested in Experiment 1, retention testing 8 weeks after training ended showed no performance decrement.
Most subjects completed 35 to 40 days of training, and no correlation was found between the minor variation in the number of days of at-home training and the magnitude in-laboratory NST improvement.
The duration of perceptual learning appears to increase with the complexity of the training material [56].
In the current study, the performance of control subjects increased rapidly and then declined slightly from weeks 2 to 8.
We scored only the low-context sentences in which the final word is minimally constrained by the content of the sentence.
An individual may hear a sound well enough, but the neural signals may be altered to the extent that the sound is unintelligible.
Thus, training benefits may be more substantial and increases may continue for longer training periods with more complex phonetic material.
An intriguing possibility is that such acclimatization failures reflect the inadequacy of perceptual learning during everyday conversations. To limit item repetition, we tested with subsets of three lists (a total of 75 low-context sentences) per test. Training-related improvements generalized to untrained voices and were maintained on retention tests.
Visual, semantic, and redundant low-frequency phonetic cues often allow one to understand information without relying on normal high-frequency phonetic cues.
Following the delay period, subjects in the DT group underwent an identical training regimen.1 For the DT group, week 8 scores were used both as end point measures of acclimatization and as baseline measures for evaluating training effects. Each session of laboratory testing consisted of four blocks of 324 randomized trials (3 trials of each syllable at each SNR). Limited learning would be expected under these conditions because the majority of syllables are either too easy (in which case no errors are made) or too difficult (in which case the stimulus may not be heard at all) and performance feedback is variable and inconsistent.
Before data collection, we tested each subject using sentences from two of the R-SPIN lists, with individual sentences presented at 8, 12, 16, and 20 dB SNR. Perceptual training appears to be a promising tool for improving speech perception in new and experienced HA users.
Indeed, impaired individuals may try to avoid difficult high-noise situations where high-frequency cues become more essential. Both trained and untrained voices were tested with the talker's voice fixed for the duration of each block.
Trainees completed 29 to 44 days of training in the 8-week period, with the median 37 days and the mode 40 days of training.
These results are consistent with studies that reported that spontaneous perceptual learning is enhanced with multichannel HAs [26].
Moreover, with most HAs, the acoustic features that characterize syllables will vary with the intensity of the speaker's voice and be masked to varying degrees depending on background noise levels.
Subsequent R-SPIN testing was done at the SNR that produced performance nearest to 50 percent correct for each subject. Finally, feedback about phoneme-processing errors is delayed and inconsistent in normal conversation so that subjects lack the critical information needed for low-level perceptual changes to occur. Nonoverlapping sets of three R-SPIN lists were used for testing at weeks 0 and 8, while a third test at week 16 reused the lists from testing of week 0.
Each list provided a single score based on the percentage of low-context words repeated correctly. Each subject's score was computed as the mean of scores for the three lists on each test day.



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