The present study demonstrated that the prevalence of deafness in individuals with the A1555G mitochondrial mutation was likely to be high even in the absence of aminoglycoside exposure and clearly showed the association of severe to profound hearing loss with the onset of hearing loss before age 10 years.

ObjectivesSpeech perception abilities, which vary widely among cochlear implant (CI) users, are considered to be associated with the integrity of the central auditory pathways from the auditory nerve to the cortex. Therefore, auditory evoked potentials (AEPs) are used to evaluate central auditory processing, which is thought to contribute to speech perception in CI subjects. In AEPs, the P300 component reflects the cognitive ability of subjects to detect and respond to stimuli and has most frequently been used and investigated in CI subjects. Other studies have used mismatched negativity (MMN) to examine central auditory processing. It is important to compare MMN and P300 and examine the auditory processing mechanisms involved in these components. Our study therefore aimed to investigate the relationship between P300 and MMN using both active and passive hearing paradigms in CI and normal hearing (NH) subjects.MethodsOur subjects consisted of 3 CI subjects and 3 NH subjects. An oddball paradigm was used to deliver the stimuli on both components. The frequent stimuli were 1,000-Hz tone bursts, whereas the rare stimuli were 1,500, 2,000, and 4,000-Hz.ResultsAs the frequency contrasts increased, the P3 latencies increased in the CI subjects. However, the latency in NH subjects did not change significantly across the frequency contrast conditions. MMNs were identified for both the CI and NH subjects; the latencies in the CI subjects were longer than those in the NH subjects. However, there were no differences in the latencies of either the CI or NH subjects in the 3 frequency contrast tasks.ConclusionOur results indicated that different auditory processing pathways are involved in the active and passive hearing conditions based on the P300 and MMN data and that a combination of both responses plays an important role in the comprehension of auditory processing mechanisms in CI subjects.

To elucidate the pathophysiological and genetic mechanisms of hearing loss associated with the homoplasmic mitochondrial A1555G mutation in the absence of aminoglycoside exposure, we conducted audiological and genetic analyses on 67 maternally related members of a large Japanese family carrying this mutation. A consistent pattern was evident in the audiograms, with features of sensory presbycusis, cochlear origin at all levels of hearing loss, and a high degree of vulnerability of outer hair cells. That the degree of hearing loss was similar in affected subjects within the same sibling group but differed between sibling groups suggests the involvement of nuclear modifier genes. Total mitochondrial DNA sequences were completely identical among subjects with various levels of hearing loss, and lacked additional pathogenic mutations. For the diagnosis of sensorineural hearing loss, the mitochondrial A1555G mutation should be considered when these features are present even in the absence of aminoglycoside exposure.

In this study, we investigated the relation between the use of hearing aids at the initial stages of hearing loss and age-related changes in the auditory and cognitive abilities of elderly persons. 12 healthy elderly persons participated in an annual auditory and cognitive longitudinal examination for three years. According to their hearing level, they were divided into 3 subgroups - the normal hearing group, the hearing loss without hearing aids group, and the hearing loss with hearing aids group. All the subjects underwent 4 tests: pure-tone audiometry, syllable intelligibility test, dichotic listening test (DLT), and Wechsler Adult Intelligence Scale-Revised (WAIS-R) Short Forms. Comparison between the 3 groups revealed that the hearing loss without hearing aids group showed the lowest scores for the performance tasks, in contrast to the hearing level and intelligibility results. The other groups showed no significant difference in the WAIS-R subtests. This result indicates that prescription of a hearing aid during the early stages of hearing loss is related to the retention of cognitive abilities in such elderly people. However, there were no statistical significant correlations between the auditory and cognitive tasks.

A total of 1000 daily-used sentences were constructed by two clinical audiologists. These sentences consisted of 15 to 18 morae per sentence (counting CV or V phoneme as one mora or a syllable) that can be uttered in about two seconds at normal rate. Each sentence was controlled for length (15 to 18 morae, or syllables), for the syntactic structure (noun phrase'object' verb phrase), and for the phonemic distribution (about 22 different phonemes). They were presented in live voice and were judged by five adults for naturalness using a seven point scale (70natural, 1 0artificial). The 367 sentences that received mean ratings of six or seven were retained. Five other adult subjects then listened to the sentences at about 60 B SPL to judge the naturalness, and a total of 300 sentences remained for recording by a professional Japanese male voice actor. Other sentences judged as unnatural were excluded. Estimation of performance-intensity functionSentence intelligibility was measured at (5 dB or (7 dB S/N ratio, 20 sentences each, with noise fixed at 65 dBA, for 11 subjects with hearing thresholds 15 dBHL or better at the octave frequencies from 125 Hz to 8000 Hz. Results revealed that a 1-dB change in S/N ratio changes speech intelligibility by 8.9%. Equalization of sentence difficultyFor the additional nine normal-hearing young subjects, the percent intelligibility was measured at (5 dB and (7 dB S/N ratio, with noise fixed at 65 dBA, and the subjects were asked to repeat the exact sentence. The experiment was carried out twice. Average sentence scores of 76%90.16 SD for (7 dB were obtained, and 269 sentences remained after the deletion of 31 sentences: 15 sentences were 100% correct, six sentences were deleted after high-low analysis, and in 10 sentences the scaling was too large. Formation of sentence listsTwenty-four lists of 10 sentences each that were considered to have equal phonetic distribution were created at first, with a target of 20 different phonemes in a sentence. Those were then paired to yield 12 lists of 20 sentences, carefully counting the number of phonemes. There were 111.893.07 segmentations, grammatically correct units, per list. Each sentence contained an average of 22.7 different phonemes, in which 49.8% were vowels and 50.2% were consonants. Development of norms and reliabilityUsing the final test material, three sets of experiments were carried out in two centers (A, B): (1) performance intensity function on 25 subjects; (2) sound field norms on 85 subjects; and (3) headphone norms on 65 subjects. The subjects ranged between 16 to 37 years old (mean 022.5), and bilateral hearing thresholds were 15 dB HL or better at the octave frequencies of 125 to 8000 Hz. Variations in response that did not change the meaning of sentences were allowed, such as the verb ending form of the sentence.In relation to the subject's threshold, PI function measurement was carried out, fixing the SNR at '1.5, 0, (1.5, (3, (6, and (7.5 dB. The results revealed that speech intelligibility changes by about 8Á10% per de...