Brainstem Correlates of Comodulation Masking Release for Speech in Normal Hearing Adults

BACKGROUND AND OBJECTIVES: Weak signals embedded in fluctuating masker can be perceived more efficiently than similar signals embedded in unmodulated masker. This release from masking is known as comodulation masking release (CMR). In this paper, we investigate, neural correlates of CMR in the human auditory brainstem. SUBJECTS AND METHODS: A total of 26 normal hearing subjects aged 18-30 years participated in this study. First, the impact of CMR was quantified by a behavioral experiment. After that, the brainstem correlates of CMR was investigated by the auditory brainstem response to complex sounds (cABR) in comodulated (CM) and unmodulated (UM) masking conditions. RESULTS: The auditory brainstem responses are less susceptible to degradation in response to the speech syllable /da/ in the CM noise masker in comparison with the UM noise masker. In the CM noise masker, frequency-following response (FFR) and fundamental frequency (F0) were correlated with better behavioral CMR. Furthermore, the subcortical response timing of subjects with higher CMR was less affected by the CM noise masker, having higher stimulus-to-noise response correlations over the FFR range. CONCLUSIONS: The results of the present study revealed a significant link between brainstem auditory processes and CMR. The findings of the present study show that cABR provides objective information about the neural correlates of CMR for speech stimulus.

Effects of Age on Speech-in-Noise Identification: Subjective Ratings of Hearing Difficulties and Encoding of Fundamental Frequency in Older Adults

BACKGROUND AND OBJECTIVES: Numerous studies have indicated deterioration of speech perception in noisy conditions among the elderly even those with normal hearing capabilities. The aim of this study was to investigate the effects of age on the speech-in-noise identification by speech-in-noise (SIN) test, subjective ratings of hearing difficulties by speech, spatial, and qualities of hearing scale (SSQ) questionnaire and encoding of fundamental frequency (F0) by Speech auditory brainstem response (ABR) in the elderly and comparing the results with young people. SUBJECTS AND METHODS: The present study was conducted on 32 elderly people aged over 60 years old (17 male and 15 female) with the mean age of 68.9 (standard deviation=6.33) possessing normal peripheral hearing and 32 young subjects (16 male and 16 female) aged 18-25 years old. RESULTS: Findings showed that the score of SIN test is lower among the elderly people as compared with young people in signal-to-noise ratios of 0 and -10 based on Iranian version of SSQ questionnaire (p < 0.001). The range of F0 amplitude in the elderly people is also lower than young people (p < 0.001) in Speech ABR. CONCLUSIONS: It seems that speech processing in older people is deteriorated comparing with young people regardless of their normal peripheral auditory thresholds. This decrease will result in weaker perception and improper segregation of speech from other competing sources.

novel approach for extracting important cues in complex auditory brainstem response to /da/ using fuzzy model

Gathering an insight into brainstem task in generating auditory response to complex stimuli and its nonlinear behavior can be an important base in auditory system modelling, but no study has been done to demonstrate the nonlinear dynamic behavior of auditory systems considering cABR. This study attends the dynamic modeling of auditory brainstem response to consonant-vowel syllable /da/ using fuzzy logic as nonlinear mapping of the input and output of the system. We recorded cABR to /da/ from 40 normal Farsi speaking subjects in response to /da/ with 40ms duration. This data set was divided to train and validation sets. We implemented a fuzzy logic based model for the dynamic extraction of cABR to /da/ for data set. This model includes singltone fuzzifier, product inference engine and weighted center of average defuzzifier. Rule base representing dynamic of signal was generated and, then, firing rate of each rule was calculated and a histogram of rule firing rate was plotted. We selected the important regions of the histogram regarding to firing pattern of the rule. By choosing an appropriate threshold, a secondary rule reduction was done to generate a simplified model; remaining rules were best rules related to important cues of cABR. This model represents the input-output behavior of the brainstem in generating cABR to consonant-vowel /da/. The total error achieved by cross-validation of the model after an important rule selection is 0.1329 with a variance of 7.08×10-4. Nonlinear fuzzy based dynamic extraction of cABR signal is a valid approach for generating important features of cABR and a remarkable evidence of these signals can be represented by some spatial rules

[Electrophysiologic and behavioral assessment of hearing status in children with spastic diplegia]

High incidence of speech disorders in children with cerebral palsy could be related to a deficiency in processing of auditory stimuli. So it is vital to check out any peripheral or central disorders in auditory system using behvavioral and electrophysiological auditory tests. In a cross-sectional study, 15 children with spastic diplegia, mean age 5.77, SD 2.26 years, and 15 normal children, mean age 5.33, SD 1.80 years, were tested using pure tone audiometry, imittance and auditory brainstem responses. The results were compared between the two groups. Hearing thresholds and middle ear status were in normal range in all participants; however, contralateral acoustic reflex thresholds were mostly elevated. Comparing absolute latency and interpeak latency intervals of auditory brainstem responses between the two groups, absolute latency interval of later waves, and in specific the V wave, was significantly longer in diplegic children [p=0.04] resulting in a longer III-V interpeak latency intervals [p=0.02]. Neurological disorders in pont-o-reticulo-spinal pathway, pontine reticular nuclei and upper pons which are adjacent to adutory nuclei of lateral leminiscus and inferior colliculus result in auditory dys-synchrony and increased latency intervals in latter waves of auditory brainstem responses. This could also attributed to functional disorders in wave-generating sites in these patients

[Brainstem auditory evoked potential study in children with autism]

Autism is a neurodevelopmental disorder of the brain, which occures in first few years of life, and characterized by symptoms such as qualititative impairments in verbal and non verbal communication, reciprocal social interactions, inability to communicate with others, stereotyped patterns of behavior, loss of eye contact and inappropriate facial expressions. Its prevalence in 2-5 in 10000 children and is greater in boys. Due to retarded language development, differential diagnosis other than those used with communication, behavioral and sensorial deficits should be made with Sensorineural or conductive hearing loss. The aim of this study was to determine whether children with autism have abnormalities affecting the cohlear nerve or auditory pathway in brainstem. In this case- control study, auditory brainstem responses were recorded from 12 autistic children and 12 normal children aged 3-12 years in rehabilitation Zafar central in Tehran - Iran during 2005. Absolute latency values of waves I, III and V and interpeak latencies of I-III, III-V and I-V were compared with the results of 12 normal children as control group. Wave V could be traced down to 25 dB nHL in both normal and autistic groups. Absolute latency of Wave V and Interpeak latencies of III-V and I-V were significantly prolonged in Autisitc children in comparison with control group. This study showed a slowing in nerve conduction in auditory pathways in brainstem of autism patients. The brainstem lesion may be a part of neurological damage in autistic children that accounts for deviant language, cognition and social development. Prolongation of wave V, III-V and I-V IPLs can be a marker for early diagnosis of autism

[Identifying cochlear dead regions in hearing impaired children with the threshold equalizing noise test]

Regions in the cochlea with no [or very few] functioning inner hair cells and/or neurons are called dead regions. The aim of this study was to identify the cochlear dead regions in moderate to profound sensory neural hearing impaired children through the Threshold equalizing noise [TEN[HL]] test. In this cross-sectional study, the TEN[HL] was performed for the all frequencies available on test CD, on 30 children with ages ranging from five to forteen years [mean age, 8.5 +/- 2.8 years old]. In this study, 58.3% of ears were found to have a dead region for at least one frequency. Classifying by test frequencies, 20% were found to have a dead region, 24% to be inconclusive and 56% to have no dead regions. The difference between mean SNR[T] in ears with and without dead regions was statistically significant. The difference between mean absolute thresholds in two groups was statistically significant at 1000 Hz and below [p <0.05]. The results indicated a relatively high prevalence of dead regions in children with sensory neural hearing impairment, especially for frequencies at which the hearing loss exceeds 70 dB HL

[ effects of increasing the stimulus rate on auditory brainstem response latency in old population with normal hearing]

The auditory system changes by increasing age in both central and peripheral parts. The purpose of this study was to investigate the effect of the increasing the stimulus rate on auditory brainstem response [ABR] waves latency in old population with normal hearing. In this cross-sectional study click ABR test performed on 20 young normal-hearing subjects with mean age of 20.8 years old and 10 old normal-hearing subjects with mean age of 66.4 years old. ABR results with different stimulus rates were compared between two groups. ABR peak latencies and interpeak intervals were prolonged with increasing the click repetition rate. Peak latencies were slightly prolonged in older adults and the I-V interval did not differ with age but prolongation of III-V interval were significantly differs in older population compared to young adults. Using high click rates may sensitize the ABR to the identification of lesions of auditory nerve or brainstem, but before that, we need to know the normal range of different age groups, so that we can decide about probability of a retrocochlear lesion