The effects of inner ear abnormality on audibility have been explored since the early 20th century when sound detection measures were first used to define and quantify 'hearing loss'. The development in the 1970s of objective measures of cochlear hair cell function (cochlear microphonics, otoacoustic emissions, summating potentials) and auditory nerve/brainstem activity (auditory brainstem responses) have made it possible to distinguish both synaptic and auditory nerve disorders from sensory receptor loss. This distinction is critically important when considering aetiology and management. In this review we address the clinical and pathophysiological features of auditory neuropathy that distinguish site(s) of dysfunction. We describe the diagnostic criteria for: (i) presynaptic disorders affecting inner hair cells and ribbon synapses; (ii) postsynaptic disorders affecting unmyelinated auditory nerve dendrites; (iii) postsynaptic disorders affecting auditory ganglion cells and their myelinated axons and dendrites; and (iv) central neural pathway disorders affecting the auditory brainstem. We review data and principles to identify treatment options for affected patients and explore their benefits as a function of site of lesion.

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Pathophysiological mechanisms and functional hearing consequences of auditory neuropathy

Objective. Auditory neuropathy spectrum disorder (ANSD) affects approximately 10% of patients with sensorineural hearing loss. While many studies report abnormalities at the level of the cochlea, auditory nerve, and brainstem in children with ANSD, much less is known about their cortical development. We examined central auditory maturation in 21 children with ANSD. Design. Morphology, latency and amplitude of the P1 cortical auditory evoked potential (CAEP) were used to assess auditory cortical maturation. Children's scores on a measure of auditory skill development (IT-MAIS) were correlated with CAEPs. Study Sample. Participants were 21 children with ANSD. All were hearing aid users. Result. Children with ANSD exhibited differences in central auditory maturation. Overall, two-thirds of children revealed present P1 CAEP responses. Of these, just over one third (38%) showed normal P1 response morphology, latency and amplitude, while another third (33%) showed delayed P1 response latencies and signi...

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Cortical maturation and behavioral outcomes in children with auditory neuropathy spectrum disorder

The developing auditory cortex is highly plastic. As such, the cortex is both primed to mature normally and at risk for reorganizing abnormally, depending upon numerous factors that determine central maturation. From a clinical perspective, at least two major components of development can be manipulated: (1) input to the cortex and (2) the timing of cortical input. Children with sensorineural hearing loss (SNHL) and auditory neuropathy spectrum disorder (ANSD) have provided a model of early deprivation of sensory input to the cortex and demonstrated the resulting plasticity and development that can occur upon introduction of stimulation. In this article, we review several fundamental principles of cortical development and plasticity and discuss the clinical applications in children with SNHL and ANSD who receive intervention with hearing aids and/or cochlear implants.

Plasticity in the developing auditory cortex: evidence from children with sensorineural hearing loss and auditory neuropathy spectrum disorder.

Purpose of review The study summarizes supportive epidemiological data regarding the true co-occurrence (comorbidity) and course of mental disorders in children with intellectual disability/intellectual developmental disorders (ID/IDD) across the lifespan. Recent findings Published studies involving representative populations of children and adolescents with ID/IDD have demonstrated a three to four-fold increase in prevalence of co-occurring mental disorders. The effect of age, sex, and severity (mild, moderate, severe, and profound) and socioeconomic status on prevalence is currently not clearly understood. To date there are no prevalence estimates of co-occurring mental disorders in youth identified using the new DSM-5 (and proposed ICD-11) definition of ID/IDD using measures of intellectual functions and deficits in adaptive functioning with various severity levels defined on the basis of adaptive functioning, and not intellectual quotient scores. Summary The true relationship between two forms of morbidity remains complex and causal relationships that may be true for one disorder may not apply to another. The new conceptualization of ID/IDD offers a developmentally better informed psychobiological approach that can help distinguish co-occurrence of mental disorders within the neurodevelopmental section with onset during the developmental period as well as the later onset of other mental disorders.

The Co-Occurrence of Other Mental Disorders in Children and Adolescents With Intellectual Disability/Intellectual Developmental Disorder

https://escholarship.org/content/qt7g5966pk/qt7g5966pk.pdf?t=ojb733

N100 cortical potentials accompanying disrupted auditory nerve activity in auditory neuropathy (AN): effects of signal intensity and continuous noise.

Background
Present study investigated the relationship between speech identification scores in quiet and parameters of cortical potentials (latency of P1, N1, and P2; and amplitude of N1/P2) in individuals with auditory neuropathy.

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Speech identification and cortical potentials in individuals with auditory neuropathy

Background: There are many clinically available tests for the assessment of auditory processing skills in children and adults. However, there is limited data available on the maturational effects on the performance on these tests. Purpose: The current study investigated maturational effects on auditory processing abilities using three psychophysical measures: temporal modulation transfer function (TMTF), iterated ripple noise (IRN) perception, and spectral ripple discrimination (SRD). Research Design: A cross-sectional study. Three groups of subjects were tested: 10 adults (18–30 yr), 10 older children (12–18 yr), and 10 young children (8–11 yr) Data Collection and Analysis: Temporal envelope processing was measured by obtaining thresholds for amplitude modulation detection as a function of modulation frequency (TMTF; 4, 8, 16, 32, 64, and 128 Hz). Temporal fine structure processing was measured using IRN, and spectral processing was measured using SRD. Results: The results showed that young children had significantly higher modulation thresholds at 4 Hz (TMTF) compared to the other two groups and poorer SRD scores compared to adults. The results on IRN did not differ across groups. Conclusions: The results suggest that different aspects of auditory processing mature at different age periods and these maturational effects need to be considered while assessing auditory processing in children.

Assessing spectral and temporal processing in children and adults using temporal modulation transfer function (TMTF), Iterated Ripple Noise (IRN) perception, and spectral ripple discrimination (SRD).

Objectives To investigate the ability to identify consonant-vowel (CV) stimuli by individuals with auditory neuropathy (AN) when the envelope of the speech signal is enhanced by 15 dB for different modulation bandwidths (3 to 10 Hz; 3 to 20 Hz; 3 to 30 Hz; 3 to 60 Hz). Design Eight individuals with auditory neuropathy whose pure-tone thresholds ranged from 30 to 70 dB HL participated in the present study. Speech material consisted of five lists of CV, one unprocessed and four with envelope enhancement. The magnitude of envelope enhancement was 15 dB and the bandwidths used were 3 to 10 Hz, 3 to 20 Hz, 3 to 30 Hz, and 3 to 60 Hz. Results Speech identification scores improved when the envelope of the speech was enhanced. The improvement was greater for the broader bandwidth (3 to 30 Hz) conditions when compared with the smaller bandwidth (3 to 10 Hz and 3 to 20 Hz) conditions. In the unprocessed condition, manner of articulation was transmitted better than voicing and place of articulation. In the envelope-enhanced conditions, cues for manner and place of articulation were transmitted better than voicing. Conclusions Envelope enhancement using digital techniques improves speech perception by individuals with auditory neuropathy, and it may be a viable option for the rehabilitation of these individuals. However, the magnitude of envelope enhancement of speech required for maximal improvement of speech perception is yet to be determined.

Effect of envelope enhancement on speech perception in individuals with auditory neuropathy.

Aim 
The present study evaluated the relation between speech perception in the presence of background noise and temporal processing ability in listeners with Auditory Neuropathy (AN).


Method 
The study included two experiments. In the first experiment, temporal resolution of listeners with normal hearing and those with AN was evaluated using measures of temporal modulation transfer function and frequency modulation detection at modulation rates of 2 and 10 Hz. In the second experiment, speech perception in quiet and noise was evaluated at three signal to noise ratios (SNR) (0, 5, and 10 dB).


Results 
Results demonstrated that listeners with AN performed significantly poorer than normal hearing listeners in both amplitude modulation and frequency modulation detection, indicating significant impairment in extracting envelope as well as fine structure cues from the signal. Furthermore, there was significant correlation seen between measures of temporal resolution and speech perception in noise.


Conclusion 
Results suggested that an impaired ability to efficiently process envelope and fine structure cues of the speech signal may be the cause of the extreme difficulties faced during speech perception in noise by listeners with AN.

/pdf/temporal-processing-and-speech-perception-in-noise-by-4yghfjynrn.pdf

Temporal Processing and Speech Perception in Noise by Listeners with Auditory Neuropathy

Individuals with auditory neuropathy (AN) often suffer from temporal processing deficits causing speech perception difficulties. In the present study an envelope enhancement scheme that incorporated envelope expansion was used to reduce the effects of temporal deficits. The study involved two experiments. In the first experiment, to simulate the effects of reduced temporal resolution, temporally smeared speech stimuli were presented to listeners with normal hearing. The results revealed that temporal smearing of the speech signal reduced identification scores. With the envelope enhancement of the speech signal prior to being temporally smeared, identification scores improved significantly compared to temporally smeared condition. The second experiment assessed speech perception in twelve individuals with AN, using unprocessed and envelope-enhanced speech signals. The results revealed improvement in speech identification scores for the majority of individuals with AN when the envelope of the speech signal ...

Vijaya Kumar Narne

Papers

Speech identification and cortical potentials in individuals with auditory neuropathy

Assessing spectral and temporal processing in children and adults using temporal modulation transfer function (TMTF), Iterated Ripple Noise (IRN) perception, and spectral ripple discrimination (SRD).

Effect of envelope enhancement on speech perception in individuals with auditory neuropathy.

Temporal Processing and Speech Perception in Noise by Listeners with Auditory Neuropathy

Perception of speech with envelope enhancement in individuals with auditory neuropathy and simulated loss of temporal modulation processing