David R. Moore

The descending corticocollicular pathway mediates learning-induced auditory plasticity

Descending projections from sensory areas of the cerebral cortex are among the largest pathways in the brain, suggesting that they are important for subcortical processing. Although corticofugal inputs have been shown to modulate neuronal responses in the thalamus and midbrain, the behavioral importance of these changes remains unknown. In the auditory system, one of the major descending pathways is from cortical layer V pyramidal cells to the inferior colliculus in the midbrain. We examined the role of these neurons in experience-dependent recalibration of sound localization in adult ferrets by selectively killing the neurons using chromophore-targeted laser photolysis. When provided with appropriate training, animals normally relearn to localize sound accurately after altering the spatial cues available by reversibly occluding one ear. However, this ability was lost after eliminating corticocollicular neurons, whereas normal sound-localization accuracy was unaffected. The integrity of this descending pathway is therefore critical for learning-induced localization plasticity.

Susceptibility of developing cochlear nucleus neurons to deafferentation-induced death abruptly ends just before the onset of hearing

To investigate the ability of developing cochlear nucleus (CN) neurons to survive in the absence of afferent input, left cochlear removals were performed on gerbils at 2 day intervals from postnatal (P)3 to P11, and at P18 and P93. After a 3 month postsurgical survival period, Nissl‐stained frontal sections through the brainstem were analyzed under the light microscope. CN volume, anteroventral cochlear nucleus (AVCN) neuron cross‐sectional area, and total number of neurons in the CN were measured on both sides of the brain.

Nature of Auditory Processing Disorder in Children

OBJECTIVE: We tested the specific hypothesis that the presentation of auditory processing disorder (APD) is related to a sensory processing deficit. METHODS: Randomly chosen, 6- to 11-year-old children with normal hearing (N = 1469) were tested in schools in 4 regional centers across the United Kingdom. Caregivers completed questionnaires regarding their participating childrens listening and communication skills. Children completed a battery of audiometric, auditory processing (AP), speech-in-noise, cognitive (IQ, memory, language, and literacy), and attention (auditory and visual) tests. AP measures separated the sensory and nonsensory contributions to spectral and temporal perception. RESULTS: AP improved with age. Poor-for-age AP was significantly related to poor cognitive, communication, and speech-in-noise performance (P < .001). However, sensory elements of perception were only weakly related to those performance measures (r < 0.1), and correlations between auditory perception and cognitive scores were generally low (r = 0.1–0.3). Multivariate regression analysis showed that response variability in the AP tests, reflecting attention, and cognitive scores were the best predictors of listening, communication, and speech-in-noise skills. CONCLUSIONS: Presenting symptoms of APD were largely unrelated to auditory sensory processing. Response variability and cognitive performance were the best predictors of poor communication and listening. We suggest that APD is primarily an attention problem and that clinical diagnosis and management, as well as further research, should be based on that premise.

Beyond cochlear implants: awakening the deafened brain

Cochlear implants have provided hearing to more than 120,000 deaf people. Recent surgical developments include direct electrical stimulation of the brain, bilateral implants and implantation in children less than 1 year old. However, research is beginning to refocus on the role of the brain in providing benefits to implant users. The auditory system is able to use the highly impoverished input provided by implants to interpret speech, but this only works well in those who have developed language before their deafness or in those who receive their implant at a very young age. We discuss recent evidence suggesting that developing the ability of the brain to learn how to use an implant may be as important as further improvements of the implant technology.

Discrimination learning induced by training with identical stimuli

Sensory stimuli become easier to detect or distinguish with practice. It is generally assumed that the task-relevant stimulus dimension becomes increasingly more salient as a result of attentively performing the task at a level that is neither too easy nor too difficult. However, here we show improved auditory frequency discrimination following training with physically identical tones that were impossible to discriminate. We also show that learning transfers across tone frequencies and across modalities: training on a silent visuospatial computer game improved thresholds on the auditory discrimination task. We suggest that three processes are necessary for optimal perceptual learning: sensitization through exposure to the stimulus, modality- and dimension-specific attention, and general arousal.

Listening effort and fatigue: what exactly are we measuring? A British Society of Audiology Cognition in Hearing Special Interest Group 'white paper'.

Abstract Objective: There is growing interest in the concepts of listening effort and fatigue associated with hearing loss. However, the theoretical underpinnings and clinical meaning of these concepts are unclear. This lack of clarity reflects both the relative immaturity of the field and the fact that research studies investigating listening effort and fatigue have used a variety of methodologies including self-report, behavioural, and physiological measures. Design: This discussion paper provides working definitions for listening effort and listening-related fatigue. Using these definitions as a framework, methodologies to assess these constructs are reviewed. Results: Although each technique attempts to characterize the same construct (i.e. the clinical presentation of listening effort and fatigue), different assumptions are often made about the nature of these phenomena and their behavioural and physiological manifestations. Conclusion: We suggest that researchers consider these assumptions when interpreting their data and, where possible, make predictions based on current theoretical knowledge to add to our understanding of the underlying mechanisms of listening effort and listening-related fatigue. Foreword Following recent interest in the cognitive involvement in hearing, the British Society of Audiology (BSA) established a Special Interest Group on Cognition in Hearing in May 2013. In an exploratory group meeting, the ambiguity surrounding listening effort and fatigue was discussed. To address this problem, the group decided to develop a ‘white paper’ on listening effort and fatigue. This is a discussion document followed by an international set of commentaries from leading researchers in the field. An approach was made to the editor of the International Journal of Audiology who agreed to this suggestion. This paper, and the associated commentaries that follow, are the result.

Otitis media, hearing loss, and language learning: Controversies and current research

ABSTRACT. This article reviews research on the possible linkage of otitis media with effusion (OME) to childrens hearing and development, identifies gaps, and directions for research, and discusses implications for healthcare practices. About half of children with an episode of OME experience a mild hearing loss while about 5-10% of children have moderate hearing loss. Recent prospective and randomized clinical trials suggest none to very small negative associations of OME to childrens later language development. Based on both retrospective and prospective longitudinal studies, associations between OME and perceiving speech in noise and tasks that require equal binaural hearing have been reported but have not been adequately studied with regard to functional outcomes. Thus, on average, for typically developing children, OME may not be a substantial risk factor for later speech and language development or academic achievement. However, these conclusions should be interpreted cautiously, since most of these studies used OME rather than hearing loss as the independent variable (although hearing loss rather than OME is hypothesized to affect language development) and many studies did not control for important confounding variables such as socioeconomic status (SES).

Anatomy and Physiology of Binaural Hearing

Binaural hearing improves performance in most auditory tasks and is essential for some. This paper introduces the brain stem pathways and nuclei involved in binaural interaction and outlines some recent approaches to understanding binaural mechanisms. It also provides examples of basic science approaches to the effects of infant hearing loss on those pathways and mechanisms. Binaural interaction occurs primarily and almost simultaneously at three levels of the brain: the superior olivary complex (SOC), the nuclei of the lateral lemniscus (NLL) and the inferior colliculus (IC). The SOC derives its input from the anterior ventral cochlear nucleus (CN) through branching axons that innervate several SOC subdivisions on both sides of the brain. At least some of these anteroventral CN axons project on up to the contralateral NLL and IC. The IC and NLL also receive direct, major projections from the contralateral CN, via the dorsal and intermediate acoustic striae, and from the SOC bilaterally. The IC receives additional input from the NLL bilaterally, and is thus innervated by every nuclear group within the auditory brain stem. There is little evidence for strict, functional segregation in these binaural pathways, although subdivisions of the SOC appear to be predominantly involved in analysing either interaural time or level differences (ITD, ILD). ITD- and ILD-sensitive neurones are also found in abundance in the central IC. There is emerging evidence that binaural information is coupled with spectral cues derived from the outer ear in several auditory mid-brain regions [the NLL, the external IC and the superior colliculus (SC)] to produce topographic representations of auditory space. Throughout the higher auditory system the response of neurones to stimulation of each ear is either excitatory or inhibitory, and there is a spatial segregation of neurones receiving predominantly excitatory or inhibitory input from the ipsilateral ear in both the medial geniculate body of the thalamus and the auditory cortex. Neonatal, unilateral hearing loss leads to a rearrangement of binaural connections in the auditory brain stem, to changes in the physiology of IC neurones in response to stimulation of the normal ear and to compensatory alterations in the auditory space map in the SC. The same hearing losses in adulthood do not produce these changes. The evidence from this and other work suggests that binaural mechanisms are more sensitive to hearing loss, over a longer developmental period, than mechanisms subserving monaural processing.

Down-regulation of inhibition following unilateral deafening

Physiological and neurochemical experiments described here suggest that unilateral deafening causes a reduction in inhibition in the adult gerbil inferior colliculus (IC) contralateral to the deafened ear. Multiple-unit recordings were made from single electrode penetrations in the IC prior to and directly after contralateral cochlear ablation. These recordings showed up to 60% increases in the proportion of sampled loci at which neural activity excited by ipsilateral stimulation was observed after the ablation. Novel excitatory responses were evident within minutes of the ablation. Western blotting for glutamic acid decarboxylase protein levels showed significant decreases in the IC contralateral to cochlear ablation, relative to those in the ipsilateral IC, at 24 h and 7 days survival after the ablation. Four hour or 1 year survival post-ablation did not produce significant contralateral/ipsilateral differences in relation to the control group. Taken together, these results suggest the presence of at least two, short-term mechanisms involved in the central response to cochlear removal, both of which appear to implicate a decreased inhibitory influence. One is a very rapid, stimulus-related, functional unmasking. The other is a more delayed reduction in the capacity of gamma-aminobutyric acid synthesis in the IC.

Discrimination Training of Phonemic Contrasts Enhances Phonological Processing in Mainstream School Children.

Auditory perceptual learning has been proposed as effective for remediating impaired language and for enhancing normal language development. We examined the effect of phonemic contrast discrimination training on the discrimination of whole words and on phonological awareness in 8- to 10-year-old mainstream school children. Eleven phonemic contrast continua were synthesised using linear interpolation coding from real speaker endpoints. Thirty children were pre-tested on the Word Discrimination Test (WDT) and the Phonological Assessment Battery (PhAB). Eighteen then trained for 12 x 30min sessions over 4 weeks using an adaptive three interval two alternative phonemic matching task. The remaining children participated in regular classroom activities. In Post-testing, trained children significantly increased their age-equivalent scores on both the WDT and PhAB by about 2 years. For the PhAB, no improvement was found in the controls. Enhanced performance in the trained children was maintained in a delayed test 5-6 weeks following training. Enhancements on the trained discriminations were weak and variable. The results indicate a dramatic improvement in phonological awareness following phonemic discrimination training without matching perceptual learning.