Pádraig T. Kitterick

Bilateral or unilateral cochlear implantation for deaf children: an observational study

Objective Cochlear implantation in one ear (unilateral implantation) has been the standard treatment for severe-profound childhood deafness. We assessed whether cochlear implantation in both ears (bilateral implantation) is associated with better listening skills, higher health-related quality of life (health utility) and higher general quality of life (QOL) than unilateral implantation. Design Cross-sectional observational study. Setting University of York. Participants Fifty severely-profoundly deaf and 56 normally-hearing children recruited via a charity, the UK National Health Service and schools. Interventions Thirty of the deaf children had received bilateral cochlear implants; 20 had unilateral cochlear implants. Main outcome measures Performance measures of children’s listening skills; parental-proxy valuations of the deaf children’s health utility obtained with the Health Utilities Index Mark 3 and of their QOL obtained with a visual analogue scale. Results On average, bilaterally-implanted children performed significantly better than unilaterally implanted children on tests of sound localisation and speech perception in noise. After conservative imputation of missing data and while controlling for confounds, bilateral implantation was associated with increases of 18.5% in accuracy of sound localisation (95% CI 5.9 to 31.1) and of 3.7 dB in speech perception in noise (95% CI 0.9 to 6.5). Bilaterally-implanted children did not perform as well as normally-hearing children, on average. Bilaterally- and unilaterally-implanted children did not differ significantly in parental ratings of health utility (difference in medians 0.05, p>0.05) or QOL (difference in medians 0.01, p>0.05). Conclusions Compared with unilateral cochlear implantation, bilateral implantation is associated with better listening skills in severely-profoundly deaf children.

Evidence for Opponent Process Analysis of Sound Source Location in Humans

Research with barn owls suggested that sound source location is represented topographically in the brain by an array of neurons each tuned to a narrow range of locations. However, research with small-headed mammals has offered an alternative view in which location is represented by the balance of activity in two opponent channels broadly tuned to the left and right auditory space. Both channels may be present in each auditory cortex, although the channel representing contralateral space may be dominant. Recent studies have suggested that opponent channel coding of space may also apply in humans, although these studies have used a restricted set of spatial cues or probed a restricted set of spatial locations, and there have been contradictory reports as to the relative dominance of the ipsilateral and contralateral channels in each cortex. The current study used electroencephalography (EEG) in conjunction with sound field stimulus presentation to address these issues and to inform the development of an explicit computational model of human sound source localization. Neural responses were compatible with the opponent channel account of sound source localization and with contralateral channel dominance in the left, but not the right, auditory cortex. A computational opponent channel model reproduced every important aspect of the EEG data and allowed inferences about the width of tuning in the spatial channels. Moreover, the model predicted the oft-reported decrease in spatial acuity measured psychophysically with increasing reference azimuth. Predictions of spatial acuity closely matched those measured psychophysically by previous authors.

Concurrent sound segregation based on inharmonicity and onset asynchrony.

To explore the neural processes underlying concurrent sound segregation, auditory evoked fields (AEFs) were measured using magnetoencephalography (MEG). To induce the segregation of two auditory objects we manipulated harmonicity and onset synchrony. Participants were presented with complex sounds with (i) all harmonics in-tune (ii) the third harmonic mistuned by 8% of its original value (iii) the onset of the third harmonic delayed by 160 ms compared to the other harmonics. During recording, participants listened to the sounds and performed an auditory localisation task whereas in another session they ignored the sounds and performed a visual localisation task. Active and passive listening was chosen to evaluate the contribution of attention on sound segregation. Both cues - inharmonicity and onset asynchrony - elicited sound segregation, as participants were more likely to report correctly on which side they heard the third harmonic when it was mistuned or delayed compared to being in-tune with all other harmonics. AEF activity associated with concurrent sound segregation was identified over both temporal lobes. We found an early deflection at approximately 75 ms (P75m) after sound onset, probably reflecting an automatic registration of the mistuned harmonic. Subsequent deflections, the object-related negativity (ORNm) and a later displacement (P230m) seem to be more general markers of concurrent sound segregation, as they were elicited by both mistuning and delaying the third harmonic. Results indicate that the ORNm reflects relatively automatic, bottom-up sound segregation processes, whereas the P230m is more sensitive to attention, especially with inharmonicity as the cue for concurrent sound segregation.

Spatiotemporal reconstruction of the auditory steady-state response to frequency modulation using magnetoencephalography

The aim of this study was to investigate the mechanisms involved in the perception of perceptually salient frequency modulation (FM) using auditory steady-state responses (ASSRs) measured with magnetoencephalography (MEG). Previous MEG studies using frequency-modulated amplitude modulation as stimuli (Luo et al., 2006, 2007) suggested that a phase modulation encoding mechanism exists for low (<5 Hz) FM modulation frequencies but additional amplitude modulation encoding is required for faster FM modulation frequencies. In this study single-cycle sinusoidal FM stimuli were used to generate the ASSR. The stimulus was either an unmodulated 1-kHz sinusoid or a 1-kHz sinusoid that was frequency-modulated with a repetition rate of 4, 8, or 12 Hz. The fast Fourier transform (FFT) of each MEG channel was calculated to obtain the phase and magnitude of the ASSR in sensor-space and multivariate Hotellings T(2) statistics were used to determine the statistical significance of ASSRs. MEG beamformer analyses were used to localise the ASSR sources. Virtual electrode analyses were used to reconstruct the time series at each source. FFTs of the virtual electrode time series were calculated to obtain the amplitude and phase characteristics of each source identified in the beamforming analyses. Multivariate Hotellings T(2) statistics were used to determine the statistical significance of these reconstructed ASSRs. The results suggest that the ability of auditory cortex to phase-lock to FM is dependent on the FM pulse rate and that the ASSR to FM is lateralised to the right hemisphere.

The AB-York crescent of sound: An apparatus for assessing spatial-listening skills in children and adults

Abstract Modern health services need efficient tools for measuring outcomes from interventions, that is, tools of proven efficacy which make minimal demands on the time of clinicians in learning to administer tests and in interpreting results. This paper describes an apparatus designed to meet those requirements. The apparatus administers performance tests of spatial listening for children and adults with unilateral and bilateral cochlear implants. The apparatus was designed with guidance from clinicians. It possesses three key attributes: it is simple to use; the results of tests are scored automatically and are compared with reference data; the apparatus generates comprehensive personalized reports for individual participants that can be included in clinical notes. This paper describes the apparatus and reports results of a test measuring spatial release from masking of speech which illustrates the compatibility between the new apparatus and an older apparatus with which the reference data were gathered.

Identification and evaluation of cochlear implant candidates with asymmetrical hearing loss

Objective: Recommendation for cochlear implant (CI) treatment for individuals with severe to profound single-sided deafness (SSD) and asymmetrical hearing loss (AHL) is on the rise. This raises the need for greater consistency in the definition of CI candidacy for these cases and in the assessment methods of patient-related benefits to permit effective comparison and interpretation of the outcomes with both conventional and implantable options across studies. Method: During a dedicated seminar on implant treatment in AHL patients, the panellists of the closing round table reviewed the clinical experience presented with the aim to define clear audiometric characteristics for both AHL and SSD cases, as well as a common data set enabling consistent evaluation of hearing benefits in this population. Conclusions: The panellists agreed on a clear differentiation between AHL and SSD CI candidates, defining average pure-tone thresholds up to 4 kHz for better and poorer ears. Agreement was reached on a minimum set of assessment procedures, and included the necessity of trials with conventional CROS/BICROS hearing aids and bone conduction devices before considering CI treatment. Objective assessment of sound localisation abilities was identified as the most relevant criterion to quantify performance before and after treatment. In parallel, subjective assessment of overall hearing ability was recommended via the Speech, Spatial and Qualities of hearing questionnaire. Longitudinal follow-up of these parameters and the hours of daily use were considered essential to reflect the potential treatment benefits for this population. The consistency in the data collection and its report will further support health authorities in their decision on acceptable gains from available hearing loss treatment options.

Speech-evoked activation in adult temporal cortex measured using functional near-infrared spectroscopy (fNIRS): Are the measurements reliable?

Functional near-infrared spectroscopy (fNIRS) is a silent, non-invasive neuroimaging technique that is potentially well suited to auditory research. However, the reliability of auditory-evoked activation measured using fNIRS is largely unknown. The present study investigated the test-retest reliability of speech-evoked fNIRS responses in normally-hearing adults. Seventeen participants underwent fNIRS imaging in two sessions separated by three months. In a block design, participants were presented with auditory speech, visual speech (silent speechreading), and audiovisual speech conditions. Optode arrays were placed bilaterally over the temporal lobes, targeting auditory brain regions. A range of established metrics was used to quantify the reproducibility of cortical activation patterns, as well as the amplitude and time course of the haemodynamic response within predefined regions of interest. The use of a signal processing algorithm designed to reduce the influence of systemic physiological signals was found to be crucial to achieving reliable detection of significant activation at the group level. For auditory speech (with or without visual cues), reliability was good to excellent at the group level, but highly variable among individuals. Temporal-lobe activation in response to visual speech was less reliable, especially in the right hemisphere. Consistent with previous reports, fNIRS reliability was improved by averaging across a small number of channels overlying a cortical region of interest. Overall, the present results confirm that fNIRS can measure speech-evoked auditory responses in adults that are highly reliable at the group level, and indicate that signal processing to reduce physiological noise may substantially improve the reliability of fNIRS measurements.

Hearing Instruments for Unilateral Severe-to-Profound Sensorineural Hearing Loss in Adults: A Systematic Review and Meta-Analysis

Objectives: A systematic review of the literature and meta-analysis was conducted to assess the nature and quality of the evidence for the use of hearing instruments in adults with a unilateral severe to profound sensorineural hearing loss. Design: The PubMed, EMBASE, MEDLINE, Cochrane, CINAHL, and DARE databases were searched with no restrictions on language. The search included articles from the start of each database until February 11, 2015. Studies were included that (a) assessed the impact of any form of hearing instrument, including devices that reroute signals between the ears or restore aspects of hearing to a deaf ear, in adults with a sensorineural severe to profound loss in one ear and normal or near-normal hearing in the other ear; (b) compared different devices or compared a device with placebo or the unaided condition; (c) measured outcomes in terms of speech perception, spatial listening, or quality of life; (d) were prospective controlled or observational studies. Studies that met prospectively defined criteria were subjected to random effects meta-analyses. Results: Twenty-seven studies reported in 30 articles were included. The evidence was graded as low-to-moderate quality having been obtained primarily from observational before-after comparisons. The meta-analysis identified statistically significant benefits to speech perception in noise for devices that rerouted the speech signals of interest from the worse ear to the better ear using either air or bone conduction (mean benefit, 2.5 dB). However, these devices also degraded speech understanding significantly and to a similar extent (mean deficit, 3.1 dB) when noise was rerouted to the better ear. Data on the effects of cochlear implantation on speech perception could not be pooled as the prospectively defined criteria for meta-analysis were not met. Inconsistency in the assessment of outcomes relating to sound localization also precluded the synthesis of evidence across studies. Evidence for the relative efficacy of different devices was sparse but a statistically significant advantage was observed for rerouting speech signals using abutment-mounted bone conduction devices when compared with outcomes after preoperative trials of air conduction devices when speech and noise were colocated (mean benefit, 1.5 dB). Patients reported significant improvements in hearing-related quality of life with both rerouting devices and following cochlear implantation. Only two studies measured health-related quality of life and findings were inconclusive. Conclusions: Devices that reroute sounds from an ear with a severe to profound hearing loss to an ear with minimal hearing loss may improve speech perception in noise when signals of interest are located toward the impaired ear. However, the same device may also degrade speech perception as all signals are rerouted indiscriminately, including noise. Although the restoration of functional hearing in both ears through cochlear implantation could be expected to provide benefits to speech perception, the inability to synthesize evidence across existing studies means that such a conclusion cannot yet be made. For the same reason, it remains unclear whether cochlear implantation can improve the ability to localize sounds despite restoring bilateral input. Prospective controlled studies that measure outcomes consistently and control for selection and observation biases are required to improve the quality of the evidence for the provision of hearing instruments to patients with unilateral deafness and to support any future recommendations for the clinical management of these patients.

Improving health-related quality of life in single-sided deafness: a systematic review and meta-analysis

Unilateral severe-to-profound hearing loss, or single-sided deafness (SSD), impairs listening abilities supported by the use of two ears, including speech perception in background noise and sound localisation. Hearing-assistive devices can aid listening by re-routing sounds from the impaired to the non-impaired ear or by restoring input to the impaired ear. A systematic review of the literature examined the impact of hearing-assistive devices on the health-related quality of life (HRQoL) of adults with SSD as measured using generic and disease-specific instruments. A majority of studies used observational designs, and the quality of the evidence was low to moderate. Only two studies used generic instruments. A mixed-effect meta-analysis of disease-specific measures suggested that hearing-assistive devices have a small-to-medium impact on HRQoL. The Speech, Spatial and Qualities of Hearing Scale and the Health Utilities Index Mark 3 (HUI3) were identified as instruments that are sensitive to device-related changes in disease-specific and generic HRQoL, respectively.

Benefit of temporal fine structure to speech perception in noise measured with controlled temporal envelopes.

Previous studies have assessed the importance of temporal fine structure (TFS) for speech perception in noise by comparing the performance of normal-hearing listeners in two conditions. In one condition, the stimuli have useful information in both their temporal envelopes and their TFS. In the other condition, stimuli are vocoded and contain useful information only in their temporal envelopes. However, these studies have confounded differences in TFS with differences in the temporal envelope. The present study manipulated the analytic signal of stimuli to preserve the temporal envelope between conditions with different TFS. The inclusion of informative TFS improved speech-reception thresholds for sentences presented in steady and modulated noise, demonstrating that there are significant benefits of including informative TFS even when the temporal envelope is controlled. It is likely that the results of previous studies largely reflect the benefits of TFS, rather than uncontrolled effects of changes in the temporal envelope.