Capabilities, opportunities and motivations of staff to provide hearing support to long-term care home residents with dementia.

OBJECTIVE: Many long-term care home (LTCH) residents have dementia and hearing loss, causing communication difficulties and agitation. Residents rely on staff for hearing support, but provision is often inconsistent. This study used the Behaviour Change Wheel's Capability, Opportunity and Motivation model to understand why LTCH staff do or do not, provide hearing support to residents with dementia who they believe could benefit from it. DESIGN: An online survey exploring hearing support provision, capabilities, opportunities, motivations and demographics. Data were analysed using descriptive statistics, within-participants ANOVA and multiple linear regression. STUDY SAMPLE: 165 LTCH staff. RESULTS: Staff provided hearing support to 50% of residents with dementia who they thought would benefit. Self-reported physical and psychological capabilities (skills/knowledge) were significantly higher than physical opportunity (having time/resources). The physical capability was significantly higher than social opportunity (collaborative working) and reflective motivation (feeling motivated). Lower levels of hearing support provision were predicted by LTCH funding (private vs. local authority), job role (care assistant vs. nurse) and fewer physical opportunities. CONCLUSIONS: Boosting capabilities through training alone may not be as effective as increasing opportunities via environmental restructuring. Opportunities may include strengthening working relationships with audiologists and ensuring hearing and communication aids are available within LTCHs.

Associations between pre-stimulus alpha power, hearing level and performance in a digits-in-noise task.

OBJECTIVE: Baseline electroencephalography (EEG) alpha power, i.e. that measured prior to stimulus presentation, is a potential objective predictor of task performance. Here we assessed the predictive power of EEG alpha on performance accuracy in a digits-in-noise recognition task, factoring in hearing thresholds and age. DESIGN: EEG alpha power, recorded while participants listened to target digits presented in a noise background, was analysed during two different baseline periods: i) a pre-stimulus baseline (pre-STIM) free from any acoustic stimulus, and ii) a pre-target baseline (pre-TARG) recorded in background noise only. STUDY SAMPLE: Eighty-five participants with either normal hearing or aided hearing impairment (age range: 55-85 years old, 42 male). RESULTS: Hierarchical multiple regression analyses indicated that i) lower hearing thresholds and, to a lesser extent, higher pre-STIM alpha power were associated with improved performance accuracy ii) alpha power in pre-STIM and pre-TARG were highly correlated across individuals but pre-TARG alpha power was not a significant predictor of performance accuracy. CONCLUSION: Investigations of baseline EEG alpha power as a predictor of speech-in-noise performance accuracy should control for associations between hearing thresholds and measures of EEG baseline periods.

Financial reward has differential effects on behavioural and self-report measures of listening effort.

OBJECTIVES: To investigate the effects of listening demands and motivation on listening effort (LE) in a novel speech recognition task. DESIGN: We manipulated listening demands and motivation using vocoded speech and financial reward, respectively, and measured task performance (correct response rate) and indices of LE (response times (RTs), subjective ratings of LE and likelihood of giving up). Effects of inter-individual differences in cognitive skills and personality on task performance and LE were also assessed within the context of the Cognitive Energetics Theory (CET). STUDY SAMPLE: Twenty-four participants with normal-hearing (age range: 19 - 33 years, 6 male). RESULTS: High listening demands decreased the correct response rate and increased RTs, self-rated LE and self-rated likelihood of giving up. High financial reward increased subjective LE ratings only. Mixed-effects modelling showed small fixed effects for competitiveness on LE measured using RTs. Small fixed effects were found for cognitive skills (lexical decision RTs and backwards digit span) on LE measured using RTs and correct response rate, respectively. CONCLUSIONS: The effects of listening demands on LE in the speech recognition task aligned with CET, whereas predictions regarding the influence of motivation, cognitive skills and personality were only partially supported.

Dimensions of self-reported listening effort and fatigue on a digits-in-noise task, and association with baseline pupil size and performance accuracy.

OBJECTIVE: Pupillometry is sensitive to cognitive resource allocation and has been used as a potential measure of listening-related effort and fatigue. We investigated associations between peak pupil diameter, pre-stimulus pupil diameter, performance on a listening task, and the dimensionality of self-reported outcomes (task-related listening effort and fatigue). DESIGN: Pupillometry was recorded while participants performed a speech-in-noise task. Participants rated their experience of listening effort and fatigue using the NASA-Task Load Index (NASA-TLX) and the Visual Analogue Scale of Fatigue (VAS-F), respectively. The dimensionality of the NASA-TLX and the VAS-F was investigated using factor analysis. STUDY SAMPLE: 82 participants with either normal hearing or aided hearing impairment (age range: 55-85 years old, 43 male). RESULTS: Hierarchal linear regression analyses suggested that pre-stimulus pupil diameter predicts a dimension of self-reported fatigue, which we interpreted as tiredness/drowsiness, and listening task performance when controlling for hearing level and age: Larger pre-stimulus pupil diameter was associated with less tiredness/drowsiness and better task performance. CONCLUSION: Pre-stimulus pupil diameter is a potential index of listening fatigue associated with speech processing in challenging listening conditions. To our knowledge, this is the first investigation of the associations between pre-stimulus pupil diameter and self-reported ratings of listening effort and fatigue.

The association between subcortical and cortical fMRI and lifetime noise exposure in listeners with normal hearing thresholds.

In animal models, exposure to high noise levels can cause permanent damage to hair-cell synapses (cochlear synaptopathy) for high-threshold auditory nerve fibers without affecting sensitivity to quiet sounds. This has been confirmed in several mammalian species, but the hypothesis that lifetime noise exposure affects auditory function in humans with normal audiometric thresholds remains unconfirmed and current evidence from human electrophysiology is contradictory. Here we report the auditory brainstem response (ABR), and both transient (stimulus onset and offset) and sustained functional magnetic resonance imaging (fMRI) responses throughout the human central auditory pathway across lifetime noise exposure. Healthy young individuals aged 25-40 years were recruited into high (n = 32) and low (n = 30) lifetime noise exposure groups, stratified for age, and balanced for audiometric threshold up to 16 kHz fMRI demonstrated robust broadband noise-related activity throughout the auditory pathway (cochlear nucleus, superior olivary complex, nucleus of the lateral lemniscus, inferior colliculus, medial geniculate body and auditory cortex). fMRI responses in the auditory pathway to broadband noise onset were significantly enhanced in the high noise exposure group relative to the low exposure group, differences in sustained fMRI responses did not reach significance, and no significant group differences were found in the click-evoked ABR. Exploratory analyses found no significant relationships between the neural responses and self-reported tinnitus or reduced sound-level tolerance (symptoms associated with synaptopathy). In summary, although a small effect, these fMRI results suggest that lifetime noise exposure may be associated with central hyperactivity in young adults with normal hearing thresholds.

Measures of Listening Effort Are Multidimensional.

OBJECTIVES: Listening effort can be defined as the cognitive resources required to perform a listening task. The literature on listening effort is as confusing as it is voluminous: measures of listening effort rarely correlate with each other and sometimes result in contradictory findings. Here, we directly compared simultaneously recorded multimodal measures of listening effort. After establishing the reliability of the measures, we investigated validity by quantifying correlations between measures and then grouping-related measures through factor analysis. DESIGN: One hundred and sixteen participants with audiometric thresholds ranging from normal to severe hearing loss took part in the study (age range: 55 to 85 years old, 50.3% male). We simultaneously measured pupil size, electroencephalographic alpha power, skin conductance, and self-report listening effort. One self-report measure of fatigue was also included. The signal to noise ratio (SNR) was adjusted at 71% criterion performance using sequences of 3 digits. The main listening task involved correct recall of a random digit from a sequence of six presented at a SNR where performance was around 82 to 93%. Test-retest reliability of the measures was established by retesting 30 participants 7 days after the initial session. RESULTS: With the exception of skin conductance and the self-report measure of fatigue, interclass correlation coefficients (ICC) revealed good test-retest reliability (minimum ICC: 0.71). Weak or nonsignificant correlations were identified between measures. Factor analysis, using only the reliable measures, revealed four underlying dimensions: factor 1 included SNR, hearing level, baseline alpha power, and performance accuracy; factor 2 included pupillometry; factor 3 included alpha power (during speech presentation and during retention); factor 4 included self-reported listening effort and baseline alpha power. CONCLUSIONS: The good ICC suggests that poor test reliability is not the reason for the lack of correlation between measures. We have demonstrated that measures traditionally used as indicators of listening effort tap into multiple underlying dimensions. We therefore propose that there is no "gold standard" measure of listening effort and that different measures of listening effort should not be used interchangeably. When choosing method(s) to measure listening effort, the nature of the task and aspects of increased listening demands that are of interest should be taken into account. The findings of this study provide a framework for understanding and interpreting listening effort measures.

Magnified Neural Envelope Coding Predicts Deficits in Speech Perception in Noise.

Verbal communication in noisy backgrounds is challenging. Understanding speech in background noise that fluctuates in intensity over time is particularly difficult for hearing-impaired listeners with a sensorineural hearing loss (SNHL). The reduction in fast-acting cochlear compression associated with SNHL exaggerates the perceived fluctuations in intensity in amplitude-modulated sounds. SNHL-induced changes in the coding of amplitude-modulated sounds may have a detrimental effect on the ability of SNHL listeners to understand speech in the presence of modulated background noise. To date, direct evidence for a link between magnified envelope coding and deficits in speech identification in modulated noise has been absent. Here, magnetoencephalography was used to quantify the effects of SNHL on phase locking to the temporal envelope of modulated noise (envelope coding) in human auditory cortex. Our results show that SNHL enhances the amplitude of envelope coding in posteromedial auditory cortex, whereas it enhances the fidelity of envelope coding in posteromedial and posterolateral auditory cortex. This dissociation was more evident in the right hemisphere, demonstrating functional lateralization in enhanced envelope coding in SNHL listeners. However, enhanced envelope coding was not perceptually beneficial. Our results also show that both hearing thresholds and, to a lesser extent, magnified cortical envelope coding in left posteromedial auditory cortex predict speech identification in modulated background noise. We propose a framework in which magnified envelope coding in posteromedial auditory cortex disrupts the segregation of speech from background noise, leading to deficits in speech perception in modulated background noise.SIGNIFICANCE STATEMENT People with hearing loss struggle to follow conversations in noisy environments. Background noise that fluctuates in intensity over time poses a particular challenge. Using magnetoencephalography, we demonstrate anatomically distinct cortical representations of modulated noise in normal-hearing and hearing-impaired listeners. This work provides the first link among hearing thresholds, the amplitude of cortical representations of modulated sounds, and the ability to understand speech in modulated background noise. In light of previous work, we propose that magnified cortical representations of modulated sounds disrupt the separation of speech from modulated background noise in auditory cortex.

Causal cortical dynamics of a predictive enhancement of speech intelligibility.

Speech perception may be underpinned by a hierarchical cortical system, which attempts to match "external" incoming sensory inputs with "internal" top-down predictions. Prior knowledge modulates internal predictions of an upcoming stimulus and exerts its effects in temporal and inferior frontal cortex. Here, we used source-space magnetoencephalography (MEG) to study the spatiotemporal dynamics underpinning the integration of prior knowledge in the speech processing network. Prior knowledge was manipulated to i) increase the perceived intelligibility of speech sentences, and ii) dissociate the perceptual effects of changes in speech intelligibility from acoustical differences in speech stimuli. Cortical entrainment to the speech temporal envelope, which accounts for neural activity specifically related to sensory information, was affected by prior knowledge: This effect emerged early (∼50 ms) in left inferior frontal gyrus (IFG) and then (∼100 ms) in Heschl's gyrus (HG), and was sustained until latencies of ∼250 ms. Directed transfer function (DTF) measures were used for estimating direct Granger causal relations between locations of interest. In line with the cortical entrainment result, this analysis indicated that prior knowledge enhanced top-down connections from left IFG to all the left temporal areas of interest - namely HG, superior temporal sulcus (STS), and middle temporal gyrus (MTG). In addition, intelligible speech increased top-down information flow between left STS and left HG, and increased bottom-up flow in higher-order temporal cortex, specifically between STS and MTG. These results are compatible with theories that explain this mechanism as a result of both ascending and descending cortical interactions, such as predictive coding. Altogether, this study provides a detailed view of how, where and when prior knowledge influences continuous speech perception.

Anterior paracingulate and cingulate cortex mediates the effects of cognitive load on speech sound discrimination.

Perceiving speech while performing another task is a common challenge in everyday life. How the brain controls resource allocation during speech perception remains poorly understood. Using functional magnetic resonance imaging (fMRI), we investigated the effect of cognitive load on speech perception by examining brain responses of participants performing a phoneme discrimination task and a visual working memory task simultaneously. The visual task involved holding either a single meaningless image in working memory (low cognitive load) or four different images (high cognitive load). Performing the speech task under high load, compared to low load, resulted in decreased activity in pSTG/pMTG and increased activity in visual occipital cortex and two regions known to contribute to visual attention regulation-the superior parietal lobule (SPL) and the paracingulate and anterior cingulate gyrus (PaCG, ACG). Critically, activity in PaCG/ACG was correlated with performance in the visual task and with activity in pSTG/pMTG: Increased activity in PaCG/ACG was observed for individuals with poorer visual performance and with decreased activity in pSTG/pMTG. Moreover, activity in a pSTG/pMTG seed region showed psychophysiological interactions with areas of the PaCG/ACG, with stronger interaction in the high-load than the low-load condition. These findings show that the acoustic analysis of speech is affected by the demands of a concurrent visual task and that the PaCG/ACG plays a role in allocating cognitive resources to concurrent auditory and visual information.

Early Activity in Broca's Area During Reading Reflects Fast Access to Articulatory Codes From Print.

Prior evidence for early activity in Broca's area during reading may reflect fast access to articulatory codes in left inferior frontal gyrus pars opercularis (LIFGpo). We put this hypothesis to test using a benchmark for articulatory involvement in reading known as the masked onset priming effect (MOPE). In masked onset priming, briefly presented pronounceable strings of letters that share an initial phoneme with subsequently presented target words (e.g., gilp-GAME) facilitate word naming responses compared with unrelated primes (dilp-GAME). Crucially, these priming effects only occur when the task requires articulation (naming), and not when it requires lexical decisions. A standard explanation of masked onset priming is that it reflects fast computation of articulatory output codes from letter representations. We therefore predicted 1) that activity in left IFG pars opercularis would be modulated by masked onset priming, 2) that priming-related modulation in LIFGpo would immediately follow activity in occipital cortex, and 3) that this modulation would be greater for naming than for lexical decision. These predictions were confirmed in a magnetoencephalography (MEG) priming study. MOPEs emerged in left IFG at ∼100 ms posttarget onset, and the priming effects were more sustained when the task involved articulation.

The role of phase-locking to the temporal envelope of speech in auditory perception and speech intelligibility.

The temporal envelope of speech is important for speech intelligibility. Entrainment of cortical oscillations to the speech temporal envelope is a putative mechanism underlying speech intelligibility. Here we used magnetoencephalography (MEG) to test the hypothesis that phase-locking to the speech temporal envelope is enhanced for intelligible compared with unintelligible speech sentences. Perceptual "pop-out" was used to change the percept of physically identical tone-vocoded speech sentences from unintelligible to intelligible. The use of pop-out dissociates changes in phase-locking to the speech temporal envelope arising from acoustical differences between un/intelligible speech from changes in speech intelligibility itself. Novel and bespoke whole-head beamforming analyses, based on significant cross-correlation between the temporal envelopes of the speech stimuli and phase-locked neural activity, were used to localize neural sources that track the speech temporal envelope of both intelligible and unintelligible speech. Location-of-interest analyses were carried out in a priori defined locations to measure the representation of the speech temporal envelope for both un/intelligible speech in both the time domain (cross-correlation) and frequency domain (coherence). Whole-brain beamforming analyses identified neural sources phase-locked to the temporal envelopes of both unintelligible and intelligible speech sentences. Crucially there was no difference in phase-locking to the temporal envelope of speech in the pop-out condition in either the whole-brain or location-of-interest analyses, demonstrating that phase-locking to the speech temporal envelope is not enhanced by linguistic information.

Neural mechanisms underlying song and speech perception can be differentiated using an illusory percept.

The issue of whether human perception of speech and song recruits integrated or dissociated neural systems is contentious. This issue is difficult to address directly since these stimulus classes differ in their physical attributes. We therefore used a compelling illusion (Deutsch et al. 2011) in which acoustically identical auditory stimuli are perceived as either speech or song. Deutsch's illusion was used in a functional MRI experiment to provide a direct, within-subject investigation of the brain regions involved in the perceptual transformation from speech into song, independent of the physical characteristics of the presented stimuli. An overall differential effect resulting from the perception of song compared with that of speech was revealed in right midposterior superior temporal sulcus/right middle temporal gyrus. A left frontotemporal network, previously implicated in higher-level cognitive analyses of music and speech, was found to co-vary with a behavioural measure of the subjective vividness of the illusion, and this effect was driven by the illusory transformation. These findings provide evidence that illusory song perception is instantiated by a network of brain regions that are predominantly shared with the speech perception network.

Divergent effects of listening demands and evaluative threat on listening effort in online and laboratory settings.

Objective: Listening effort (LE) varies as a function of listening demands, motivation and resource availability, among other things. Motivation is posited to have a greater influence on listening effort under high, compared to low, listening demands. Methods: To test this prediction, we manipulated the listening demands of a speech recognition task using tone vocoders to create moderate and high listening demand conditions. We manipulated motivation using evaluative threat, i.e., informing participants that they must reach a particular "score" for their results to be usable. Resource availability was assessed by means of working memory span and included as a fixed effects predictor. Outcome measures were indices of LE, including reaction times (RTs), self-rated work and self-rated tiredness, in addition to task performance (correct response rates). Given the recent popularity of online studies, we also wanted to examine the effect of experimental context (online vs. laboratory) on the efficacy of manipulations of listening demands and motivation. We carried out two highly similar experiments with two groups of 37 young adults, a laboratory experiment and an online experiment. To make listening demands comparable between the two studies, vocoder settings had to differ. All results were analysed using linear mixed models. Results: Results showed that under laboratory conditions, listening demands affected all outcomes, with significantly lower correct response rates, slower RTs and greater self-rated work with higher listening demands. In the online study, listening demands only affected RTs. In addition, motivation affected self-rated work. Resource availability was only a significant predictor for RTs in the online study. Discussion: These results show that the influence of motivation and listening demands on LE depends on the type of outcome measures used and the experimental context. It may also depend on the exact vocoder settings. A controlled laboratory settings and/or particular vocoder settings may be necessary to observe all expected effects of listening demands and motivation.

Representations of the temporal envelope of sounds in human auditory cortex: can the results from invasive intracortical "depth" electrode recordings be replicated using non-invasive MEG "virtual electrodes"?

Magnetoencephalography (MEG) beamformer analyses use spatial filters to estimate neuronal activity underlying the magnetic fields measured by the MEG sensors. MEG "virtual electrodes" are the outputs of beamformer spatial filters. The present study aimed to test the hypothesis that MEG virtual electrodes can replicate the findings from intracortical "depth" electrode studies relevant to the processing of the temporal envelopes of sounds [e.g. Nourski et al. (2009) "Temporal envelope of time-compressed speech represented in the human auditory cortex," J. Neurosci. 29:15564-15574]. Specifically we aimed to determine whether it is possible to use non-invasive MEG virtual electrodes to characterise the representation of temporal envelopes of 6-Hz sinusoidal amplitude modulation (SAM) and speech using both auditory evoked fields (AEFs) and patterns of power changes in high-frequency (>70 Hz) bands. MEG signals were analysed using a location of interest (LOI) approach by seeding virtual electrodes in the left and right posteromedial Heschl's gyri. AEFs showed phase-locking to the temporal envelope of SAM and speech stimuli. Time-frequency analyses revealed no clear differences in high gamma power between the pre-stimulus baseline and the post-stimulus presentation periods. Nevertheless the patterns of changes in high gamma power were significantly correlated with the temporal envelopes of 6-Hz SAM and speech in the majority of participants. The present study reveals difficulties in replicating clear augmentations in high gamma power changes using MEG virtual electrodes cf. intracortical "depth" electrode studies (Nourski et al., 2009).

"We're just winging it". Identifying targets for intervention to improve the provision of hearing support for residents living with dementia in long-term care: an interview study with care staff.

PURPOSE: Hearing loss and dementia are common in long-term care home (LTCH) residents, causing communication difficulties and worsened behavioural symptoms. Hearing support provided to residents with dementia requires improvement. This study is the first to use the Behaviour Change Wheel (BCW) to identify barriers and propose interventions to improve the provision of hearing support by LTCH staff. METHODS: Semi-structured interviews with 10 staff members were conducted. Transcripts were analysed according to the BCW's Theoretical Domains Framework alongside reflective thematic analysis. Relevant intervention functions and exemplar interventions were proposed. RESULTS: Staff believed hearing support to be beneficial to residents (Beliefs about Consequences) but lacked knowledge of hearing loss management (Knowledge). Poor collaborations between LTCHs and audiology (Environmental Context and Resources), led to despondency, and apprehension about traditional hearing aids for residents (Optimism). Despite feeling responsible for hearing support, staff lacked personal accountability (Social/Professional Role and Identity). CONCLUSIONS: Future interventions should include staff Training (on hearing support), Education (on the consequences of unsupported hearing loss), Enablement (dementia-friendly hearing devices), Incentivisation and Modelling (of Hearing Champions) and Environmental Restructuring (flexible audiology appointments to take place within the LTCH). Interventions should be multi-faceted to boost the capabilities, opportunities and motivations of LTCH staff.

Hearing support for care home residents with dementia:Long-term care staff report inadequate knowledge and awareness of how to support residents' hearing needs and a lack of personal accountability for providing hearing support.They also report poor collaborations with audiologists and apprehension about traditional hearing aids.Barriers to hearing support stem from gaps in the capabilities, opportunities and motivations of staff, therefore, interventions should be designed to target all three constructs.Interventions to aid hearing support provision should target staffs' education, training, enablement, persuasion, modelling, incentivisation and environmental restructuring to boost staff capabilities, opportunities and motivations to provide hearing support.

Quantifying the Effects of Motivation on Listening Effort: A Systematic Review and Meta-Analysis.

Motivation influences the amount of listening effort (LE) exerted or experienced under challenging conditions, such as in high-noise environments. This systematic review and meta-analysis is the first to quantify the effects of motivation on LE. The review was pre-registered in PROSPERO, and performed in accordance with PRISMA guidelines. Eligible studies examined the influence of motivation or individual traits (related to motivation) on LE in adults. Motivational factors, coded as independent variables, included financial reward, evaluative threat, perceived competence, feedback, and individual traits. LE outcomes were categorized as subjective, behavioral, or physiological. The quality of evidence was assessed using an adaptation of the Cochrane Collaboration Risk of Bias Tool. Nested random-effects meta-analyses were performed to quantify and compare the influence of motivational factors across LE outcomes. After assessing 3,532 records, 48 studies met the inclusion criteria and 43 were included in the meta-analyses. Risk of bias was high, for example, many studies lacked sample size justification. Motivational factors had a small-to-medium effect (mean Cohen's d = 0.34, range: 0.11-0.72) on LE. When LE outcomes were considered collectively, an external manipulation of motivation (perceived competence) produced a larger mean effect size compared with individual traits. Some combinations of motivational factors and LE outcomes produced more robust effects than others, for example, evaluative threat and subjective LE outcomes. Although wide prediction intervals and high risk of bias mean that significant positive effects cannot be guaranteed, these findings provide useful guidance on the selection of motivational factors and LE outcomes for future research.

Effectiveness of Hearing Rehabilitation for Care Home Residents With Dementia: A Systematic Review.

OBJECTIVES: To report the effectiveness of, and barriers and facilitators to, hearing rehabilitation for care home residents with dementia. DESIGN: Systematic review. SETTING AND PARTICIPANTS: Care home residents with dementia and hearing loss. METHODS: No restrictions on publication date or language were set and gray literature was considered. Eligible studies were critically appraised and presented via a narrative review. RESULTS: Sixteen studies, most of low to moderate quality, were identified. Hearing rehabilitation, including hearing devices, communication techniques, and visual aids (eg, flashcards), was reported to improve residents' communication and quality of life and reduce agitation, with improvements in staff knowledge of hearing loss and job satisfaction. Residents' symptoms of dementia presented barriers, for example, losing or not tolerating hearing aids. Low staff prioritization of hearing loss due to time pressures and lack of hearing-related training for staff were further barriers, particularly for residents who required assistance with hearing devices. Adopting a person-centered approach based on residents' capabilities and preferences and involving family members facilitated hearing device use. CONCLUSIONS AND IMPLICATIONS: Residents with dementia can benefit from hearing rehabilitation. Identifying and implementing efficient, individualized hearing rehabilitation is necessary for those with complex cognitive needs. Increased funding and support for the social care sector is required to address systemic issues that pose barriers to hearing rehabilitation, including time pressures, lack of training for staff and access to audiology services for residents.

Functional asymmetries in the representation of noise-vocoded speech.

It is generally accepted that, while speech is processed bilaterally in auditory cortical areas, complementary analyses of the speech signal are carried out across the hemispheres. However, the Asymmetric Sampling in Time (AST) model (Poeppel, 2003) suggests that there is functional asymmetry due to different time scales of temporal integration in each hemisphere. The right hemisphere preferentially processes slow modulations commensurate with the theta frequency band (~4-8 Hz), whereas the left hemisphere is more sensitive to fast temporal modulations in the gamma frequency range (~25-50 Hz). Here we examined the perception of noise-vocoded, i.e. spectrally-degraded, words. Magnetoencephalography (MEG) beamformer analyses were used to determine where and how noise-vocoded speech is represented in terms of changes in power resulting from neuronal activity. The outputs of beamformer spatial filters were used to delineate the temporal dynamics of these changes in power. Beamformer analyses localised low-frequency "delta" (1-4 Hz) and "theta" (3-6 Hz) changes in total power to the left hemisphere and high-frequency "gamma" (60-80 Hz, 80-100 Hz) changes in total power to the right hemisphere. Time-frequency analyses confirmed the frequency content and timing of changes in power in the left and right hemispheres. Together the beamformer and time-frequency analyses demonstrate a functional asymmetry in the representation of noise-vocoded words that is inconsistent with the AST model, at least in brain areas outside of primary auditory cortex.

On the mechanisms involved in the recovery of envelope information from temporal fine structure.

Three experiments were designed to provide psychophysical evidence for the existence of envelope information in the temporal fine structure (TFS) of stimuli that were originally amplitude modulated (AM). The original stimuli typically consisted of the sum of a sinusoidally AM tone and two unmodulated tones so that the envelope and TFS could be determined a priori. Experiment 1 showed that normal-hearing listeners not only perceive AM when presented with the Hilbert fine structure alone but AM detection thresholds are lower than those observed when presenting the original stimuli. Based on our analysis, envelope recovery resulted from the failure of the decomposition process to remove the spectral components related to the original envelope from the TFS and the introduction of spectral components related to the original envelope, suggesting that frequency- to amplitude-modulation conversion is not necessary to recover envelope information from TFS. Experiment 2 suggested that these spectral components interact in such a way that envelope fluctuations are minimized in the broadband TFS. Experiment 3 demonstrated that the modulation depth at the original carrier frequency is only slightly reduced compared to the depth of the original modulator. It also indicated that envelope recovery is not specific to the Hilbert decomposition.

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 Hotelling's 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 Hotelling's 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.