Publications by authors named "Jan Wouters"

218 Publications

Enhanced neural tracking of the fundamental frequency of the voice.

IEEE Trans Biomed Eng 2021 May 13;PP. Epub 2021 May 13.

Objective: 'F0 tracking' is a novel method that investigates neural processing of the fundamental frequency of the voice (f0) in continuous speech. Using linear modelling, a feature that reflects the f0 of a presented speech stimulus is predicted from neural EEG responses. The correlation between the predicted and the 'actual' f0 feature is a measure for neural response strength. In this study, we aimed to design a new f0 feature that approximates the expected human EEG response to the f0 in order to improve neural tracking results.

Methods: Two techniques were explored: constructing the feature with a phenomenological model to simulate neural processing in the auditory periphery and low-pass filtering the feature to approximate the effect of more central processing.

Results: Analysis of EEG-data evoked by a Flemish story in 34 subjects indicated that both the auditory model and the low-pass filter significantly improved the correlations between the actual and reconstructed feature. The combination of both strategies almost doubled the mean correlation across subjects, from 0.078 to 0.13. Moreover, canonical correlation analysis revealed two distinct processes contributing to the f0 response: one driven by broad range of auditory nerve fibers with center frequency up to 8 kHz and one driven by a more narrow selection of auditory nerve fibers, possibly responding to unresolved harmonics.

Conclusion: Optimizing the f0 feature towards the expected neural response, significantly improves f0-tracking correlations.

Significance: The optimized f0 feature enhances the f0-tracking method, facilitating future research on temporal auditory processing in the human brain.
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http://dx.doi.org/10.1109/TBME.2021.3080123DOI Listing
May 2021

A three-time point longitudinal investigation of the arcuate fasciculus throughout reading acquisition in children developing dyslexia.

Neuroimage 2021 Apr 17:118087. Epub 2021 Apr 17.

Parenting and Special Education Research Unit, Faculty of Psychology and Educational Sciences, KU Leuven, Belgium; Research Group ExpORL, Department of Neurosciences, KU Leuven, Belgium; Psychological Sciences Research Institute, Université Catholique de Louvain, Louvain-la-Neuve, Belgium; Institute of Neuroscience, Université Catholique de Louvain, 1348 Louvain-la-Neuve, Belgium. Electronic address:

Although the neural basis of dyslexia has intensively been investigated, results are still unclear about the existence of a white matter deficit in the arcuate fasciculus (AF) throughout development. To unravel this ambiguity, we examined the difference in fractional anisotropy (FA) of the AF between children developing dyslexia and children developing typical reading skills in a longitudinal sample with three MRI time points throughout reading development: the pre-reading stage (5-6 years old), the early reading stage (7-8 years old) and the advanced reading stage (9-10 years old). Applying along-the-tract analyses of white matter organization, our results confirmed that a white matter deficit existed in the left AF prior to the onset of formal reading instruction in children who developed dyslexia later on. This deficit was consistently present throughout the course of reading development. Additionally, we evaluated the use of applying a continuous approach on the participants' reading skills rather than the arbitrary categorization in individuals with or without dyslexia. Our results confirmed the predictive relation between FA and word reading measurements later in development. This study supports the use of longitudinal approaches to investigate the neural basis of the developmental process of learning to read and the application of triangulation, i.e. using multiple research approaches to help gain more insight and aiding the interpretation of obtained results.
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http://dx.doi.org/10.1016/j.neuroimage.2021.118087DOI Listing
April 2021

Neural tracking of the fundamental frequency of the voice: The effect of voice characteristics.

Eur J Neurosci 2021 Apr 16. Epub 2021 Apr 16.

ExpORL, Department of Neurosciences, KU Leuven, Leuven, Belgium.

Traditional electrophysiological methods to study temporal auditory processing of the fundamental frequency of the voice (f0) often use unnaturally repetitive stimuli. In this study, we investigated f0 processing of meaningful continuous speech. EEG responses evoked by stories in quiet were analysed with a novel method based on linear modelling that characterizes the neural tracking of the f0. We studied both the strength and the spatio-temporal properties of the f0-tracking response. Moreover, different samples of continuous speech (six stories by four speakers: two male and two female) were used to investigate the effect of voice characteristics on the f0 response. The results indicated that response strength is inversely related to f0 frequency and rate of f0 change throughout the story. As a result, the male-narrated stories in this study (low and steady f0) evoked stronger f0-tracking compared to female-narrated stories (high and variable f0), for which many responses were not significant. The spatio-temporal analysis revealed that f0-tracking response generators were not fixed in the brainstem but were voice-dependent as well. Voices with high and variable f0 evoked subcortically dominated responses with a latency between 7 and 12 ms. Voices with low and steady f0 evoked responses that are both subcortically (latency of 13-15 ms) and cortically (latency of 23-26 ms) generated, with the right primary auditory cortex as a likely cortical source. Finally, additional experiments revealed that response strength greatly improves for voices with strong higher harmonics, which is particularly useful to boost the small responses evoked by voices with high f0.
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http://dx.doi.org/10.1111/ejn.15229DOI Listing
April 2021

A Bridge over Troubled Listening: Improving Speech-in-Noise Perception by Children with Dyslexia.

J Assoc Res Otolaryngol 2021 Apr 16. Epub 2021 Apr 16.

Department of Neurosciences, Research Group Experimental ORL, KU Leuven University of Leuven, Leuven, Belgium.

Developmental dyslexia is most commonly associated with phonological processing difficulties. However, children with dyslexia may experience poor speech-in-noise perception as well. Although there is an ongoing debate whether a speech perception deficit is inherent to dyslexia or acts as an aggravating risk factor compromising learning to read indirectly, improving speech perception might boost reading-related skills and reading acquisition. In the current study, we evaluated advanced speech technology as applied in auditory prostheses, to promote and eventually normalize speech perception of school-aged children with dyslexia, i.e., envelope enhancement (EE). The EE strategy automatically detects and emphasizes onset cues and consequently reinforces the temporal structure of the speech envelope. Our results confirmed speech-in-noise perception difficulties by children with dyslexia. However, we found that exaggerating temporal "landmarks" of the speech envelope (i.e., amplitude rise time and modulations)-by using EE-passively and instantaneously improved speech perception in noise for children with dyslexia. Moreover, the benefit derived from EE was large enough to completely bridge the initial gap between children with dyslexia and their typical reading peers. Taken together, the beneficial outcome of EE suggests an important contribution of the temporal structure of the envelope to speech perception in noise difficulties in dyslexia, providing an interesting foundation for future intervention studies based on auditory and speech rhythm training.
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http://dx.doi.org/10.1007/s10162-021-00793-4DOI Listing
April 2021

The digit triplet test: a scoping review.

Int J Audiol 2021 Apr 11:1-18. Epub 2021 Apr 11.

Department of Neurosciences, Research Group ExpORL, KU Leuven, Leuven, Belgium.

Objective: This review article presents an overview of all Digit Triplet Tests (DTT) and digits-in-noise tests (DIN) and their variations in language, speech material, masking noise, test procedures, and targeted population. The effects on aspects of validity, reliability, and feasibility are investigated.

Design: Scoping review.

Study Sample: All studies referring to the DTT and DIN were collected from Pubmed and Embase. Search terms "digit triplet test" and "digits in noise" were used. Citations of selected articles were scanned backwards in time (the bibliography of the already selected research article) and forward in time (articles that cited the already selected research article). The search terms yielded 95 results in total. Eventually, 39 papers were selected.

Results: Analyses showed psychometric reference-curves with steep slopes and speech reception thresholds with high measurement precision which are strongly associated with pure tone audiometry. High sensitivity and specificity to detect elevated pure tone thresholds were noted for test variants. Certain procedural modifications of the DTT and DIN can further improve the test. Additionally, large-scale application of the DTT and DIN is feasible.

Conclusion: The DTT and DIN are a very valuable tool for screening and diagnostics for a wide variety of populations.
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http://dx.doi.org/10.1080/14992027.2021.1902579DOI Listing
April 2021

The identification of predominant auditory steady-state response brain sources in electroencephalography using denoising source separation.

Eur J Neurosci 2021 Apr 2. Epub 2021 Apr 2.

Research Group Experimental ORL, Department of Neurosciences, KU Leuven-University of Leuven, Leuven, Belgium.

Different approaches have been used to extract auditory steady-state responses (ASSRs) from electroencephalography (EEG) recordings, including region-related electrode configurations (electrode level) and the manual placement of equivalent current dipoles (source level). Inherent limitations of these approaches are the assumption of the anatomical origin and the omission of activity generated by secondary sources. Data-driven methods such as independent component analysis (ICA) seem to avoid these limitations but only to face new others such as the presence of ASSRs with similar properties in different components and the manual selection protocol to select and classify the most relevant components carrying ASSRs. We propose the novel approach of applying a spatial filter to these components in order to extract the most relevant information. We aimed to develop a method based on the reproducibility across trials that performs reliably in low-signal-to-noise ratio (SNR) scenarios using denoising source separation (DSS). DSS combined with ICA successfully reduced the number of components and extracted the most relevant ASSR at 4, 10 and 20 Hz stimulation in group and individual level studies of EEG adolescent data. The anatomical brain location for these low stimulation frequencies showed results in cortical areas with relatively small dispersion. However, for 40 and 80 Hz, results with regard to the number of components and the anatomical origin were less clear. At all stimulation frequencies the outcome measures were consistent with literature, and the partial rejection of inter-subject variability led to more accurate results and higher SNRs. These findings are promising for future applications in group comparison involving pathologies.
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http://dx.doi.org/10.1111/ejn.15219DOI Listing
April 2021

Frequency following responses and rate change complexes in cochlear implant users.

Hear Res 2021 May 11;404:108200. Epub 2021 Feb 11.

KU Leuven, Department of Neurosciences, ExpORL, Herestraat 49, Box 721, Leuven 3000, Belgium.

The upper limit of rate-based pitch perception and rate discrimination can differ substantially across cochlear implant (CI) users. One potential reason for this difference is the presence of a biological limitation on temporal encoding in the electrically-stimulated auditory pathway, which can be inherent to the electrical stimulation itself and/or to the degenerative processes associated with hearing loss. Electrophysiological measures, like the electrically-evoked frequency following response (eFFR) and auditory change complex (eACC), could potentially provide valuable insights in the temporal processing limitations at the level of the brainstem and cortex in the electrically-stimulated auditory pathway. Obtaining these neural responses, free from stimulation artifacts, is challenging, especially when the neural response is phase-locked to the stimulation rate, as is the case for the eFFR. In this study we investigated the feasibility of measuring eFFRs, free from stimulation artifacts, to stimulation rates ranging from 94 to 196 pulses per second (pps) and eACCs to pulse rate changes ranging from 36 to 108%, when stimulating in a monopolar configuration. A high-sampling rate EEG system was used to measure the electrophysiological responses in five CI users, and linear interpolation was applied to remove the stimulation artifacts from the EEG. With this approach, we were able to measure eFFRs for pulse rates up to 162 pps and eACCs to the different rate changes. Our results show that it is feasible to measure electrophysiological responses, free from stimulation artifacts, that could potentially be used as neural correlates for rate and pitch processing in CI users.
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http://dx.doi.org/10.1016/j.heares.2021.108200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8052190PMC
May 2021

Using Interleaved Stimulation to Measure the Size and Selectivity of the Sustained Phase-Locked Neural Response to Cochlear Implant Stimulation.

J Assoc Res Otolaryngol 2021 Apr 25;22(2):141-159. Epub 2021 Jan 25.

Cambridge Hearing Group, Dept. Clinical Neurosciences, University of Cambridge, Cambridge Biomedical Campus, Cambridge, CB2 0QQ, England.

We measured the sustained neural response to electrical stimulation by a cochlear implant (CI). To do so, we interleaved two stimuli with frequencies F1 and F2 Hz and recorded a neural distortion response (NDR) at F2-F1 Hz. We show that, because any one time point contains only the F1 or F2 stimulus, the instantaneous nonlinearities typical of electrical artefact should not produce distortion at this frequency. However, if the stimulus is smoothed, such as by charge integration at the nerve membrane, subsequent (neural) nonlinearities can produce a component at F2-F1 Hz. We stimulated a single CI electrode with interleaved sinusoids or interleaved amplitude-modulated pulse trains such that F2 = 1.5F1, and found no evidence for an NDR when F2-F1 was between 90 and 120 Hz. However, interleaved amplitude-modulated pulse trains with F2-F1~40 Hz revealed a substantial NDR with a group delay of about 45 ms, consistent with a thalamic and/or cortical response. The NDR could be measured even from recording electrodes adjacent to the implant and at the highest pulse rates (> 4000 pps) used clinically. We then measured the selectivity of this sustained response by presenting F1 and F2 to different electrodes and at different between-electrode distances. This revealed a broad tuning that, we argue, reflects the overlap between the excitation elicited by the two electrodes. Our results also provide a glimpse of the neural nonlinearity in the auditory system, unaffected by the biomechanical cochlear nonlinearities that accompany acoustic stimulation. Several potential clinical applications of our findings are discussed.
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http://dx.doi.org/10.1007/s10162-020-00783-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7943679PMC
April 2021

Stimulus-evoked phase-locked activity along the human auditory pathway strongly varies across individuals.

Sci Rep 2021 Jan 8;11(1):143. Epub 2021 Jan 8.

Research Group Experimental Oto-rhino-laryngology (ExpORL), Department of Neurosciences, KU Leuven, Herestraat 49, Box 721, 3000, Leuven, Belgium.

Phase-locking to the temporal envelope of speech is associated with envelope processing and speech perception. The phase-locked activity of the auditory pathway, across modulation frequencies, is generally assessed at group level and shows a decrease in response magnitude with increasing modulation frequency. With the exception of increased activity around 40 and 80 to 100 Hz. Furthermore, little is known about the phase-locked response patterns to modulation frequencies ≤ 20 Hz, which are modulations predominately present in the speech envelope. In the present study we assess the temporal modulation transfer function (TMTF) of the phase-locked activity of the auditory pathway, from 0.5 to 100 Hz at a high-resolution and by means of auditory steady-state responses. Although the group-averaged TMTF corresponds well with those reported in the literature, the individual TMTF shows a remarkable intersubject variability. This intersubject variability is especially present for ASSRs that originate from the cortex and are evoked with modulation frequencies ≤ 20 Hz. Moreover, we found that these cortical phase-locked activity patterns are robust over time. These results show the importance of the individual TMTF when assessing phase-locked activity to envelope fluctuations, which can potentially be used as a marker for auditory processing.
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http://dx.doi.org/10.1038/s41598-020-80229-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7794304PMC
January 2021

Neural Generators Underlying Temporal Envelope Processing Show Altered Responses and Hemispheric Asymmetry Across Age.

Front Aging Neurosci 2020 4;12:596551. Epub 2020 Dec 4.

Research Group Experimental Oto-rhino-laryngology (ExpORL), Department of Neurosciences, Katholieke Universiteit Leuven, Leuven, Belgium.

Speech understanding problems are highly prevalent in the aging population, even when hearing sensitivity is clinically normal. These difficulties are attributed to changes in central temporal processing with age and can potentially be captured by age-related changes in neural generators. The aim of this study is to investigate age-related changes in a wide range of neural generators during temporal processing in middle-aged and older persons with normal audiometric thresholds. A minimum-norm imaging technique is employed to reconstruct cortical and subcortical neural generators of temporal processing for different acoustic modulations. The results indicate that for relatively slow modulations (<50 Hz), the response strength of neural sources is higher in older adults than in younger ones, while the phase-locking does not change. For faster modulations (80 Hz), both the response strength and the phase-locking of neural sources are reduced in older adults compared to younger ones. These age-related changes in temporal envelope processing of slow and fast acoustic modulations are possibly due to loss of functional inhibition, which is accompanied by aging. Both cortical (primary and non-primary) and subcortical neural generators demonstrate similar age-related changes in response strength and phase-locking. Hemispheric asymmetry is also altered in older adults compared to younger ones. Alterations depend on the modulation frequency and side of stimulation. The current findings at source level could have important implications for the understanding of age-related changes in auditory temporal processing and for developing advanced rehabilitation strategies to address speech understanding difficulties in the aging population.
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http://dx.doi.org/10.3389/fnagi.2020.596551DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7746817PMC
December 2020

Brain mapping of auditory steady-state responses: A broad view of cortical and subcortical sources.

Hum Brain Mapp 2021 Feb 9;42(3):780-796. Epub 2020 Nov 9.

Research Group Experimental ORL, Department of Neurosciences, Katholieke Universiteit Leuven, Leuven, Belgium.

Auditory steady-state responses (ASSRs) are evoked brain responses to modulated or repetitive acoustic stimuli. Investigating the underlying neural generators of ASSRs is important to gain in-depth insight into the mechanisms of auditory temporal processing. The aim of this study is to reconstruct an extensive range of neural generators, that is, cortical and subcortical, as well as primary and non-primary ones. This extensive overview of neural generators provides an appropriate basis for studying functional connectivity. To this end, a minimum-norm imaging (MNI) technique is employed. We also present a novel extension to MNI which facilitates source analysis by quantifying the ASSR for each dipole. Results demonstrate that the proposed MNI approach is successful in reconstructing sources located both within (primary) and outside (non-primary) of the auditory cortex (AC). Primary sources are detected in different stimulation conditions (four modulation frequencies and two sides of stimulation), thereby demonstrating the robustness of the approach. This study is one of the first investigations to identify non-primary sources. Moreover, we show that the MNI approach is also capable of reconstructing the subcortical activities of ASSRs. Finally, the results obtained using the MNI approach outperform the group-independent component analysis method on the same data, in terms of detection of sources in the AC, reconstructing the subcortical activities and reducing computational load.
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http://dx.doi.org/10.1002/hbm.25262DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7814770PMC
February 2021

The relation between neurofunctional and neurostructural determinants of phonological processing in pre-readers.

Dev Cogn Neurosci 2020 12 20;46:100874. Epub 2020 Oct 20.

Research Group Experimental ORL, Department of Neurosciences, KU Leuven - University of Leuven, Herestraat 49 Box 721, B-3000 Leuven, Belgium.

Phonological processing skills are known as the most robust cognitive predictor of reading ability. Therefore, the neural determinants of phonological processing have been extensively investigated by means of either neurofunctional or neurostructural techniques. However, to fully understand how the brain represents and processes phonological information, there is need for studies that combine both methods. The present study applies such a multimodal approach with the aim of investigating the pre-reading relation between neural measures of auditory temporal processing, white matter properties of the reading network and phonological processing skills. We administered auditory steady-state responses, diffusion-weighted MRI scans and phonological awareness tasks in 59 pre-readers. Our results demonstrate that a stronger rightward lateralization of syllable-rate (4 Hz) processing coheres with higher fractional anisotropy in the left fronto-temporoparietal arcuate fasciculus. Both neural features each in turn relate to better phonological processing skills. As such, the current study provides novel evidence for the existence of a pre-reading relation between functional measures of syllable-rate processing, structural organization of the arcuate fasciculus and cognitive precursors of reading development. Moreover, our findings demonstrate the value of combining different neural techniques to gain insight in the underlying neural systems for reading (dis)ability.
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http://dx.doi.org/10.1016/j.dcn.2020.100874DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7606842PMC
December 2020

Pre-literacy heterogeneity in Dutch-speaking kindergartners: latent profile analysis.

Ann Dyslexia 2020 10 19;70(3):275-294. Epub 2020 Oct 19.

Parenting and Special Education Research Unit, Faculty of Psychology and Educational Sciences, KU Leuven, Leuven, Belgium.

Research demonstrated that a dyslexia diagnosis is mainly given after the most effective time for intervention has passed, referred to as the dyslexia paradox. Although some pre-reading cognitive measures have been found to be strong predictors of early literacy acquisition, i.e., phonological awareness (PA), letter knowledge (LK), and rapid automatized naming (RAN), more insight in the variability of pre-reading profiles might be of great importance for early identification of children who have an elevated risk for developing dyslexia and to provide tailor-made interventions. To address this issue, this study used a latent profile analysis (LPA) to disentangle different pre-reading profiles in a sample of 1091 Dutch-speaking kindergartners. Four profiles emerged: high performers (16.50%), average performers (40.24%), below-average performers with average IQ (25.57%), and below-average performers with below-average IQ (17.69%). These results suggested two at-risk profiles diverging in IQ, which are presumably more likely to develop dyslexia later on. Although below-average profiles differed significantly in rapid naming and IQ, no clear evidence for the double-deficit theory was found in Dutch-speaking kindergartners. Educational level and reading history of the parents appeared to be predictive for children's classification membership. Our results point towards the heterogeneity that is already present in kindergartners and the possibility to identify at-risk profiles prior to reading instruction, which may be the foundation for earlier targeted interventions. However, more extended research is needed to determine the stability of these profiles across time and across different languages.
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http://dx.doi.org/10.1007/s11881-020-00207-9DOI Listing
October 2020

The Cost of Intrinsic and Extrinsic Cognitive Demands on Auditory Functioning in Older Adults With Normal Hearing or Using Hearing Aids.

Ear Hear 2020 Oct 6;42(3):615-628. Epub 2020 Oct 6.

Department of Neurosciences, KU Leuven - University of Leuven, ExpORL, Leuven, Belgium.

Objectives: We investigated the impact of both intrinsic and extrinsic cognitive demands on auditory and secondary task performance in older adults with normal hearing (NH) and adults using hearing aids (HAs) in an ecologically relevant listening environment.

Design: Fifteen adults with NH and 15 adults using HAs (60 to 72 years of age) were recruited to perform the "Audiovisual True-to-Life Assessment of Auditory Rehabilitation"-paradigm (AVATAR), which combines an auditory-visual speech-in-noise task with three secondary tasks on either auditory localization or visual short-term memory in a preload multitask paradigm. Intrinsic demands were altered by presenting speech either at equivalent speech accuracy levels of 50% correct (SPIN50%) or equivalent speech-to-noise ratios of +5dB SNR (SPIN+5dB). We manipulated the amount of extrinsic cognitive demands by including one (dual condition) or three secondary tasks (quadruple condition). Performance decrements on the secondary tasks were considered to reflect an increase in resource allocation to speech understanding and thus an increase in listening effort. In addition, we administered a cognitive test battery as well as a questionnaire on self-reported hearing difficulties and subjective measures of effort and motivation.

Results: Speech understanding and secondary task performance on the visual short-term memory task were lower in the SPIN50% condition compared to SPIN+5dB. Whereas speech understanding at SPIN50% was equally high in the dual and quadruple conditions, the quadruple condition resulted in lower secondary task performance on the visual short-term memory task, higher levels of self-reported effort, and lower motivation compared to the dual-task condition. The same was true for experimental conditions at SPIN+5dB. Additionally, adults with NH outperformed adults using HAs on speech understanding, auditory localization, and self-reported hearing abilities, but no group differences were observed on secondary task costs or cognitive measures.

Conclusions: This study showed that, irrespective of the hearing status of the listener, speech performance was not affected by the amount of extrinsic cognitive demands, but was worse and required more effort under conditions with a more negative SNR. Also, increasing the extrinsic cognitive demands resulted in lower performance on one of the secondary tasks, suggesting that more complex listening environments require more effort. Although adults with NH outperformed HA users on speech understanding and auditory localization, the two groups did not differ with respect to secondary task costs.
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http://dx.doi.org/10.1097/AUD.0000000000000963DOI Listing
October 2020

Electrophysiological assessment of temporal envelope processing in cochlear implant users.

Sci Rep 2020 09 21;10(1):15406. Epub 2020 Sep 21.

Department of Neurosciences, KU Leuven, ExpORL, Herestraat 49, Box 721, 3000, Leuven, Belgium.

Cochlear-implant (CI) users rely on temporal envelope modulations (TEMs) to understand speech, and clinical outcomes depend on the accuracy with which these TEMs are encoded by the electrically-stimulated neural ensembles. Non-invasive EEG measures of this encoding could help clinicians identify and disable electrodes that evoke poor neural responses so as to improve CI outcomes. However, recording EEG during CI stimulation reveals huge stimulation artifacts that are up to orders of magnitude larger than the neural response. Here we used a custom-built EEG system having an exceptionally high sample rate to accurately measure the artefact, which we then removed using linear interpolation so as to reveal the neural response during continuous electrical stimulation. In ten adult CI users, we measured the 40-Hz electrically evoked auditory steady-state response (eASSR) and electrically evoked auditory change complex (eACC) to amplitude-modulated 900-pulses-per-second pulse trains, stimulated in monopolar mode (i.e. the clinical default), and at different modulation depths. We successfully measured artifact-free 40-Hz eASSRs and eACCs. Moreover, we found that the 40-Hz eASSR, in contrast to the eACC, showed substantial responses even at shallow modulation depths. We argue that the 40-Hz eASSR is a clinically feasible objective measure to assess TEM encoding in CI users.
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http://dx.doi.org/10.1038/s41598-020-72235-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7506023PMC
September 2020

In-situ sensitivity of a totally-implantable microphone.

Hear Res 2020 09 8;395:108018. Epub 2020 Jul 8.

KU Leuven, University of Leuven, Department of Neurosciences, Research Group ExpORL, Leuven, Belgium; University Hospitals Leuven, Department of Otolaryngology, Head and Neck Surgery, Leuven, Belgium. Electronic address:

One of the key components of fully-implantable hearing devices is the implantable microphone. A crucial parameter when characterizing implantable microphones is the acoustic sensitivity, as it is one of the input parameters for the fitting algorithm and influences the achievable gain. The aim of our study was to investigate the sensitivity of an implanted subcutaneous microphone over time to answer two research questions: (1) How does the sensitivity change once the microphone is implanted under the skin (pre-op versus in-situ)? and (2) How does the sensitivity change from short-term to mid-term? We have measured the in-situ microphone sensitivity in three subjects implanted with a fully-implantable active middle ear implant from 2 weeks up to 20 weeks after implantation with a research software. The microphone sensitivity changed after implantation with clinically relevant changes around the resonance frequency of the microphone. Based on our results, it is essential to measure the in-situ microphone sensitivity at the time of initial fitting of the implant. Once implanted no clinically relevant changes in the microphone sensitivity were observed over time, with a clear decrease in variability over time.
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http://dx.doi.org/10.1016/j.heares.2020.108018DOI Listing
September 2020

Precompensating for spread of excitation in a cochlear implant coding strategy.

Hear Res 2020 09 25;395:107977. Epub 2020 Apr 25.

ExpORL, Dept. Neurosciences, KU Leuven, O&N 2, Herestraat 49, 3000, Leuven, Belgium.

Cochlear implant users' limited ability to understand speech in noisy environments has been linked to the poor spatial resolution and the high degree of spectral smearing associated with the spread of neural excitation. A sound coding algorithm that aims to improve the spectro-temporal representation of the sound signal at the implanted ear by precompensating the electrical stimulation for the spread of excitation is presented in this study. The spread precompensation algorithm was integrated into the standard clinical advanced combination encoder (ACE) strategy and the resulting strategy was called SPACE. SPACE was evaluated acutely with a group of six implant users and was compared to their daily used ACE strategy in terms of preference rating and speech recognition in four-talker babble and stationary speech-shaped noise. While no significant differences in preference rating were observed, speech recognition in four-talker babble was improved by SPACE processing. Analysis of the group results revealed a significant improvement in mean speech reception threshold (SRT) over the ACE strategy of 1.4 dB in four-talker babble, whereas the difference of 0.9 dB in stationary noise did not reach statistical significance. Assessment of individual differences showed that four out of six listeners obtained significant SRT improvements with SPACE and that no subject scored significantly worse compared to ACE. The results suggest that the proposed sound coding strategy has the potential to improve speech perception for cochlear implant users in challenging listening situations.
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http://dx.doi.org/10.1016/j.heares.2020.107977DOI Listing
September 2020

From modulated noise to natural speech: The effect of stimulus parameters on the envelope following response.

Hear Res 2020 08 26;393:107993. Epub 2020 May 26.

ExpORL, Dept. of Neurosciences, KU Leuven, Herestraat 49 Bus 721, 3000, Leuven, Belgium. Electronic address:

Envelope following responses (EFRs) can be evoked by a wide range of auditory stimuli, but for many stimulus parameters the effect on EFR strength is not fully understood. This complicates the comparison of earlier studies and the design of new studies. Furthermore, the most optimal stimulus parameters are unknown. To help resolve this issue, we investigated the effects of four important stimulus parameters and their interactions on the EFR. Responses were measured in 16 normal hearing subjects evoked by stimuli with four levels of stimulus complexity (amplitude modulated noise, artificial vowels, natural vowels and vowel-consonant-vowel combinations), three fundamental frequencies (105 Hz, 185 Hz and 245 Hz), three fundamental frequency contours (upward sweeping, downward sweeping and flat) and three vowel identities (Flemish /a:/, /u:/, and /i:/). We found that EFRs evoked by artificial vowels were on average 4-6 dB SNR larger than responses evoked by the other stimulus complexities, probably because of (unnaturally) strong higher harmonics. Moreover, response amplitude decreased with fundamental frequency but response SNR remained largely unaffected. Thirdly, fundamental frequency variation within the stimulus did not impact EFR strength, but only when rate of change remained low (e.g. not the case for sweeping natural vowels). Finally, the vowel /i:/ appeared to evoke larger response amplitudes compared to /a:/ and /u:/, but analysis power was too small to confirm this statistically. Vowel-dependent differences in response strength have been suggested to stem from destructive interference between response components. We show how a model of the auditory periphery can simulate these interference patterns and predict response strength. Altogether, the results of this study can guide stimulus choice for future EFR research and practical applications.
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http://dx.doi.org/10.1016/j.heares.2020.107993DOI Listing
August 2020

Investigating the Added Value of FreeSurfer's Manual Editing Procedure for the Study of the Reading Network in a Pediatric Population.

Front Hum Neurosci 2020 24;14:143. Epub 2020 Apr 24.

Research Group ExpORL, Department of Neuroscience, KU Leuven, Leuven, Belgium.

Insights into brain anatomy are important for the early detection of neurodevelopmental disorders, such as dyslexia. FreeSurfer is one of the most frequently applied automatized software tools to study brain morphology. However, quality control of the outcomes provided by FreeSurfer is often ignored and could lead to wrong statistical inferences. Additional manual editing of the data may be a solution, although not without a cost in time and resources. Past research in adults on comparing the automatized method of FreeSurfer with and without additional manual editing indicated that although editing may lead to significant differences in morphological measures between the methods in some regions, it does not substantially change the sensitivity to detect clinical differences. Given that automated approaches are more likely to fail in pediatric-and inherently more noisy-data, we investigated in the current study whether FreeSurfer can be applied fully automatically or additional manual edits of T1-images are needed in a pediatric sample. Specifically, cortical thickness and surface area measures with and without additional manual edits were compared in six regions of interest (ROIs) of the reading network in 5-to-6-year-old children with and without dyslexia. Results revealed that additional editing leads to statistical differences in the morphological measures, but that these differences are consistent across subjects and that the sensitivity to reveal statistical differences in the morphological measures between children with and without dyslexia is not affected, even though conclusions of marginally significant findings can differ depending on the method used. Thereby, our results indicate that additional manual editing of reading-related regions in FreeSurfer has limited gain for pediatric samples.
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http://dx.doi.org/10.3389/fnhum.2020.00143DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7194167PMC
April 2020

Subcortical auditory neural synchronization is deficient in pre-reading children who develop dyslexia.

Dev Sci 2020 11 23;23(6):e12945. Epub 2020 Apr 23.

Department of Neurosciences, Research Group Experimental ORL, KU Leuven - University of Leuven, Leuven, Belgium.

Auditory processing of temporal information in speech is sustained by synchronized firing of neurons along the entire auditory pathway. In school-aged children and adults with dyslexia, neural synchronization deficits have been found at cortical levels of the auditory system, however, these deficits do not appear to be present in pre-reading children. An alternative role for subcortical synchronization in reading development and dyslexia has been suggested, but remains debated. By means of a longitudinal study, we assessed cognitive reading-related skills and subcortical auditory steady-state responses (80 Hz ASSRs) in a group of children before formal reading instruction (pre-reading), after 1 year of formal reading instruction (beginning reading), and after 3 years of formal reading instruction (more advanced reading). Children were retrospectively classified into three groups based on family risk and literacy achievement: typically developing children without a family risk for dyslexia, typically developing children with a family risk for dyslexia, and children who developed dyslexia. Our results reveal that children who developed dyslexia demonstrate decreased 80 Hz ASSRs at the pre-reading stage. This effect is no longer present after the onset of reading instruction, due to an atypical developmental increase in 80 Hz ASSRs between the pre-reading and the beginning reading stage. A forward stepwise logistic regression analysis showed that literacy achievement was predictable with an accuracy of 90.4% based on a model including three significant predictors, that is, family risk for dyslexia (R = .31), phonological awareness (R = .23), and 80 Hz ASSRs (R = .26). Given that (1) abnormalities in subcortical ASSRs preceded reading acquisition in children who developed dyslexia and (2) subcortical ASSRs contributed to the prediction of literacy achievement, subcortical auditory synchronization deficits may constitute a pre-reading risk factor in the emergence of dyslexia.
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http://dx.doi.org/10.1111/desc.12945DOI Listing
November 2020

Age Affects Speech Understanding and Multitask Costs.

Ear Hear 2020 Sep/Oct;41(5):1412-1415

Department of Neurosciences, KU Leuven - University of Leuven, Leuven, Belgium.

Objectives: We examined the effect of age on speech understanding and multitask costs in the ecologically relevant "Audiovisual True-to-Life Assessment of Auditory Rehabilitation"-paradigm (AVATAR).

Design: Twenty-nine normal-hearing middle-aged adults completed AVATAR, which combines an auditory-visual speech-in-noise task with three secondary tasks on auditory localization or visual short-term memory in different dual-, triple-, and quadruple-task combinations. Performance decrements on the secondary tasks were considered to reflect the cognitive resources allocated during listening. Self-reported hearing difficulties were administered via a questionnaire. Results were compared with scores of 35 young normal-hearing adults.

Results: Middle-aged adults performed consistently worse than young adults on speech understanding and, in the triple- and quadruple-task combinations only, on secondary task performance. Furthermore, middle-agers reported higher levels of daily listening concentration and more difficulties with speech understanding.

Conclusions: This study demonstrated the adverse effect of age on speech-in-noise understanding and the amount of allocated cognitive resources during challenging listening situations realized in AVATAR.
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http://dx.doi.org/10.1097/AUD.0000000000000848DOI Listing
January 2020

Alteration of the relative vibration of the round window membrane after implantation of a direct acoustic cochlear implant.

Int J Audiol 2020 05 20;59(5):341-347. Epub 2019 Dec 20.

Research Group ExpORL, Department of Neurosciences, KU Leuven, University of Leuven, Leuven, Belgium.

Subjects implanted with a Direct Acoustic Cochlear Implant (DACI) show improvements in their bone conduction (BC) thresholds after surgery. We hypothesised that a new pathway for BC sound is created via the DACI. The aim of this study was to investigate the contribution of this pathway to the cochlear response via measurements of the promontory and round window membrane (RWM) velocities while stimulating with a conventional bone conductor. This study was a cadaver head study with a repeated measures study design. Eight ears of five fresh-frozen cadaveric whole heads were investigated in this trial. After DACI implantation the promontory and RWM velocities did not change significantly in the frequency range 0.5-2 kHz when the DACI was switched off. No significant changes in the relative vibration magnitude of the RWM after DACI implantation were observed. The improvements in BC thresholds seen in patients implanted with a DACI very likely have their origin in the changed impedance at the oval window after DACI surgery leading to a more efficient contribution from the inner ear components to BC sound.
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http://dx.doi.org/10.1080/14992027.2019.1705405DOI Listing
May 2020

Atypical gray matter in children with dyslexia before the onset of reading instruction.

Cortex 2019 12 11;121:399-413. Epub 2019 Oct 11.

Parenting & Special Education Research Unit, Faculty of Psychology & Educational Sciences, KU Leuven, Belgium.

Many studies have focused on neuroanatomical anomalies in dyslexia, yet primarily in school-aged children and adults. In the present study, we investigated gray matter surface area and cortical thickness at the pre-reading stage in a cohort of 54 children, 31 with a family risk for dyslexia and 23 without a family risk for dyslexia, of whom 16 children developed dyslexia. Surface-based analyses in the core regions of the reading network in the left hemisphere and in the corresponding right hemispheric regions were performed in FreeSurfer. Results revealed that pre-readers who develop dyslexia show reduced surface area in bilateral fusiform gyri. In addition, anomalies related to a family risk for dyslexia, irrespectively of later reading ability, were observed in the area of the bilateral inferior and middle temporal gyri. Differences were apparent in surface area, as opposed to cortical thickness. Results indicate that the neuroanatomical anomalies, since they are observed in the pre-reading phase, are not the consequence of impoverished reading experience.
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http://dx.doi.org/10.1016/j.cortex.2019.09.010DOI Listing
December 2019

High-resolution Imaging of the Human Cochlea through the Round Window by means of Optical Coherence Tomography.

Sci Rep 2019 10 3;9(1):14271. Epub 2019 Oct 3.

Research Group Experimental Oto-Rhino-Laryngology, Department of Neurosciences, University of Leuven, Leuven, Belgium.

The human cochlea is deeply embedded in the temporal bone and surrounded by a thick otic capsule, rendering its internal structure inaccessible for direct visualization. Clinical imaging techniques fall short of their resolution for imaging of the intracochlear structures with sufficient detail. As a result, there is a lack of knowledge concerning best practice for intracochlear therapy placement, such as cochlear implantation. In the past decades, optical coherence tomography (OCT) has proven valuable for non-invasive, high-resolution, cross-sectional imaging of tissue microstructure in various fields of medicine, including ophthalmology, cardiology and dermatology. There is an upcoming interest for OCT imaging of the cochlea, which so far was mostly carried out in small animals. In this temporal bone study, we focused on high-resolution imaging of the human cochlea. The cochlea was approached through mastoidectomy and posterior tympanotomy, both standard surgical procedures. A commercially available spectral-domain OCT imaging system was used to obtain high-resolution images of the cochlear hook region through the intact round window membrane in four cadaveric human temporal bones. We discuss the qualitative and quantitative characteristics of intracochlear structures on OCT images and their importance for cochlear implant surgery.
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http://dx.doi.org/10.1038/s41598-019-50727-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6776619PMC
October 2019

Neural Modulation Transmission Is a Marker for Speech Perception in Noise in Cochlear Implant Users.

Ear Hear 2020 May/Jun;41(3):591-602

KU Leuven, Department of Neurosciences, ExpORL, Leuven, Belgium.

Objectives: Cochlear implants (CIs) restore functional hearing in persons with a severe hearing impairment. Despite being one of the most successful bionic prosthesis, performance with CI (in particular speech understanding in noise) varies considerably across its users. The ability of the auditory pathway to encode temporal envelope modulations (TEMs) and the effect of degenerative processes associated with hearing loss on TEM encoding is assumed to be one of the reasons underlying the large intersubject differences in CI performance. The objective of the present study was to investigate how TEM encoding of the stimulated neural ensembles of human CI recipients is related to speech perception in noise (SPIN).

Design: We used electroencephalography as a noninvasive electrophysiological measure to assess TEM encoding in the auditory pathway of CI users by means of the 40-Hz electrically evoked auditory steady state response (EASSR). Nine CI users with a wide range of SPIN outcome were included in the present study. TEM encoding was assessed for each stimulation electrode of each subject and new metrics; the CI neural modulation transmission difference (CIMTD) and the CI neural modulation transmission index (CIMTI) were developed to quantify the amount of variability in TEM encoding across the stimulated neural ensembles of the CI electrode array.

Results: EASSR patterns varied across the CI electrode array and subjects. We found a strong correlation (r = 0.89, p = 0.001) between the SPIN outcomes and the variability in EASSR amplitudes across the array as assessed with CIMTD/CIMTI.

Conclusions: The results of the present study show that the 40-Hz EASSR can be used to objectively assess the neural encoding of TEMs in human CI recipients. Overall reduced or largely variable TEM encoding of the neural ensembles across the electrode array, as quantified with the CIMTD/CIMTI, is highly correlated with speech perception in noise outcome with a CI.
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http://dx.doi.org/10.1097/AUD.0000000000000783DOI Listing
October 2019

AVATAR Assesses Speech Understanding and Multitask Costs in Ecologically Relevant Listening Situations.

Ear Hear 2020 May/Jun;41(3):521-531

KU Leuven, Department of Neurosciences, ExpORL, B-3000 Leuven, Belgium.

Objectives: There is a high need among clinicians and researchers for an ecologically valid measure of auditory functioning and listening effort. Therefore, we developed AVATAR: an "Audiovisual True-to-life Assessment of Auditory Rehabilitation" which takes important characteristics of real-life listening situations into account, such as multimodal speech presentation, spatial separation of sound sources and multitasking. As such, AVATAR aims to assess both auditory functioning and the amount of allocated processing resources during listening in a realistic yet controllable way. In the present study, we evaluated AVATAR and investigated whether speech understanding in noise and multitask costs during realistic listening environments changed with increasing task complexity.

Design: Thirty-five young normal-hearing participants performed different task combinations of an auditory-visual speech-in-noise task and three secondary tasks on both auditory localization and visual short-term memory in a simulated restaurant environment. Tasks were combined in increasing complexity and multitask costs on the secondary tasks were investigated as an estimate of the amount of cognitive resources allocated during listening and multitasking. In addition to behavioral measures of auditory functioning and effort, working memory capacity and self-reported hearing difficulties were established using a reading span test and a questionnaire on daily hearing abilities.

Results: Whereas performance on the speech-in-noise task was not affected by task complexity, multitask costs on one of the secondary tasks became significantly larger with increasing task complexity. Working memory capacity correlated significantly with multitask costs, but no association was observed between behavioral outcome measures and self-reported hearing abilities or effort.

Conclusions: AVATAR proved to be a promising model to assess speech intelligibility and auditory localization abilities and to gauge the amount of processing resources during effortful listening in ecologically relevant multitasking situations by means of multitask costs. In contrast with current clinical measures of auditory functioning, results showed that listening and multitasking in challenging listening environments can require a considerable amount of processing resources, even for young normal-hearing adults. Furthermore, the allocation of resources increased in more demanding listening situations. These findings open avenues for a more realistic assessment of auditory functioning and individually tuned auditory rehabilitation for individuals of different age and hearing profiles.
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http://dx.doi.org/10.1097/AUD.0000000000000778DOI Listing
July 2019

Improving the efficiency of the digit triplet test using digit scoring with variable adaptive step sizes.

Int J Audiol 2019 10 12;58(10):670-677. Epub 2019 Jun 12.

KU Leuven, Department of Neurosciences, ExpORL , Leuven , Belgium.

To investigate modifications of the Flemish Digit Triplet Test (DTT) to improve its efficiency, i.e. the use of a low-pass filtered noise and variable adaptive step sizes according to a digit scoring procedure, targeting different recognition probabilities. Speech reception thresholds (SRT) were evaluated in terms of their test-retest reliability and correlation with pure tone averages (PTA) in a group of 68 adult participants with different degrees of hearing impairment. The use of a low-pass filtered noise did not result in better test-retest reliability or an improved SRT-PTA correlation. Using digit scoring with adaptive step sizes parametrised to target a recognition probability of 79% (D79), corresponding to the recognition probability of the currently used DTT with triplet scoring and fixed adaptive step sizes of 2 dB, increased test-retest reliability. Lower recognition probabilities of 57 and 35% demonstrated worse reliability and worse SRT-PTA correlations. Given the increased test-retest reliability of D79, a similar reliability as for the currently used DTT could be obtained after considerably fewer trials, leading to a profit in test duration.
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http://dx.doi.org/10.1080/14992027.2019.1622042DOI Listing
October 2019

The effect of stimulus envelope shape on the auditory steady-state response.

Hear Res 2019 09 28;380:22-34. Epub 2019 May 28.

ExpORL, Dept. of Neurosciences, KU Leuven, Herestraat 49 Bus 721, 3000, Leuven, Belgium. Electronic address:

Auditory steady-state responses (ASSRs) are auditory evoked potentials that reflect phase-locked neural activity to periodic stimuli. ASSRs are often evoked by tones with a modulated envelope, with sinusoidal envelopes being most common. However, it is unclear if and how the shape of the envelope affects ASSR responses. In this study, we used various trapezoidal modulated tones to evoke ASSRs (modulation frequency = 40 Hz) and studied the effect of four envelope parameters: attack time, hold time, decay time and off time. ASSR measurements in 20 normal hearing subjects showed that envelope shape significantly influenced responses: increased off time and/or increased decay time led to responses with a larger signal-to-noise-ratio (SNR). Response phase delay was significantly influenced by attack time and to a lesser degree by off time. We also simulated neural population responses that approximate ASSRs with a model of the auditory periphery (Bruce et al. 2018). The modulation depth of the simulated responses, i.e. the difference between maximum and minimum firing rate, correlated highly with the response SNRs found in the ASSR measurements. Longer decay time and off time enhanced the modulation depth both by decreasing the minimum firing rate and by increasing the maximum firing rate. In conclusion, custom envelopes with long decay and off time provide larger response SNRs and the benefit over the commonly used sinusoidal envelope was in the range of several dB.
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http://dx.doi.org/10.1016/j.heares.2019.05.007DOI Listing
September 2019

Brain activity patterns of phonemic representations are atypical in beginning readers with family risk for dyslexia.

Dev Sci 2020 01 21;23(1):e12857. Epub 2019 Jun 21.

Department of Cognitive Neuroscience and Maastricht Brain Imaging Center, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.

There is an ongoing debate whether phonological deficits in dyslexics should be attributed to (a) less specified representations of speech sounds, like suggested by studies in young children with a familial risk for dyslexia, or (b) to an impaired access to these phonemic representations, as suggested by studies in adults with dyslexia. These conflicting findings are rooted in between study differences in sample characteristics and/or testing techniques. The current study uses the same multivariate functional MRI (fMRI) approach as previously used in adults with dyslexia to investigate phonemic representations in 30 beginning readers with a familial risk and 24 beginning readers without a familial risk of dyslexia, of whom 20 were later retrospectively classified as dyslexic. Based on fMRI response patterns evoked by listening to different utterances of /bA/ and /dA/ sounds, multivoxel analyses indicate that the underlying activation patterns of the two phonemes were distinct in children with a low family risk but not in children with high family risk. However, no group differences were observed between children that were later classified as typical versus dyslexic readers, regardless of their family risk status, indicating that poor phonemic representations constitute a risk for dyslexia but are not sufficient to result in reading problems. We hypothesize that poor phonemic representations are trait (family risk) and not state (dyslexia) dependent, and that representational deficits only lead to reading difficulties when they are present in conjunction with other neuroanatomical or-functional deficits.
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http://dx.doi.org/10.1111/desc.12857DOI Listing
January 2020