Auditory steady-state responses (ASSRs) in EEG measurements are currently used for reliable heari... more Auditory steady-state responses (ASSRs) in EEG measurements are currently used for reliable hearing threshold estimation at audiometric frequencies. Especially newborns with hearing problems benefit from this technique, as with this information diagnosis can be better specified and hearing aids can be better fitted at an early age. Unfortunately measurement duration is still very long for clinical widespread use due to the lack of efficient signal detection techniques with sufficient robustness against artifacts. In this paper, a simplified procedural framework for ASSR detection is worked out that allows the development of a multichannel processing strategy, starting from a detection theory approach. It is shown that a sufficient statistic can be calculated that best captures the amount of ASSR in the recorded data. The evaluation is conducted using data from ten normal-hearing adults. It is concluded that most single-and multichannel approaches are similar in performance when applied to uncontaminated EEG. When artifact-rich EEG is used, the proposed detection theory based approach significantly improves the number of ASSR detections compared with a noise-weighted common EEG channel derivation (vertex-occiput).
The reliability of algorithms for room acoustic simulations has often been confirmed on the basis... more The reliability of algorithms for room acoustic simulations has often been confirmed on the basis of the verification of predicted room acoustical parameters. This paper presents a complementary perceptual validation procedure consisting of two experiments, respectively dealing with speech intelligibility, and with sound source front–back localisation.The evaluated simulation algorithm, implemented in software ODEON®, is a hybrid method that is based on an image source algorithm for the prediction of early sound reflection and on ray-tracing for the later part, using a stochastic scattering process with secondary sources. The binaural room impulse response (BRIR) is calculated from a simulated room impulse response where information about the arriving time, intensity and spatial direction of each sound reflection is collected and convolved with a measured Head Related Transfer Function (HRTF). The listening stimuli for the speech intelligibility and localisation tests are auralised convolutions of anechoic sound samples with measured and simulated BRIRs.Perception tests were performed with human subjects in two acoustical environments, i.e. an anechoic and reverberant room, by presenting the stimuli to subjects in a natural way, and via headphones by using two non-individualized HRTFs (artificial head and hearing aids placed on the ears of the artificial head) of both a simulated and a real room.Very good correspondence is found between the results obtained with simulated and measured BRIRs, both for speech intelligibility in the presence of noise and for sound source localisation tests. In the anechoic room an increase in speech intelligibility is observed when noise and signal are presented from sources located at different angles. This improvement is not so evident in the reverberant room, with the sound sources at 1-m distance from the listener. Interestingly, the performance of people for front–back localisation is better in the reverberant room than in the anechoic room.The correlation between people’s ability for sound source localisation on one hand, and their ability for recognition of binaurally received speech in reverberation on the other hand, is found to be weak.
Journal of The Acoustical Society of America, 2008
Geometrical-acoustics ͑GA͒ modeling techniques assume that surfaces are large relative to the wav... more Geometrical-acoustics ͑GA͒ modeling techniques assume that surfaces are large relative to the wavelengths of interest. For a given scenario, practitioners typically create a single 3D model with large, flat surfaces that satisfy the assumption over a broad range of frequencies. Such geometric approximations lead to errors in the spatial distribution of the simulated sound field because geometric details that influence reflection and scattering behavior are omitted. To compensate for the approximations, modelers typically estimate scattering coefficients for the surfaces to account stochastically for the actual, wavelength-dependent variations in reflection directionality. A more deterministic approach could consider a series of models with increasing geometric detail, each to be analyzed at a corresponding frequency band for which the requirement of large surface dimensions is satisfied. Thus, to improve broadband spatial accuracy for GA simulations, we propose a multiresolution modeling approach. Using scale model measurements of a corrugated wall, comparisons of our method with non-GA techniques, and some simple listening tests, we will demonstrate that multiresolution geometry provides more spatially accurate results than single-resolution approximations when using GA techniques, and that this improved accuracy is aurally significant. 8:20 5aAAa2. On the analysis of the time spreading of sound diffusers. Acoustics'08 Paris ͑slit and "wide obstacle" with two edges͒. The results have again been compared with Svensson's exact wave-theoretical secondary edge source model. With some restrictions, they seem to indicate, that indeed even diffraction of sound -like light -may be handled as flow of particles. To avoid the feared explosion of computation time with higher order diffraction, a beam reunification may now be achieved by Quantized Pyramidal Beam Tracing.
This study investigates the usage of virtual acoustics in the framework of a research project dea... more This study investigates the usage of virtual acoustics in the framework of a research project dealing with the development of the binaural hearing aids and cochlear implants, with emphasis on the localisation of sound in different acoustical scenarios. Virtual acoustics allows the convolution of a measured head related transfer function (HRTF's) with the impulse response of a room generated by a computer model (using ODEON® software) to realistically simulate binaural sound. We report on (loud)speaker localization experiments conducted in a reverberant room, where eight listening subjects were asked to localize sound sources in the front horizontal plane. In the experiment, three different stimuli were used: high frequency sound around 3150 Hz, middle frequency sound in the 500 Hz band and the sound of a ringing telephone. The stimuli were played individually (1) from thirteen real loudspeakers, (2) as virtually 3D sounds via headphones, based on in situ binaural room impulse responses recorded by an artificial head, and (3) via headphones, as virtual sources simulated in ODEON® software (using HRTF receiver properties as measured on the artificial head). The results from the reverberant room are compared with listening tests performed in anechoic conditions with the same listening subjects.
On the basis of a statistical evaluation of the binaural sound source localization performance du... more On the basis of a statistical evaluation of the binaural sound source localization performance during listening tests by human subjects, we show that the convolution of a measured head-related transfer function (HRTF) with the room impulse response generated by a hybrid image source model with a stochastic scattering process using secondary sources
Proceedings of the National Academy of Sciences, 2010
Developmental dyslexia is characterized by severe reading and spelling difficulties that are pers... more Developmental dyslexia is characterized by severe reading and spelling difficulties that are persistent and resistant to the usual didactic measures and remedial efforts. It is well established that a major cause of these problems lies in poorly specified representations of speech sounds. One hypothesis states that this phonological deficit results from a more fundamental deficit in auditory processing. Despite substantial research effort, the specific nature of these auditory problems remains debated. A first controversy concerns the speech specificity of the auditory processing problems: Can they be reduced to more basic auditory processing, or are they specific to the perception of speech sounds? A second topic of debate concerns the extent to which the auditory problems are specific to the processing of rapidly changing temporal information or whether they encompass a broader range of complex spectrotemporal processing. By applying a balanced design with stimuli that were adequately controlled for acoustic complexity, we show that adults with dyslexia are specifically impaired at categorizing speech and nonspeech sounds that differ in terms of rapidly changing acoustic cues (i.e., temporal cues), but that they perform adequately when categorizing steady-state speech and nonspeech sounds. Thus, we show that individuals with dyslexia have an auditory temporal processing deficit that is not speech-specific. auditory processing | categorical perception | speech perception S peech contains a number of acoustic cues that are used to discriminate speech sounds belonging to different phonetic categories. For example, the acoustic cue that is critical for differentiating /bA/ versus /dA/, a stop consonant followed by a vowel, lies within the first 100 ms of the sounds, during which time the frequency of the second formant changes rapidly (i.e., a temporal cue). In contrast, the acoustic difference between two vowels such as /u/ versus /y/ lies in the frequency of the second formant, which stays relatively stable over time. Hence, an accurate perception of steady-state (i.e., nontemporal) spectral cues is essential for identification of these vowels. There is ample evidence that individuals with dyslexia exhibit problems in the representation of speech sounds (1), and that these may be rooted in a more fundamental auditory processing deficit (2). Originally, it was claimed that individuals with dyslexia have ad e ficit in processing auditory cues that are "temporal" in nature (i.e., rapidly changing), thereby causing problems in the accurate processing of rapid acoustic changes in speech (such as in stop consonants) (3). This speech perception problem was thought to consequently cause a cascade of effects, starting with the disruption of the normal development of the phonological system, eventually resulting in problems learning to read and spell. However, despite substantial research efforts, the literature is not concordant with respect to the specific nature of these auditory problems. In particular, it is unclear (i) whether the problem is specific to the perception of speech sounds (4) or whether it includes basic acoustic processing more generally , and (ii) whether the auditory problem is specific to rapid temporal processing (3, 5) or whether it encompasses a broader range of spectro-temporal processing abilities (6).
The etiology of developmental dyslexia remains widely debated. An appealing theory postulates tha... more The etiology of developmental dyslexia remains widely debated. An appealing theory postulates that the reading and spelling problems in individuals with dyslexia originate from reduced sensitivity to slow-rate dynamic auditory cues. This low-level auditory deficit is thought to provoke a cascade of effects, including inaccurate speech perception and eventually unspecified phoneme representations. The present study investigated sensitivity to frequency modulation and amplitude rise time, speech-in-noise perception and phonological awareness in 11-year-old children with dyslexia and a matched normal-reading control children. Group comparisons demonstrated that children with dyslexia were less sensitive than normal-reading children to slow-rate dynamic auditory processing, speech-in-noise perception, phonological awareness and literacy abilities. Correlations were found between slow-rate dynamic auditory processing and phonological awareness, and speech-in-noise perception and reading. Yet, no significant correlation between slow-rate dynamic auditory processing and speech-in-noise perception was obtained. Together, these results indicate that children with dyslexia have difficulties with slow-rate dynamic auditory processing and speech-in-noise perception and that these problems persist until sixth grade.
Amplitude modulations in the speech envelope are crucial elements for speech perception. These mo... more Amplitude modulations in the speech envelope are crucial elements for speech perception. These modulations comprise the processing rate at which syllabic (∼3-7 Hz), and phonemic transitions occur in speech. Theories about speech perception hypothesize that each hemisphere in the auditory cortex is specialized in analyzing modulations at different timescales, and that phonemic-rate modulations of the speech envelope lateralize to the left hemisphere, whereas right lateralization occurs for slow, syllabic-rate modulations. In the present study, neural processing of phonemic- and syllabic-rate modulations was investigated with auditory steady-state responses (ASSRs). ASSRs to speech-weighted noise stimuli, amplitude modulated at 4, 20, and 80 Hz, were recorded in 30 normal-hearing adults. The 80 Hz ASSR is primarily generated by the brainstem, whereas 20 and 4 Hz ASSRs are mainly cortically evoked and relate to speech perception. Stimuli were presented diotically (same signal to both ears) and monaurally (one signal to the left or right ear). For 80 Hz, diotic ASSRs were larger than monaural responses. This binaural advantage decreased with decreasing modulation frequency. For 20 Hz, diotic ASSRs were equal to monaural responses, while for 4 Hz, diotic responses were smaller than monaural responses. Comparison of left and right ear stimulation demonstrated that, with decreasing modulation rate, a gradual change from ipsilateral to right lateralization occurred. Together, these results (1) suggest that ASSR enhancement to binaural stimulation decreases in the ascending auditory system and (2) indicate that right lateralization is more prominent for low-frequency ASSRs. These findings may have important consequences for electrode placement in clinical settings, as well as for the understanding of low-frequency ASSR generation.
"Objectives: Speech intelligibility is strongly influenced by the ability to process temporal mod... more "Objectives: Speech intelligibility is strongly influenced by the ability to process temporal modulations. It is hypothesized that in dyslexia, deficient processing of rapidly-changing auditory information underlies a deficient development of phonological representations, causing reading and spelling problems. Low-frequency modulations between 4 and 20 Hz correspond to the processing rate of important phonological segments (syllables and phonemes respectively) in speech and therefore provide a bridge between low-level auditory and phonological processing. In the present study, temporal modulation processing was investigated by auditory steady state responses (ASSRs) in normal-reading and dyslexic adults.
Design: Multichannel ASSRs were recorded in normal-reading and dyslexic adults in response to speech-weighted noise stimuli amplitude modulated at 80 Hz, 20 Hz and 4 Hz. The 80 Hz modulation is known to be primarily generated by the brainstem, whereas the 20 Hz and 4 Hz modulations are mainly generated in the cortex. Furthermore, the 20 Hz and 4 Hz modulations provide an objective auditory performance measure related to phonemic-rate and syllabic-rate processing. In addition to neurophysiological measures, psychophysical tests of speech-in-noise perception and phonological awareness were assessed.
Results: Based on response-strength and phase coherence measures, normal-reading and dyslexic participants showed similar processing at the brainstem level. At the cortical level of the auditory system, dyslexic subjects demonstrated deviant phonemic-rate responses compared to normal readers, whereas no group differences were found for the syllabic-rate. Furthermore, a relation between phonemic-rate ASSRs and psychophysical tests of speech-in-noise perception and phonological awareness was obtained.
Conclusions: These results suggest reduced cortical processing for phonemic-rate modulations in dyslexic adults, presumably resulting in limited integration of temporal information in the dorsal phonological pathway."
The etiology of developmental dyslexia remains widely debated. An appealing theory postulates tha... more The etiology of developmental dyslexia remains widely debated. An appealing theory postulates that the reading and spelling problems in individuals with dyslexia originate from reduced sensitivity to slow-rate dynamic auditory cues. This low-level auditory deficit is thought to provoke a cascade of effects, including inaccurate speech perception and eventually unspecified phoneme representations. The present study investigated sensitivity to frequency modulation and amplitude rise time, speech-in-noise perception and phonological awareness in 11-year-old children with dyslexia and a matched normal-reading control children. Group comparisons demonstrated that children with dyslexia were less sensitive than normal-reading children to slow-rate dynamic auditory processing, speech-in-noise perception, phonological awareness and literacy abilities. Correlations were found between slow-rate dynamic auditory processing and phonological awareness, and speech-in-noise perception and reading. Yet, no significant correlation between slow-rate dynamic auditory processing and speech-in-noise perception was obtained. Together, these results indicate that children with dyslexia have difficulties with slow-rate dynamic auditory processing and speech-in-noise perception and that these problems persist until sixth grade.
Developmental dyslexia is characterized by severe reading and spelling difficulties that are pers... more Developmental dyslexia is characterized by severe reading and spelling difficulties that are persistent and resistant to the usual didactic measures and remedial efforts. It is well established that a major cause of these problems lies in poorly specified representations of speech sounds. One hypothesis states that this phonological deficit results from a more fundamental deficit in auditory processing. Despite substantial research effort, the specific nature of these auditory problems remains debated. A first controversy concerns the speech specificity of the auditory processing problems: Can they be reduced to more basic auditory processing, or are they specific to the perception of speech sounds?A second topic of debate concerns the extent to which the auditory problems are specific to the processing of rapidly changing temporal information or whether they encompass a broader range of complex spectrotemporal processing. By applying a balanced design with stimuli that were adequately controlled for acoustic complexity, we show that adults with dyslexia are specifically impaired at categorizing speech and nonspeech sounds that differ in terms of rapidly changing acoustic cues (i.e., temporal cues), but that they perform adequately when categorizing steady-state speech and nonspeech sounds. Thus, we show that individuals with dyslexia have an auditory temporal processing deficit that is not speech-specific.
Developmental dyslexia is characterized by severe reading and spelling difficulties that are pers... more Developmental dyslexia is characterized by severe reading and spelling difficulties that are persistent and resistant to the usual didactic measures and remedial efforts. It is well established that a major cause of these problems lies in poorly specified phonological representations. Many individuals with dyslexia also present impairments in auditory temporal processing and speech perception, but it remains debated whether these more basic perceptual impairments play a role in causing the reading problem. Longitudinal studies may help clarifying this issue by assessing preschool children before they receive reading instruction and by following them up through literacy development. The current longitudinal study shows impairments in auditory frequency modulation (FM) detection, speech perception and phonological awareness in kindergarten and in grade 1 in children who receive a dyslexia diagnosis in grade 3. FM sensitivity and speech-in-noise perception in kindergarten uniquely contribute to growth in reading ability, even after controlling for letter knowledge and phonological awareness. These findings indicate that impairments in auditory processing and speech perception are not merely an epiphenomenon of reading failure. Although no specific directional relations were observed between auditory processing, speech perception and phonological awareness, the highly significant concurrent and predictive correlations between all these variables suggest a reciprocal association and corroborate the evidence for the auditory deficit theory of dyslexia.
Diffusion tensor imaging tractography is a structural magnetic resonance imaging technique allowi... more Diffusion tensor imaging tractography is a structural magnetic resonance imaging technique allowing reconstruction and assessment of the integrity of three dimensional white matter tracts, as indexed by their fractional anisotropy. It is assumed that the left arcuate fasciculus plays a crucial role for reading development, as it connects two regions of the reading network, the left temporoparietal region and the left inferior frontal gyrus, for which atypical functional activation and lower fractional anisotropy values have been reported in dyslexic readers. In addition, we explored the potential role of the left inferior fronto-occipital fasciculus, which might connect a third region of the reading network, the left ventral occipitotemporal region with the left inferior frontal gyrus. In the present study, 20 adults with dyslexia and 20 typical reading adults were scanned using diffusion tensor imaging, and the bilateral arcuate fasciculus and the left inferior fronto-occipital fasciculus were delineated. Group comparisons show a significantly reduced fractional anisotropy in the left arcuate fasciculus of adults with dyslexia, in particular in the segment that directly connects posterior temporal and frontal areas. This fractional anisotropy reduction might reflect a lower degree of myelination in the dyslexic sample, as it co-occurred with a group difference in radial diffusivity. In contrast, no significant group differences in fractional anisotropy were found in the right arcuate fasciculus or in the left inferior fronto-occipital fasciculus. Correlational analyses (controlled for reading status) demonstrated a specific relation between performance on phoneme awareness and speech perception and the integrity of left arcuate fasciculus as indexed by fractional anisotropy, and between orthographic processing and fractional anisotropy values in left inferior fronto-occipital fasciculus. The present study reveals structural anomalies in the left arcuate fasciculus in adults with dyslexia. This finding corroborates current hypotheses of dyslexia as a disorder of network connections. In addition, our study demonstrates a correlational double dissociation, which might reflect neuroanatomical correlates of the dual route reading model: the left arcuate fasciculus seems to sustain the dorsal phonological route underlying grapheme-phoneme decoding, while the left inferior fronto-occipital fasciculus seems to sustain the ventral orthographic route underlying reading by direct word access.
Objective: Neonatal hearing screening programs in Flanders and the Netherlands use Natus ALGO scr... more Objective: Neonatal hearing screening programs in Flanders and the Netherlands use Natus ALGO screening devices. Since 2006 in Flanders and 2009 in the Netherlands, both programs have replaced the older ALGO Portable devices with the newer ALGO 3i devices. However, in both countries, ALGO 3i devices have a significantly higher rate of referrals than ALGO Portable devices. In Flanders, the refer rate has more than doubled with the switch to ALGO 3i devices. In the Netherlands, screening centers which used ALGO 3i devices also showed a significant increase in referrals. In both countries, the percentage of children diagnosed with permanent hearing loss remained approximately the same. Design: A technical comparison of both device types was carried out to identify possible causes for the increase in referrals. The stimulus output of two ALGO Portable and three ALGO 3i devices was recorded and analysed for stimulus level, spectral properties, and stimulus irregularities. Results: ALGO 3i devices stimulate at a peak level 4.6 dB lower than ALGO Portable devices, have a different stimulus spectrum and show unexplained stimulus irregularities during 4% of the stimulation time. Conclusions: A number of technical differences were found between both device types which could explain the increase in referrals.
The use of binaural pitch stimuli to test for the presence of binaural auditory impairment in rea... more The use of binaural pitch stimuli to test for the presence of binaural auditory impairment in reading-disabled subjects has so far led to contradictory outcomes. While some studies found that a majority of dyslexic subjects was unable to perceive binaural pitch, others obtained a clear response of dyslexic listeners to Huggins' pitch (HP). The present study clarified whether impaired binaural pitch perception is found in dyslexia. Results from a pitch contour identification test, performed in 31 dyslexic listeners and 31 matched controls, clearly showed that dyslexics perceived HP as well as the controls. Both groups also showed comparable results with a similar-sounding, but monaurally detectable, pitch-evoking stimulus. However, nine of the dyslexic subjects were found to have difficulty identifying pitch contours both in the binaural and the monaural conditions. The ability of subjects to correctly identify pitch contours was found to be significantly correlated to measures of frequency discrimination. This correlation may be attributed to the similarity of the experimental tasks and probably reflects impaired cognitive mechanisms related to auditory memory or auditory attention rather than impaired low-level auditory processing per se.
Diffusion tensor imaging tractography is a structural magnetic resonance imaging technique allowi... more Diffusion tensor imaging tractography is a structural magnetic resonance imaging technique allowing reconstruction and assessment of the integrity of three dimensional white matter tracts, as indexed by their fractional anisotropy. It is assumed that the left arcuate fasciculus plays a crucial role for reading development, as it connects two regions of the reading network, the left temporoparietal region and the left inferior frontal gyrus, for which atypical functional activation and lower fractional anisotropy values have been reported in dyslexic readers. In addition, we explored the potential role of the left inferior fronto-occipital fasciculus, which might connect a third region of the reading network, the left ventral occipitotemporal region with the left inferior frontal gyrus. In the present study, 20 adults with dyslexia and 20 typical reading adults were scanned using diffusion tensor imaging, and the bilateral arcuate fasciculus and the left inferior fronto-occipital fasciculus were delineated. Group comparisons show a significantly reduced fractional anisotropy in the left arcuate fasciculus of adults with dyslexia, in particular in the segment that directly connects posterior temporal and frontal areas. This fractional anisotropy reduction might reflect a lower degree of myelination in the dyslexic sample, as it co-occurred with a group difference in radial diffusivity. In contrast, no significant group differences in fractional anisotropy were found in the right arcuate fasciculus or in the left inferior fronto-occipital fasciculus. Correlational analyses (controlled for reading status) demonstrated a specific relation between performance on phoneme awareness and speech perception and the integrity of left arcuate fasciculus as indexed by fractional anisotropy, and between orthographic processing and fractional anisotropy values in left inferior fronto-occipital fasciculus. The present study reveals structural anomalies in the left arcuate fasciculus in adults with dyslexia. This finding corroborates current hypotheses of dyslexia as a disorder of network connections. In addition, our study demonstrates a correlational double dissociation, which might reflect neuroanatomical correlates of the dual route reading model: the left arcuate fasciculus seems to sustain the dorsal phonological route underlying grapheme-phoneme decoding, while the left inferior fronto-occipital fasciculus seems to sustain the ventral orthographic route underlying reading by direct word access.
Auditory processing problems in persons with dyslexia are still subject to debate, and one centra... more Auditory processing problems in persons with dyslexia are still subject to debate, and one central issue concerns the specific nature of the deficit. In particular, it is questioned whether the deficit is specific to speech and/or specific to temporal processing. To resolve this issue, a categorical perception identification task was administered in thirteen 11-year old dyslexic readers and 25 matched normal readers using 4 sound continua: (1) a speech contrast exploiting temporal cues (/bA/-/dA/), (2) a speech contrast defined by nontemporal spectral cues (/u/-/y/), (3) a nonspeech temporal contrast (spectrally rotated/ bA/-/da/), and (4) a nonspeech nontemporal contrast (spectrally rotated/u/-/y/). Results indicate that children with dyslexia are less consistent in classifying speech and nonspeech sounds on the basis of rapidly changing (i.e., temporal) information whereas they are unimpaired in steady-state speech and nonspeech sounds. The deficit is thus restricted to categorizing sounds on the basis of temporal cues and is independent of the speech status of the stimuli. The finding of a temporal-specific but not speech-specific deficit in children with dyslexia is in line with findings obtained in adults using the same paradigm (Vandermosten et al., 2010, Proceedings of the National Academy of Sciences of the United States of America, 107: 10389–10394). Comparison of the child and adult data indicates that the consistency of categorization considerably improves between late childhood and adulthood, particularly for the continua with temporal cues. Dyslexic and normal readers show a similar developmental progress with the dyslexic readers lagging behind both in late childhood and in adulthood.
Objectives: Speech intelligibility is strongly influenced by the ability to process temporal modu... more Objectives: Speech intelligibility is strongly influenced by the ability to process temporal modulations. It is hypothesized that in dyslexia, deficient processing of rapidly changing auditory information underlies a deficient development of phonological representations, causing reading and spelling problems. Low-frequency modulations between 4 and 20 Hz correspond to the processing rate of important phonological segments (syllables and phonemes, respectively) in speech and therefore provide a bridge between low-level auditory and phonological processing. In the present study, temporal modulation processing was investigated by auditory steady state responses (ASSRs) in normalreading and dyslexic adults.
Auditory steady-state responses (ASSRs) in EEG measurements are currently used for reliable heari... more Auditory steady-state responses (ASSRs) in EEG measurements are currently used for reliable hearing threshold estimation at audiometric frequencies. Especially newborns with hearing problems benefit from this technique, as with this information diagnosis can be better specified and hearing aids can be better fitted at an early age. Unfortunately measurement duration is still very long for clinical widespread use due to the lack of efficient signal detection techniques with sufficient robustness against artifacts. In this paper, a simplified procedural framework for ASSR detection is worked out that allows the development of a multichannel processing strategy, starting from a detection theory approach. It is shown that a sufficient statistic can be calculated that best captures the amount of ASSR in the recorded data. The evaluation is conducted using data from ten normal-hearing adults. It is concluded that most single-and multichannel approaches are similar in performance when applied to uncontaminated EEG. When artifact-rich EEG is used, the proposed detection theory based approach significantly improves the number of ASSR detections compared with a noise-weighted common EEG channel derivation (vertex-occiput).
The reliability of algorithms for room acoustic simulations has often been confirmed on the basis... more The reliability of algorithms for room acoustic simulations has often been confirmed on the basis of the verification of predicted room acoustical parameters. This paper presents a complementary perceptual validation procedure consisting of two experiments, respectively dealing with speech intelligibility, and with sound source front–back localisation.The evaluated simulation algorithm, implemented in software ODEON®, is a hybrid method that is based on an image source algorithm for the prediction of early sound reflection and on ray-tracing for the later part, using a stochastic scattering process with secondary sources. The binaural room impulse response (BRIR) is calculated from a simulated room impulse response where information about the arriving time, intensity and spatial direction of each sound reflection is collected and convolved with a measured Head Related Transfer Function (HRTF). The listening stimuli for the speech intelligibility and localisation tests are auralised convolutions of anechoic sound samples with measured and simulated BRIRs.Perception tests were performed with human subjects in two acoustical environments, i.e. an anechoic and reverberant room, by presenting the stimuli to subjects in a natural way, and via headphones by using two non-individualized HRTFs (artificial head and hearing aids placed on the ears of the artificial head) of both a simulated and a real room.Very good correspondence is found between the results obtained with simulated and measured BRIRs, both for speech intelligibility in the presence of noise and for sound source localisation tests. In the anechoic room an increase in speech intelligibility is observed when noise and signal are presented from sources located at different angles. This improvement is not so evident in the reverberant room, with the sound sources at 1-m distance from the listener. Interestingly, the performance of people for front–back localisation is better in the reverberant room than in the anechoic room.The correlation between people’s ability for sound source localisation on one hand, and their ability for recognition of binaurally received speech in reverberation on the other hand, is found to be weak.
Journal of The Acoustical Society of America, 2008
Geometrical-acoustics ͑GA͒ modeling techniques assume that surfaces are large relative to the wav... more Geometrical-acoustics ͑GA͒ modeling techniques assume that surfaces are large relative to the wavelengths of interest. For a given scenario, practitioners typically create a single 3D model with large, flat surfaces that satisfy the assumption over a broad range of frequencies. Such geometric approximations lead to errors in the spatial distribution of the simulated sound field because geometric details that influence reflection and scattering behavior are omitted. To compensate for the approximations, modelers typically estimate scattering coefficients for the surfaces to account stochastically for the actual, wavelength-dependent variations in reflection directionality. A more deterministic approach could consider a series of models with increasing geometric detail, each to be analyzed at a corresponding frequency band for which the requirement of large surface dimensions is satisfied. Thus, to improve broadband spatial accuracy for GA simulations, we propose a multiresolution modeling approach. Using scale model measurements of a corrugated wall, comparisons of our method with non-GA techniques, and some simple listening tests, we will demonstrate that multiresolution geometry provides more spatially accurate results than single-resolution approximations when using GA techniques, and that this improved accuracy is aurally significant. 8:20 5aAAa2. On the analysis of the time spreading of sound diffusers. Acoustics'08 Paris ͑slit and "wide obstacle" with two edges͒. The results have again been compared with Svensson's exact wave-theoretical secondary edge source model. With some restrictions, they seem to indicate, that indeed even diffraction of sound -like light -may be handled as flow of particles. To avoid the feared explosion of computation time with higher order diffraction, a beam reunification may now be achieved by Quantized Pyramidal Beam Tracing.
This study investigates the usage of virtual acoustics in the framework of a research project dea... more This study investigates the usage of virtual acoustics in the framework of a research project dealing with the development of the binaural hearing aids and cochlear implants, with emphasis on the localisation of sound in different acoustical scenarios. Virtual acoustics allows the convolution of a measured head related transfer function (HRTF's) with the impulse response of a room generated by a computer model (using ODEON® software) to realistically simulate binaural sound. We report on (loud)speaker localization experiments conducted in a reverberant room, where eight listening subjects were asked to localize sound sources in the front horizontal plane. In the experiment, three different stimuli were used: high frequency sound around 3150 Hz, middle frequency sound in the 500 Hz band and the sound of a ringing telephone. The stimuli were played individually (1) from thirteen real loudspeakers, (2) as virtually 3D sounds via headphones, based on in situ binaural room impulse responses recorded by an artificial head, and (3) via headphones, as virtual sources simulated in ODEON® software (using HRTF receiver properties as measured on the artificial head). The results from the reverberant room are compared with listening tests performed in anechoic conditions with the same listening subjects.
On the basis of a statistical evaluation of the binaural sound source localization performance du... more On the basis of a statistical evaluation of the binaural sound source localization performance during listening tests by human subjects, we show that the convolution of a measured head-related transfer function (HRTF) with the room impulse response generated by a hybrid image source model with a stochastic scattering process using secondary sources
Proceedings of the National Academy of Sciences, 2010
Developmental dyslexia is characterized by severe reading and spelling difficulties that are pers... more Developmental dyslexia is characterized by severe reading and spelling difficulties that are persistent and resistant to the usual didactic measures and remedial efforts. It is well established that a major cause of these problems lies in poorly specified representations of speech sounds. One hypothesis states that this phonological deficit results from a more fundamental deficit in auditory processing. Despite substantial research effort, the specific nature of these auditory problems remains debated. A first controversy concerns the speech specificity of the auditory processing problems: Can they be reduced to more basic auditory processing, or are they specific to the perception of speech sounds? A second topic of debate concerns the extent to which the auditory problems are specific to the processing of rapidly changing temporal information or whether they encompass a broader range of complex spectrotemporal processing. By applying a balanced design with stimuli that were adequately controlled for acoustic complexity, we show that adults with dyslexia are specifically impaired at categorizing speech and nonspeech sounds that differ in terms of rapidly changing acoustic cues (i.e., temporal cues), but that they perform adequately when categorizing steady-state speech and nonspeech sounds. Thus, we show that individuals with dyslexia have an auditory temporal processing deficit that is not speech-specific. auditory processing | categorical perception | speech perception S peech contains a number of acoustic cues that are used to discriminate speech sounds belonging to different phonetic categories. For example, the acoustic cue that is critical for differentiating /bA/ versus /dA/, a stop consonant followed by a vowel, lies within the first 100 ms of the sounds, during which time the frequency of the second formant changes rapidly (i.e., a temporal cue). In contrast, the acoustic difference between two vowels such as /u/ versus /y/ lies in the frequency of the second formant, which stays relatively stable over time. Hence, an accurate perception of steady-state (i.e., nontemporal) spectral cues is essential for identification of these vowels. There is ample evidence that individuals with dyslexia exhibit problems in the representation of speech sounds (1), and that these may be rooted in a more fundamental auditory processing deficit (2). Originally, it was claimed that individuals with dyslexia have ad e ficit in processing auditory cues that are "temporal" in nature (i.e., rapidly changing), thereby causing problems in the accurate processing of rapid acoustic changes in speech (such as in stop consonants) (3). This speech perception problem was thought to consequently cause a cascade of effects, starting with the disruption of the normal development of the phonological system, eventually resulting in problems learning to read and spell. However, despite substantial research efforts, the literature is not concordant with respect to the specific nature of these auditory problems. In particular, it is unclear (i) whether the problem is specific to the perception of speech sounds (4) or whether it includes basic acoustic processing more generally , and (ii) whether the auditory problem is specific to rapid temporal processing (3, 5) or whether it encompasses a broader range of spectro-temporal processing abilities (6).
The etiology of developmental dyslexia remains widely debated. An appealing theory postulates tha... more The etiology of developmental dyslexia remains widely debated. An appealing theory postulates that the reading and spelling problems in individuals with dyslexia originate from reduced sensitivity to slow-rate dynamic auditory cues. This low-level auditory deficit is thought to provoke a cascade of effects, including inaccurate speech perception and eventually unspecified phoneme representations. The present study investigated sensitivity to frequency modulation and amplitude rise time, speech-in-noise perception and phonological awareness in 11-year-old children with dyslexia and a matched normal-reading control children. Group comparisons demonstrated that children with dyslexia were less sensitive than normal-reading children to slow-rate dynamic auditory processing, speech-in-noise perception, phonological awareness and literacy abilities. Correlations were found between slow-rate dynamic auditory processing and phonological awareness, and speech-in-noise perception and reading. Yet, no significant correlation between slow-rate dynamic auditory processing and speech-in-noise perception was obtained. Together, these results indicate that children with dyslexia have difficulties with slow-rate dynamic auditory processing and speech-in-noise perception and that these problems persist until sixth grade.
Amplitude modulations in the speech envelope are crucial elements for speech perception. These mo... more Amplitude modulations in the speech envelope are crucial elements for speech perception. These modulations comprise the processing rate at which syllabic (∼3-7 Hz), and phonemic transitions occur in speech. Theories about speech perception hypothesize that each hemisphere in the auditory cortex is specialized in analyzing modulations at different timescales, and that phonemic-rate modulations of the speech envelope lateralize to the left hemisphere, whereas right lateralization occurs for slow, syllabic-rate modulations. In the present study, neural processing of phonemic- and syllabic-rate modulations was investigated with auditory steady-state responses (ASSRs). ASSRs to speech-weighted noise stimuli, amplitude modulated at 4, 20, and 80 Hz, were recorded in 30 normal-hearing adults. The 80 Hz ASSR is primarily generated by the brainstem, whereas 20 and 4 Hz ASSRs are mainly cortically evoked and relate to speech perception. Stimuli were presented diotically (same signal to both ears) and monaurally (one signal to the left or right ear). For 80 Hz, diotic ASSRs were larger than monaural responses. This binaural advantage decreased with decreasing modulation frequency. For 20 Hz, diotic ASSRs were equal to monaural responses, while for 4 Hz, diotic responses were smaller than monaural responses. Comparison of left and right ear stimulation demonstrated that, with decreasing modulation rate, a gradual change from ipsilateral to right lateralization occurred. Together, these results (1) suggest that ASSR enhancement to binaural stimulation decreases in the ascending auditory system and (2) indicate that right lateralization is more prominent for low-frequency ASSRs. These findings may have important consequences for electrode placement in clinical settings, as well as for the understanding of low-frequency ASSR generation.
"Objectives: Speech intelligibility is strongly influenced by the ability to process temporal mod... more "Objectives: Speech intelligibility is strongly influenced by the ability to process temporal modulations. It is hypothesized that in dyslexia, deficient processing of rapidly-changing auditory information underlies a deficient development of phonological representations, causing reading and spelling problems. Low-frequency modulations between 4 and 20 Hz correspond to the processing rate of important phonological segments (syllables and phonemes respectively) in speech and therefore provide a bridge between low-level auditory and phonological processing. In the present study, temporal modulation processing was investigated by auditory steady state responses (ASSRs) in normal-reading and dyslexic adults.
Design: Multichannel ASSRs were recorded in normal-reading and dyslexic adults in response to speech-weighted noise stimuli amplitude modulated at 80 Hz, 20 Hz and 4 Hz. The 80 Hz modulation is known to be primarily generated by the brainstem, whereas the 20 Hz and 4 Hz modulations are mainly generated in the cortex. Furthermore, the 20 Hz and 4 Hz modulations provide an objective auditory performance measure related to phonemic-rate and syllabic-rate processing. In addition to neurophysiological measures, psychophysical tests of speech-in-noise perception and phonological awareness were assessed.
Results: Based on response-strength and phase coherence measures, normal-reading and dyslexic participants showed similar processing at the brainstem level. At the cortical level of the auditory system, dyslexic subjects demonstrated deviant phonemic-rate responses compared to normal readers, whereas no group differences were found for the syllabic-rate. Furthermore, a relation between phonemic-rate ASSRs and psychophysical tests of speech-in-noise perception and phonological awareness was obtained.
Conclusions: These results suggest reduced cortical processing for phonemic-rate modulations in dyslexic adults, presumably resulting in limited integration of temporal information in the dorsal phonological pathway."
The etiology of developmental dyslexia remains widely debated. An appealing theory postulates tha... more The etiology of developmental dyslexia remains widely debated. An appealing theory postulates that the reading and spelling problems in individuals with dyslexia originate from reduced sensitivity to slow-rate dynamic auditory cues. This low-level auditory deficit is thought to provoke a cascade of effects, including inaccurate speech perception and eventually unspecified phoneme representations. The present study investigated sensitivity to frequency modulation and amplitude rise time, speech-in-noise perception and phonological awareness in 11-year-old children with dyslexia and a matched normal-reading control children. Group comparisons demonstrated that children with dyslexia were less sensitive than normal-reading children to slow-rate dynamic auditory processing, speech-in-noise perception, phonological awareness and literacy abilities. Correlations were found between slow-rate dynamic auditory processing and phonological awareness, and speech-in-noise perception and reading. Yet, no significant correlation between slow-rate dynamic auditory processing and speech-in-noise perception was obtained. Together, these results indicate that children with dyslexia have difficulties with slow-rate dynamic auditory processing and speech-in-noise perception and that these problems persist until sixth grade.
Developmental dyslexia is characterized by severe reading and spelling difficulties that are pers... more Developmental dyslexia is characterized by severe reading and spelling difficulties that are persistent and resistant to the usual didactic measures and remedial efforts. It is well established that a major cause of these problems lies in poorly specified representations of speech sounds. One hypothesis states that this phonological deficit results from a more fundamental deficit in auditory processing. Despite substantial research effort, the specific nature of these auditory problems remains debated. A first controversy concerns the speech specificity of the auditory processing problems: Can they be reduced to more basic auditory processing, or are they specific to the perception of speech sounds?A second topic of debate concerns the extent to which the auditory problems are specific to the processing of rapidly changing temporal information or whether they encompass a broader range of complex spectrotemporal processing. By applying a balanced design with stimuli that were adequately controlled for acoustic complexity, we show that adults with dyslexia are specifically impaired at categorizing speech and nonspeech sounds that differ in terms of rapidly changing acoustic cues (i.e., temporal cues), but that they perform adequately when categorizing steady-state speech and nonspeech sounds. Thus, we show that individuals with dyslexia have an auditory temporal processing deficit that is not speech-specific.
Developmental dyslexia is characterized by severe reading and spelling difficulties that are pers... more Developmental dyslexia is characterized by severe reading and spelling difficulties that are persistent and resistant to the usual didactic measures and remedial efforts. It is well established that a major cause of these problems lies in poorly specified phonological representations. Many individuals with dyslexia also present impairments in auditory temporal processing and speech perception, but it remains debated whether these more basic perceptual impairments play a role in causing the reading problem. Longitudinal studies may help clarifying this issue by assessing preschool children before they receive reading instruction and by following them up through literacy development. The current longitudinal study shows impairments in auditory frequency modulation (FM) detection, speech perception and phonological awareness in kindergarten and in grade 1 in children who receive a dyslexia diagnosis in grade 3. FM sensitivity and speech-in-noise perception in kindergarten uniquely contribute to growth in reading ability, even after controlling for letter knowledge and phonological awareness. These findings indicate that impairments in auditory processing and speech perception are not merely an epiphenomenon of reading failure. Although no specific directional relations were observed between auditory processing, speech perception and phonological awareness, the highly significant concurrent and predictive correlations between all these variables suggest a reciprocal association and corroborate the evidence for the auditory deficit theory of dyslexia.
Diffusion tensor imaging tractography is a structural magnetic resonance imaging technique allowi... more Diffusion tensor imaging tractography is a structural magnetic resonance imaging technique allowing reconstruction and assessment of the integrity of three dimensional white matter tracts, as indexed by their fractional anisotropy. It is assumed that the left arcuate fasciculus plays a crucial role for reading development, as it connects two regions of the reading network, the left temporoparietal region and the left inferior frontal gyrus, for which atypical functional activation and lower fractional anisotropy values have been reported in dyslexic readers. In addition, we explored the potential role of the left inferior fronto-occipital fasciculus, which might connect a third region of the reading network, the left ventral occipitotemporal region with the left inferior frontal gyrus. In the present study, 20 adults with dyslexia and 20 typical reading adults were scanned using diffusion tensor imaging, and the bilateral arcuate fasciculus and the left inferior fronto-occipital fasciculus were delineated. Group comparisons show a significantly reduced fractional anisotropy in the left arcuate fasciculus of adults with dyslexia, in particular in the segment that directly connects posterior temporal and frontal areas. This fractional anisotropy reduction might reflect a lower degree of myelination in the dyslexic sample, as it co-occurred with a group difference in radial diffusivity. In contrast, no significant group differences in fractional anisotropy were found in the right arcuate fasciculus or in the left inferior fronto-occipital fasciculus. Correlational analyses (controlled for reading status) demonstrated a specific relation between performance on phoneme awareness and speech perception and the integrity of left arcuate fasciculus as indexed by fractional anisotropy, and between orthographic processing and fractional anisotropy values in left inferior fronto-occipital fasciculus. The present study reveals structural anomalies in the left arcuate fasciculus in adults with dyslexia. This finding corroborates current hypotheses of dyslexia as a disorder of network connections. In addition, our study demonstrates a correlational double dissociation, which might reflect neuroanatomical correlates of the dual route reading model: the left arcuate fasciculus seems to sustain the dorsal phonological route underlying grapheme-phoneme decoding, while the left inferior fronto-occipital fasciculus seems to sustain the ventral orthographic route underlying reading by direct word access.
Objective: Neonatal hearing screening programs in Flanders and the Netherlands use Natus ALGO scr... more Objective: Neonatal hearing screening programs in Flanders and the Netherlands use Natus ALGO screening devices. Since 2006 in Flanders and 2009 in the Netherlands, both programs have replaced the older ALGO Portable devices with the newer ALGO 3i devices. However, in both countries, ALGO 3i devices have a significantly higher rate of referrals than ALGO Portable devices. In Flanders, the refer rate has more than doubled with the switch to ALGO 3i devices. In the Netherlands, screening centers which used ALGO 3i devices also showed a significant increase in referrals. In both countries, the percentage of children diagnosed with permanent hearing loss remained approximately the same. Design: A technical comparison of both device types was carried out to identify possible causes for the increase in referrals. The stimulus output of two ALGO Portable and three ALGO 3i devices was recorded and analysed for stimulus level, spectral properties, and stimulus irregularities. Results: ALGO 3i devices stimulate at a peak level 4.6 dB lower than ALGO Portable devices, have a different stimulus spectrum and show unexplained stimulus irregularities during 4% of the stimulation time. Conclusions: A number of technical differences were found between both device types which could explain the increase in referrals.
The use of binaural pitch stimuli to test for the presence of binaural auditory impairment in rea... more The use of binaural pitch stimuli to test for the presence of binaural auditory impairment in reading-disabled subjects has so far led to contradictory outcomes. While some studies found that a majority of dyslexic subjects was unable to perceive binaural pitch, others obtained a clear response of dyslexic listeners to Huggins' pitch (HP). The present study clarified whether impaired binaural pitch perception is found in dyslexia. Results from a pitch contour identification test, performed in 31 dyslexic listeners and 31 matched controls, clearly showed that dyslexics perceived HP as well as the controls. Both groups also showed comparable results with a similar-sounding, but monaurally detectable, pitch-evoking stimulus. However, nine of the dyslexic subjects were found to have difficulty identifying pitch contours both in the binaural and the monaural conditions. The ability of subjects to correctly identify pitch contours was found to be significantly correlated to measures of frequency discrimination. This correlation may be attributed to the similarity of the experimental tasks and probably reflects impaired cognitive mechanisms related to auditory memory or auditory attention rather than impaired low-level auditory processing per se.
Diffusion tensor imaging tractography is a structural magnetic resonance imaging technique allowi... more Diffusion tensor imaging tractography is a structural magnetic resonance imaging technique allowing reconstruction and assessment of the integrity of three dimensional white matter tracts, as indexed by their fractional anisotropy. It is assumed that the left arcuate fasciculus plays a crucial role for reading development, as it connects two regions of the reading network, the left temporoparietal region and the left inferior frontal gyrus, for which atypical functional activation and lower fractional anisotropy values have been reported in dyslexic readers. In addition, we explored the potential role of the left inferior fronto-occipital fasciculus, which might connect a third region of the reading network, the left ventral occipitotemporal region with the left inferior frontal gyrus. In the present study, 20 adults with dyslexia and 20 typical reading adults were scanned using diffusion tensor imaging, and the bilateral arcuate fasciculus and the left inferior fronto-occipital fasciculus were delineated. Group comparisons show a significantly reduced fractional anisotropy in the left arcuate fasciculus of adults with dyslexia, in particular in the segment that directly connects posterior temporal and frontal areas. This fractional anisotropy reduction might reflect a lower degree of myelination in the dyslexic sample, as it co-occurred with a group difference in radial diffusivity. In contrast, no significant group differences in fractional anisotropy were found in the right arcuate fasciculus or in the left inferior fronto-occipital fasciculus. Correlational analyses (controlled for reading status) demonstrated a specific relation between performance on phoneme awareness and speech perception and the integrity of left arcuate fasciculus as indexed by fractional anisotropy, and between orthographic processing and fractional anisotropy values in left inferior fronto-occipital fasciculus. The present study reveals structural anomalies in the left arcuate fasciculus in adults with dyslexia. This finding corroborates current hypotheses of dyslexia as a disorder of network connections. In addition, our study demonstrates a correlational double dissociation, which might reflect neuroanatomical correlates of the dual route reading model: the left arcuate fasciculus seems to sustain the dorsal phonological route underlying grapheme-phoneme decoding, while the left inferior fronto-occipital fasciculus seems to sustain the ventral orthographic route underlying reading by direct word access.
Auditory processing problems in persons with dyslexia are still subject to debate, and one centra... more Auditory processing problems in persons with dyslexia are still subject to debate, and one central issue concerns the specific nature of the deficit. In particular, it is questioned whether the deficit is specific to speech and/or specific to temporal processing. To resolve this issue, a categorical perception identification task was administered in thirteen 11-year old dyslexic readers and 25 matched normal readers using 4 sound continua: (1) a speech contrast exploiting temporal cues (/bA/-/dA/), (2) a speech contrast defined by nontemporal spectral cues (/u/-/y/), (3) a nonspeech temporal contrast (spectrally rotated/ bA/-/da/), and (4) a nonspeech nontemporal contrast (spectrally rotated/u/-/y/). Results indicate that children with dyslexia are less consistent in classifying speech and nonspeech sounds on the basis of rapidly changing (i.e., temporal) information whereas they are unimpaired in steady-state speech and nonspeech sounds. The deficit is thus restricted to categorizing sounds on the basis of temporal cues and is independent of the speech status of the stimuli. The finding of a temporal-specific but not speech-specific deficit in children with dyslexia is in line with findings obtained in adults using the same paradigm (Vandermosten et al., 2010, Proceedings of the National Academy of Sciences of the United States of America, 107: 10389–10394). Comparison of the child and adult data indicates that the consistency of categorization considerably improves between late childhood and adulthood, particularly for the continua with temporal cues. Dyslexic and normal readers show a similar developmental progress with the dyslexic readers lagging behind both in late childhood and in adulthood.
Objectives: Speech intelligibility is strongly influenced by the ability to process temporal modu... more Objectives: Speech intelligibility is strongly influenced by the ability to process temporal modulations. It is hypothesized that in dyslexia, deficient processing of rapidly changing auditory information underlies a deficient development of phonological representations, causing reading and spelling problems. Low-frequency modulations between 4 and 20 Hz correspond to the processing rate of important phonological segments (syllables and phonemes, respectively) in speech and therefore provide a bridge between low-level auditory and phonological processing. In the present study, temporal modulation processing was investigated by auditory steady state responses (ASSRs) in normalreading and dyslexic adults.
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Papers by Jan Wouters
Design: Multichannel ASSRs were recorded in normal-reading and dyslexic adults in response to speech-weighted noise stimuli amplitude modulated at 80 Hz, 20 Hz and 4 Hz. The 80 Hz modulation is known to be primarily generated by the brainstem, whereas the 20 Hz and 4 Hz modulations are mainly generated in the cortex. Furthermore, the 20 Hz and 4 Hz modulations provide an objective auditory performance measure related to phonemic-rate and syllabic-rate processing. In addition to neurophysiological measures, psychophysical tests of speech-in-noise perception and phonological awareness were assessed.
Results: Based on response-strength and phase coherence measures, normal-reading and dyslexic participants showed similar processing at the brainstem level. At the cortical level of the auditory system, dyslexic subjects demonstrated deviant phonemic-rate responses compared to normal readers, whereas no group differences were found for the syllabic-rate. Furthermore, a relation between phonemic-rate ASSRs and psychophysical tests of speech-in-noise perception and phonological awareness was obtained.
Conclusions: These results suggest reduced cortical processing for phonemic-rate modulations in dyslexic adults, presumably resulting in limited integration of temporal information in the dorsal phonological pathway."
auditory temporal processing deficit that is not speech-specific.
Design: A technical comparison of both device types was carried out to identify possible causes for the increase in referrals. The stimulus output of two ALGO Portable and three ALGO 3i devices was recorded and analysed for stimulus level, spectral properties, and stimulus irregularities.
Results: ALGO 3i devices stimulate at a peak level 4.6 dB lower than ALGO Portable devices, have a different stimulus spectrum and show unexplained stimulus irregularities during 4% of the stimulation time.
Conclusions: A number of technical differences were found between both device types which could explain the increase in referrals.
Design: Multichannel ASSRs were recorded in normal-reading and dyslexic adults in response to speech-weighted noise stimuli amplitude modulated at 80 Hz, 20 Hz and 4 Hz. The 80 Hz modulation is known to be primarily generated by the brainstem, whereas the 20 Hz and 4 Hz modulations are mainly generated in the cortex. Furthermore, the 20 Hz and 4 Hz modulations provide an objective auditory performance measure related to phonemic-rate and syllabic-rate processing. In addition to neurophysiological measures, psychophysical tests of speech-in-noise perception and phonological awareness were assessed.
Results: Based on response-strength and phase coherence measures, normal-reading and dyslexic participants showed similar processing at the brainstem level. At the cortical level of the auditory system, dyslexic subjects demonstrated deviant phonemic-rate responses compared to normal readers, whereas no group differences were found for the syllabic-rate. Furthermore, a relation between phonemic-rate ASSRs and psychophysical tests of speech-in-noise perception and phonological awareness was obtained.
Conclusions: These results suggest reduced cortical processing for phonemic-rate modulations in dyslexic adults, presumably resulting in limited integration of temporal information in the dorsal phonological pathway."
auditory temporal processing deficit that is not speech-specific.
Design: A technical comparison of both device types was carried out to identify possible causes for the increase in referrals. The stimulus output of two ALGO Portable and three ALGO 3i devices was recorded and analysed for stimulus level, spectral properties, and stimulus irregularities.
Results: ALGO 3i devices stimulate at a peak level 4.6 dB lower than ALGO Portable devices, have a different stimulus spectrum and show unexplained stimulus irregularities during 4% of the stimulation time.
Conclusions: A number of technical differences were found between both device types which could explain the increase in referrals.