Heleen Luts

Preschool impairments in auditory processing and speech perception uniquely predict future reading problems

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.

Adults with dyslexia are impaired in categorizing speech and nonspeech sounds on the basis of temporal cues

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 spectro-temporal 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.

Clinical application of dichotic multiple-stimulus auditory steady-state responses in high-risk newborns and young children

Experience with dichotic multiple-stimulus auditory steady-state responses (ASSRs) in clinical practice is described. ASSR thresholds were assessed in a sample of 60 high-risk newborns and young children between birth and 4 years of age. Amplitudes and signal-to-noise ratios (SNRs) of the ASSR were compared between normal-hearing infants and adults. Age-related changes within a group of infants younger than 3 months of age were investigated. A comparison was made between ASSR, the click-evoked auditory brainstem response and behavioral hearing thresholds in infants with a wide range of hearing threshold levels. Mean ASSR thresholds for normal-hearing infants at an average corrected age of 12 days were 42 ± 10, 35 ± 10, 32 ± 10 and 36 ± 9 dB SPL for 0.5, 1, 2 and 4 kHz, respectively. Compared to adults, these thresholds were elevated by on average 11 dB and SNRs were 1.7 times smaller. However, based on ASSRs, reasonably accurate estimations could be made of behavioral hearing thresholds obtained at a later age (median delay of 7 months). The predicted thresholds were in 61% of the cases within 10 dB of the corresponding behavioral thresholds, and in 83% of the cases within 15 dB. In less than 1 h, thresholds at four frequencies per ear could be obtained. The optimal age of testing is between 1 week and 3 months corrected age. The dichotic multiple-stimulus ASSR technique is a valuable extension of the clinical test battery for hearing-impaired children, as a follow-up diagnostic after the neonatal hearing screening.

Impairments in speech and nonspeech sound categorization in children with dyslexia are driven by temporal processing difficulties

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.

Hearing assessment by recording multiple auditory steady-state responses: the influence of test duration

The influence of test duration on the precision of hearing thresholds estimated by recording multiple auditory steady-state responses (ASSRs) was investigated. ASSR thresholds at four frequencies in both ears were assessed in 10 normal-hearing and 10 hearing-impaired subjects. The precision of the estimated hearing thresholds was compared for ASSR recordings of 5, 10 and 15 min per intensity level, corresponding to total test durations of approximately 30, 55 and 70 min for hearing-impaired ears. Furthermore, an intensity step size of 10 dB was compared to a step size of 5 dB. The mean difference scores averaged over the four frequencies were 15±10, 12±9 and 11±8 dB after recordings of 5, 10 and 15 min respectively. The corresponding Pearson correlation coefficients were 0.93, 0.95 and 0.96. Increasing the length of the separate recordings increases the precision of the estimates, independent of tested frequency. A compromise between both will have to be made. With a total test duration of approximately 1 h, four hearing thresholds in both ears can be estimated with a standard error of the estimate of 8dB. Sumario Se investigó la influencia de la duración de la prueba en la precisión de umbrales auditivos estimados por medio del registro múltiple de respuestas de estado estable (ASSRs). Se evaluaron los umbrales ASSR en cuatro frecuencias en ambos oídos de 10 normo-oyentes y 10 hipoacúsicos. La precisión de los umbrales auditivos estimados se comparó con los registros ASSR de 5, 10 y 15 minutos por nivel de intensidad, correspondiendo a duraciones totales de las pruebas de aproximadamente 30, 55 y 70 minutos en oídos hipoacúsicos. Incluso se compararon los intervalos de intensidad de 10 dB con los de 5 dB. La diferencia media de puntuaciones promediadas en las cuatro frecuencias fueron de 15±10, 12±9 y 11±8dB después de los registros de 5, 10 y 15 minutos, respectivamente. Los correspondientes coeficientes de correlación de Pearson fueron de 0.93, 0.95 y 0.96. El aumento en la duración de los registros separados aumenta la precisión de las estimaciones, independientemente de la frecuencia evaluada. Deberá establecerse un compromiso entre ambos. Con una duración total de la prueba de una hora se pueden estimar cuatro umbrales auditivos en ambos oídos con un error estándar de 8dB.

Reduced sensitivity to slow-rate dynamic auditory information in children with dyslexia

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.

Comparison of three types of French speech­in­noise tests: A multi­center study

Abstract Objective: To compare results on the everyday sentence test ‘FIST’, the new closed-set sentence test ‘FrMatrix’, and the digit triplet screening test ‘FrDigit3’. Design: First, the FrMatrix was developed and normative values were obtained. Subsequently, speech reception thresholds (SRTs) for the three types of tests were gathered at four study centers representing different geographic regions in Belgium and France. Study sample: Fifty-seven normal-hearing listeners took part in the normative study of the FrMatrix, and 118 subjects, with a wide range of hearing thresholds, participated in the comparative study. Results: Homogenizing the individual words of the FrMatrix with regard to their intelligibility resulted in a reference SRT of −6.0 (±0.6) dB SNR and slope at the SRT of 14.0 %/dB. The within-subject variability was only 0.4 dB. Comparison of the three tests showed high correlations between the SRTs mutually (>0.81). The FrMatrix had the highest discriminative power, both in stationary and in fluctuating noise. For all three tests, differences across the participating study centers were small and not significant. Conclusions: The FIST, the FrMatrix, and the FrDigit3 provide similar results and reliably evaluate speech recognition performance in noise both in normal-hearing and hearing-impaired listeners.

The French digit triplet test: A hearing screening tool for speech intelligibility in noise

Abstract A French speech intelligibility screening test in noise that applies digit triplets as stimuli has been developed and evaluated for both telephone and broadband headphone use. After optimizing the speech material based on the intelligibility of the individual digits, norms for normal-hearing subjects were established. speech reception thresholds (SRTs) of −6.4 ± 0.4 and −10.5 ± 0.3 dB SNR, and slopes of 17.1 and 27.1 %/dB were obtained for telephone and broadband headphone presentation, respectively. The French digit triplet test by telephone was then implemented as an automatic self-screening test by home telephone, and further evaluated in normal-hearing and hearing-impaired listeners. A test-retest variability of 0.7 dB was found and the correlation between SRT and pure-tone average (PTA0.5,1,2,4) was 0.77. One month after launching the test, 20 000 calls were registered. It can be concluded that both versions of the newly developed test have steep slopes and small SRT differences across normal-hearing listeners. The screening test by telephone is highly reliable and proves to fulfill the need for an easily accessible and objective hearing screening. Sumario Se desarrolló y evaluó una prueba de tamiz de inteligibilidad del lenguaje en ruido, utilizando ternas de dígitos como estímulo, tanto para teléfono como para auriculares de banda ancha. Después de optimizar el material lingüístico basado en la inteligibilidad de los dígitos individuales, se establecieron las normas para los sujetos normoyentes. Se obtuvieron umbrales de recepción del lenguaje (SRTs) de -6.4 ± 0.4 y -10.5 ± 0.3dB SNR y pendientes de 17.1 y 27.1%/dB para teléfono y auriculares de banda ancha, respectivamente. Se implementó la prueba de terna de dígitos en francés por teléfono como una prueba de tamiz autoaplicable por teléfono en casa y después se evaluó en normoyentes e hipoacúsicos. Se encontró una variabilidad de test-re-test de 0.7 dB y la correlación entre SRT y el promedio de tonos puros (PTA0.5,1,2,4) fue de 0.77. Un mes después de lanzar la prueba, se registraron 20,000 llamadas. Se puede concluir que ambas versiones de la prueba recientemente desarrollada tiene pendientes pronunciadas y pequeñas diferencias del SRT entre los normoyentes. La prueba de tamiz por teléfono es altamente confiable y demuestra que satisface las necesidades de una prueba de tamiz auditivo fácil, accesible y objetiva.

Comparison of MASTER and AUDERA for measurement of auditory steady-state responses.

Two approaches to assess auditory steady-state responses (ASSR) are compared under similar test conditions: a monaural single-frequency technique with a detection method based on phase coherence (AUDERA), and a binaural multiple-frequency technique using the F-test (MASTER). ASSR thresholds at four frequencies were assessed with both methods in both ears of ten normal-hearing and ten hearing-impaired adult subjects, within a test duration of one hour. The test-retest reliability and the influence of prolonging the test duration are assessed. For the total subject group the multiple-frequency technique outperforms the single-frequency technique. In hearing-impaired subjects, however, both techniques perform equally well. Hearing thresholds can be estimated with a standard error of the estimate between 7 and 12 dB dependent on frequency. About 55% of the estimates are within 5 dB of the behavioral hearing threshold, and 94% within 15 dB. Prolonging the test duration improves the performance of both techniques.

Auditory steady state cortical responses indicate deviant phonemic-rate processing in adults with dyslexia

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, 20, and 4 Hz. The 80 Hz modulation is known to be primarily generated by the brainstem, whereas the 20 and 4 Hz modulations are mainly generated in the cortex. Furthermore, the 20 and 4 Hz modulations provide an objective auditory performance measure related to phonemic- and syllabic-rate processing. In addition to neurophysiological measures, psychophysical tests of speech-in-noise perception and phonological awareness were assessed. Results: On the basis of 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 with normal readers, whereas no group differences were found for the syllabic rate. Furthermore, a relationship between phonemic-rate ASSRs and psychophysical tests of speech-in-noise perception and phonological awareness was obtained. Conclusions: The 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.