Auditory Evoked Potential Patterns to Voiced and Voiceless Speech Sounds in Adult Developmental Dyslexics with Persistent Deficits

Speech-Brain Frequency Entrainment of Dyslexia with and without Phonological Deficits

Developmental dyslexia is a cognitive disorder characterized by difficulties in linguistic processing. Our purpose is to distinguish subtypes of developmental dyslexia by the level of speech–EEG frequency entrainment (δ: 1–4; β: 12.5–22.5; γ1: 25–35; and γ2: 35–80 Hz) in word/pseudoword auditory discrimination. Depending on the type of disabilities, dyslexics can divide into two subtypes—with less pronounced phonological deficits (NoPhoDys—visual dyslexia) and with more pronounced ones (PhoDys—phonological dyslexia). For correctly recognized stimuli, the δ-entrainment is significantly worse in dyslexic children compared to controls at a level of speech prosody and syllabic analysis. Controls and NoPhoDys show a stronger δ-entrainment in the left-hemispheric auditory cortex (AC), anterior temporal lobe (ATL), frontal, and motor cortices than PhoDys. Dyslexic subgroups concerning normolexics have a deficit of δ-entrainment in the left ATL, inferior frontal gyrus (IFG), and the right AC. PhoDys has higher δ-entrainment in the posterior part of adjacent STS regions than NoPhoDys. Insufficient low-frequency β changes over the IFG, the inferior parietal lobe of PhoDys compared to NoPhoDys correspond to their worse phonological short-term memory. Left-dominant 30 Hz-entrainment for normolexics to phonemic frequencies characterizes the right AC, adjacent regions to superior temporal sulcus of dyslexics. The pronounced 40 Hz-entrainment in PhoDys than the other groups suggest a hearing “reassembly” and a poor phonological working memory. Shifting up to higher-frequency γ-entrainment in the AC of NoPhoDys can lead to verbal memory deficits. Different patterns of cortical reorganization based on the left or right hemisphere lead to differential dyslexic profiles.

Language Experience with a Native-Language Phoneme Sequence Modulates the Effects of Attention on Cortical Sensory Processing

Auditory evoked potentials (AEP) reflect spectro-temporal feature changes within the spoken word and are sufficiently reliable to probe deficits in auditory processing. The current research assessed whether attentional modulation would alter the morphology of these AEPs and whether native-language experience with phoneme sequences would influence the effects of attention. Native-English and native-Polish adults listened to nonsense word pairs that contained the phoneme sequence onsets /st/, /sət/, /pət/ that occur in both the Polish and English languages and the phoneme sequence onset /pt/ that occurs in the Polish language, but not the English language. Participants listened to word pairs within two experimental conditions designed to modulate attention. In one condition, participants listened to word pairs and performed a behavioral task to the second word in the pairs (“with task”) and in the alternate condition participants listened to word pairs without performing a task (“without task”). Conditions were counterbalanced so that half the English and Polish subjects performed the “without task” condition as the first testing session and the “with task” condition as the second testing session. The remaining English and Polish subjects performed the tasks in the reverse order. Two or more months separated the testing sessions. Task conditions did not modulate the morphology of the AEP. Attention, however, modulated the AEP by producing a negative shift in the overall waveform. This effect of attention was modulated by experience with a native-language phoneme sequence. Thus, only Polish listeners showed an effect of attention to the native language /pt/ onset when the behavioral task occurred as the second testing session for which attention demands were reduced. This effect began at 400 ms and suggests a mechanism at intermediate stages within auditory cortex that facilitates recognition of the native language for comprehension.

Stability of the Cortical Sensory Waveforms, the P1-N1-P2 Complex and T-Complex, of Auditory Evoked Potentials

Purpose

Atypical cortical sensory waveforms reflecting impaired encoding of auditory stimuli may result from inconsistency in cortical response to the acoustic feature changes within spoken words. Thus, the present study assessed intrasubject stability of the P1-N1-P2 complex and T-complex to multiple productions of spoken nonwords in 48 adults to provide benchmarks for future studies probing auditory processing deficits.

Method

Response trials were split (split epoch averages) for each of 4 word types for each subject and compared for similarity in waveform morphology. Waveform morphology association was assessed between 50 and 600 ms, the time frame reflecting spectro-temporal feature processing for the stimuli used in the study.

Results

Using approximately 70 trials in each split epoch, the P1-N1-P2 complex was found to be highly stable, with high positive associations found for all subjects for at least 3 word types. The T-complex was more variable, with high positive associations found for all subjects to at least 1 word type.

Conclusions

The P1-N1-P2 split epochs at group and individual levels and the T-complex at group level can be used to assess consistency of neural response in individuals with auditory processing deficits. The T-complex relative to the P1-N1-P2 complex in individuals can provide information pertaining to phonological processing.

Vowels and Consonants in the Brain: Evidence from Magnetoencephalographic Studies on the N1m in Normal-Hearing Listeners

Speech sound perception is one of the most fascinating tasks performed by the human brain. It involves a mapping from continuous acoustic waveforms onto the discrete phonological units computed to store words in the mental lexicon. In this article, we review the magnetoencephalographic studies that have explored the timing and morphology of the N1m component to investigate how vowels and consonants are computed and represented within the auditory cortex. The neurons that are involved in the N1m act to construct a sensory memory of the stimulus due to spatially and temporally distributed activation patterns within the auditory cortex. Indeed, localization of auditory fields maps in animals and humans suggested two levels of sound coding, a tonotopy dimension for spectral properties and a tonochrony dimension for temporal properties of sounds. When the stimulus is a complex speech sound, tonotopy and tonochrony data may give important information to assess whether the speech sound parsing and decoding are generated by pure bottom-up reflection of acoustic differences or whether they are additionally affected by top-down processes related to phonological categories. Hints supporting pure bottom-up processing coexist with hints supporting top-down abstract phoneme representation. Actually, N1m data (amplitude, latency, source generators, and hemispheric distribution) are limited and do not help to disentangle the issue. The nature of these limitations is discussed. Moreover, neurophysiological studies on animals and neuroimaging studies on humans have been taken into consideration. We compare also the N1m findings with the investigation of the magnetic mismatch negativity (MMNm) component and with the analogous electrical components, the N1 and the MMN. We conclude that N1 seems more sensitive to capture lateralization and hierarchical processes than N1m, although the data are very preliminary. Finally, we suggest that MEG data should be integrated with EEG data in the light of the neural oscillations framework and we propose some concerns that should be addressed by future investigations if we want to closely line up language research with issues at the core of the functional brain mechanisms.

Representation of spectro-temporal features of spoken words within the P1-N1-P2 and T-complex of the auditory evoked potentials (AEP)

The purpose of the study was to determine whether P1-N1-P2 and T-complex morphology reflect spectro-temporal features within spoken words that approximate the natural variation of a speaker and whether waveform morphology is reliable at group and individual levels, necessary for probing auditory deficits. The P1-N1-P2 and T-complex to the syllables /pət/ and /sət/ within 70 natural word productions each were examined. EEG was recorded while participants heard nonsense word pairs and performed a syllable identification task to the second word in the pairs. Single trial auditory evoked potentials (AEP) to the first words were analyzed. Results found P1-N1-P2 and T-complex to reflect spectral and temporal feature processing. Also, results identified preliminary benchmarks for single trial response variability for individual subjects for sensory processing between 50 and 600ms. P1-N1-P2 and T-complex, at least at group level, may serve as phenotypic signatures to identify deficits in spectro-temporal feature recognition and to determine area of deficit, the superior temporal plane or lateral superior temporal gyrus.

Objective measurement of high-level auditory cortical function in children

OBJECTIVE

This study examined whether the N2 latency of the cortical auditory evoked potential (CAEP) could be used as an objective indicator of temporal processing ability in normally hearing children.

METHODS

The N2 latency was evoked using three temporal processing paradigms: (1) differences in voice-onset-times (VOTs); (2) speech-in-noise using the CV/da/embedded in broadband noise (BBN) with varying signal-to-noise ratios (SNRs); and (3) 16Hz amplitude-modulated (AM) BBN presented (i) alone and (ii) following an unmodulated BBN, using four modulation depths. Thirty-four school-aged children with normal hearing, speech, language and reading were stratified into two groups: 5-7 years (n=13) and 8-12 years (n=21).

RESULTS

The N2 latency shifted significantly and systematically with differences in VOT and SNR, and was significantly different in the two AM-BBN conditions.

CONCLUSIONS

For children without an N1 peak in the cortical waveform, the N2 peak can be used as a sensitive measure of temporal processing for these stimuli.

SIGNIFICANCE

N2 latency of the CAEP can be used as an objective measure of temporal processing ability in a paediatric population with temporal processing disorder who are difficult to assess via behavioural response.

Modulation of pre-attentive spectro-temporal feature processing in the human auditory system by HD-tDCS

The present study examined the functional lateralization of the human auditory cortex (AC) for pre-attentive spectro-temporal feature processing. By using high-definition transcranial direct current stimulation (HD-tDCS), we systematically modulated neuronal activity of the bilateral AC. We assessed the influence of anodal and cathodal HD-tDCS delivered over the left or right AC on auditory mismatch negativity (MMN) in response to temporal as well as spectral deviants in 12 healthy subjects. The results showed that MMN to temporal deviants was significantly enhanced by anodal HD-tDCS applied over the left AC only. Our data indicate a left hemispheric dominance for the pre-attentive processing of low-level temporal information.

A review of the neurobiological basis of dyslexia in the adult population

INTRODUCTION

Adult dyslexia affects about 4% of the population. However, studies on the neurobiological basis of dyslexia in adulthood are scarce compared to paediatric studies.

AIM

This review investigates the neurobiological basis of dyslexia in adulthood.

DEVELOPMENT

Using PsycINFO, a database of psychology abstracts, we identified 11 studies on genetics, 9 neurostructural studies, 13 neurofunctional studies and 24 neurophysiological studies. Results from the review show that dyslexia is highly heritable and displays polygenic transmission. Likewise, adult neuroimaging studies found structural, functional, and physiological changes in the parieto-occipital and occipito-temporal regions, and in the inferior frontal gyrus, in adults with dyslexia.

CONCLUSION

According to different studies, aetiology in cases of adult dyslexia is complex. We stress the need for neurobiological studies of dyslexia in languages with transparent spelling systems.

Dyslexia

Developmental dyslexia (DD) is a specific and persistent disability affecting the acquisition of written language. Prevalence is estimated to be between 5% and 17% of school-aged children; it therefore represents a major public health issue. Neurological in origin, its causes are unknown, although there is a clear genetic component. Diagnosis rests upon the use of standardized tests and tools to assess reading and spelling, as well as phonological skills. The importance of early diagnosis cannot be overemphasized and much current research is focusing on screening and prediction, particularly through use of objective imaging techniques (e.g., EEG/MEG), which have implicated cortical abnormalities in central auditory processing (Giraud et al., 2005, 2008). Remediation should be intensive, begin as early as possible, and be tailored to the individual. Phonics based treatments are most effective and several variants, incorporating temporal auditory, articulatory, or multisensory training exercises, have been developed or proposed. Clinical improvements in phonological skills and reading with such treatments have been shown to correlate with changes in the brains of dyslexic children in several functional imaging studies.

Gaps-in-noise (GIN©) test results in children with and without reading disabilities and phonological processing deficits

OBJECTIVE

To determine if the gaps-in-noise (GIN(©)) test could differentiate children with dyslexia and significant phonological awareness deficits from a group of children with normal reading skills.

DESIGN

A prospective study of GIN test performance in two groups of children. Participants were administered routine audiological tests, a phonological processing test, and an auditory temporal resolution test (GIN test). Statistical testing was completed to determine if significant differences existed between groups on GIN test results and phonological processing measures, and to examine potential relationships between these test measures. Routine clinical analysis procedures examined the performance of the two groups from a clinical perspective.

STUDY SAMPLE

Participants included 61 children between the ages of 8 years, 1 month and 9 years, 11 months, separated into two groups: children with dyslexia and significant phonological deficits (Group I); normal-reading peers with age-appropriate phonological skills (Group II).

RESULTS

Children in Group I showed longer gap detection (GD) thresholds and lower gap identification scores than did the children in Group II. Results of statistical and clinical testing revealed significant differences between the groups.

CONCLUSION

An auditory temporal processing deficit is a factor to be considered in children presenting with dyslexia and phonological processing disorders.

Universality of categorical perception deficit in developmental dyslexia: an investigation of Mandarin Chinese tones

BACKGROUND

While previous studies have shown that children affected by dyslexia exhibit a deficit in categorical perception of segmental features in alphabetic languages, it remains unclear whether the categorical perception deficit generalizes to nonalphabetic languages at the suprasegmental level. In this study, we investigated the occurrence of categorical perception deficit in Mandarin lexical tones in Chinese children with dyslexia.

METHODS

Both behavioral and electrophysiological measures were taken to compare Chinese dyslexic children with age-matched controls. Auditory event-related potentials were collected with a passive listening oddball paradigm.

RESULTS

Behavioral data showed that dyslexic children perceived lexical tone contrasts less categorically and less precisely than age-matched controls. Consistent with the behavioral data, the across-category tone contrast elicited larger mismatch negativity than the within-category distinction in the left hemisphere for the age-matched controls but not for the dyslexic children.

CONCLUSION

The behavioral and electrophysiological results demonstrate impaired categorical perception of lexical tones in Chinese children with dyslexia. Our findings support the hypothesis that children affected by dyslexia have a general deficit in categorical perception of speech, which generalizes to nonalphabetic languages at the suprasegmental level.

Effects of consonant-vowel transitions in speech stimuli on cortical auditory evoked potentials in adults

We examined the neural activation to consonant-vowel transitions by cortical auditory evoked potentials (AEPs). The aim was to show whether cortical response patterns to speech stimuli contain components due to one of the temporal features, the voice-onset time (VOT). In seven normal-hearing adults, the cortical responses to four different monosyllabic words were opposed to the cortical responses to noise stimuli with the same temporal envelope as the speech stimuli. Significant hemispheric asymmetries were found for speech but not in noise evoked potentials. The difference signals between the AEPs to speech and corresponding noise stimuli revealed a significant negative component, which correlated with the VOT. The hemispheric asymmetries can be referred to rapid spectral changes. The correlation with the VOT indicates that the significant component in the difference signal reflects the perception of the acoustic change within the consonant-vowel transition. Thus, at the level of automatic processing, the characteristics of speech evoked potentials appear to be determined primarily by temporal aspects of the eliciting stimuli.

Common and distinct neural substrates for the perception of speech rhythm and intonation

The present study examines the neural substrates for the perception of speech rhythm and intonation. Subjects listened passively to synthesized speech stimuli that contained no semantic and phonological information, in three conditions: (1) continuous speech stimuli with fixed syllable duration and fundamental frequency in the standard condition, (2) stimuli with varying vocalic durations of syllables in the speech rhythm condition, and (3) stimuli with varying fundamental frequency in the intonation condition. Compared to the standard condition, speech rhythm activated the right middle superior temporal gyrus (mSTG), whereas intonation activated the bilateral superior temporal gyrus and sulcus (STG/STS) and the right posterior STS. Conjunction analysis further revealed that rhythm and intonation activated a common area in the right mSTG but compared to speech rhythm, intonation elicited additional activations in the right anterior STS. Findings from the current study reveal that the right mSTG plays an important role in prosodic processing. Implications of our findings are discussed with respect to neurocognitive theories of auditory processing.

Enhanced physiologic discriminability of stop consonants with prolonged formant transitions in awake monkeys based on the tonotopic organization of primary auditory cortex

Many children with specific language impairment (SLI) have difficulty in perceiving stop consonant-vowel syllables (e.g., /ba/, /ga/, /da/) with rapid formant transitions, but perform normally when formant transitions are extended in time. This influential observation has helped lead to the development of the auditory temporal processing hypothesis, which posits that SLI is causally related to the processing of rapidly changing sounds in aberrantly expanded windows of temporal integration. We tested a potential physiological basis for this observation by examining whether syllables varying in their consonant place of articulation (POA) with prolonged formant transitions would evoke better differentiated patterns of activation along the tonotopic axis of A1 in awake monkeys when compared to syllables with short formant transitions, especially for more prolonged windows of temporal integration. Amplitudes of multi-unit activity evoked by /ba/, /ga/, and /da/ were ranked according to predictions based on responses to tones centered at the spectral maxima of frication at syllable onset. Population responses representing consonant POA were predicted by the tone responses. Predictions were stronger for syllables with prolonged formant transitions, especially for longer windows of temporal integration. Relevance of findings to normal perception and that occurring in SLI are discussed.

Low-level defective processing of non-verbal sounds in dyslexic children

We compared processing of non-verbal auditory stimuli by dyslexic and non-dyslexic children using electrophysiological methods. The study included 39 children (17 with dyslexia plus 22 controls) assessed via frontal, central, parietal, and temporal electrodes. As an extension of previous P300 event-related potential studies, we analysed variations in the power values of 40-Hz oscillations (gamma-band oscillations involved in cognitive processing) during a specific time window in response to the auditory 'oddball' paradigm that entail target (random 2 kHz) and standard (frequent 1 kHz) stimuli. Dyslexic children differed significantly from controls (P<0.001) in the mean power of the wavelet-transformed 40-Hz oscillation in a time interval starting at 25 ms after stimulus onset up to 50 ms. This means defective processing of sounds. Within groups, standard and target tones elicited significantly different power values (P<0.001). Correlations of values between standard and target responses at each electrode position were not significant within either group, although dyslexics showed a lower correlation than controls. Significant differences in the mean power of these oscillations detected at very early stages of auditory processing in dyslexic children and the wide range of mean values reveal impairment in processing non-verbal sounds in dyslexia. Our results also support recent findings using behavioural and electrophysiological methods suggesting that dyslexia is a general auditory deficit instead of a speech-specific deficit.

Topography of syllable change-detection electrophysiological indices in children and adults with reading disabilities

INTRODUCTION

Developmental dyslexia (DD) is a frequent language-based learning disorder. The predominant etiological view postulates that reading problems originate from a phonological impairment.

METHOD

We studied mismatch negativity (MMN) and Late Discriminative Negativity (LDN) to syllables change in both children (n=12; 8-12 years) and young adults (n=15; 14-23 years) with DD compared with controls.

RESULTS/DISCUSSION

The present study confirmed abnormal automatic discrimination of syllable changes in both children and adults with developmental dyslexia. MMN topographic, amplitude and latency group differences were evidenced, suggesting different brain mechanisms involved in elementary auditory stimulus change-detection in DD, especially in the left hemisphere. The LDN results demonstrated that the auditory disorder of temporal processing in DD children becomes more serious at late stages of information processing and that the apparent cerebral hypo reactivity to speech changes in DD actually may correspond to additional processes. The age-related differences observed in both MMN and LDN topographies, amplitudes and latency between subjects with DD and controls could indicate different developmental courses in the neural representation of basic speech sounds in good and poor readers, with a tendency to normalization with increasing age.

CONCLUSION

Our results showing atypical electrophysiological concomitants of speech auditory perception in DD strongly support the hypothesis of deviant cortical organization in DD.

The representation of voice onset time in the cortical auditory evoked potentials of young children

OBJECTIVE

The aim of this study was to determine whether, in young children, a cortical neurophysiologic representation of the voicing status of a stop consonant could be found in the absence of the N1 component in the cortical auditory evoked potential (CAEP). In adults, a 'double-on' N1 response is often considered a cortical marker of VOT representation.

METHODS

Scalp-recorded CAEPs were measured from six electrode sites in 10 children aged 4-8 years in response to a /da/-/ta/ continuum in which voice onset times (VOTs) varied from 0 to 60ms. CAEPs were also recorded from C(z) in a group of eight children aged 2-3 years in response to stimuli with VOTs of 0 and 60ms.

RESULTS

Cortical evoked responses elicited by stimuli with VOT values ranging from 0 to 60ms (i.e., by stimuli perceived as /da/ and /ta/) were similar in morphology. There was no evidence of a 'double-on' morphology for stimuli with long VOTs. However, latency changes in the P1 and N2 components were observed as a function of VOT changes.

CONCLUSIONS

Our results demonstrate that a representation of VOT, as recorded by scalp electrodes, exists in the developing cortical evoked response, but that representation is different than that in the adult response. The results describe the developmental changes in cortical representation of VOT in children ages 2-8 years.

SIGNIFICANCE

The child's CAEP reflects physiologic processes, which are involved in the cortical encoding of VOT. Overall, cortical representation of VOT in children ages 2-8 is different than in adults.

Electrical brain imaging evidences left auditory cortex involvement in speech and non-speech discrimination based on temporal features

BACKGROUND

Speech perception is based on a variety of spectral and temporal acoustic features available in the acoustic signal. Voice-onset time (VOT) is considered an important cue that is cardinal for phonetic perception.

METHODS

In the present study, we recorded and compared scalp auditory evoked potentials (AEP) in response to consonant-vowel-syllables (CV) with varying voice-onset-times (VOT) and non-speech analogues with varying noise-onset-time (NOT). In particular, we aimed to investigate the spatio-temporal pattern of acoustic feature processing underlying elemental speech perception and relate this temporal processing mechanism to specific activations of the auditory cortex.

RESULTS

Results show that the characteristic AEP waveform in response to consonant-vowel-syllables is on a par with those of non-speech sounds with analogue temporal characteristics. The amplitude of the N1a and N1b component of the auditory evoked potentials significantly correlated with the duration of the VOT in CV and likewise, with the duration of the NOT in non-speech sounds.Furthermore, current density maps indicate overlapping supratemporal networks involved in the perception of both speech and non-speech sounds with a bilateral activation pattern during the N1a time window and leftward asymmetry during the N1b time window. Elaborate regional statistical analysis of the activation over the middle and posterior portion of the supratemporal plane (STP) revealed strong left lateralized responses over the middle STP for both the N1a and N1b component, and a functional leftward asymmetry over the posterior STP for the N1b component.

CONCLUSION

The present data demonstrate overlapping spatio-temporal brain responses during the perception of temporal acoustic cues in both speech and non-speech sounds. Source estimation evidences a preponderant role of the left middle and posterior auditory cortex in speech and non-speech discrimination based on temporal features. Therefore, in congruency with recent fMRI studies, we suggest that similar mechanisms underlie the perception of linguistically different but acoustically equivalent auditory events on the level of basic auditory analysis.

Orthographic and phonological processing in Chinese dyslexic children: An ERP study on sentence reading

An event-related potential (ERP) experiment was conducted to explore the differences between Chinese-speaking dyslexic children and normal school children in orthographic and phonological processing during Chinese sentence reading. Participants were visually presented with sentences, word-by-word and were asked to judge whether the sentences were semantically acceptable. The crucial manipulation was on the sentence-final two-character compound words, which were either correct or incorrect. For the incorrect compounds, the second characters of the base words were replaced by homophonic or orthographically similar characters. It was found that, for the normal controls, the orthographic and phonological mismatches elicited more negative ERP responses, relative to the baseline, over a relatively long time course (including the time windows for P200 and N400) at the central-posterior scalp regions. In contrast, the dyslexic children in general showed no differences between experimental conditions for P200 and N400, although the more detailed time course analyses did reveal some weak effects for the N400 component between experimental conditions. In addition, the mean amplitude of N400 in the homophonic condition was less negative-going for the dyslexics than for the controls. These findings suggest that Chinese dyslexic children have deficits in processing orthographic and phonological information conveyed by characters and, compared with normal children, they rely more on phonological information to access lexical semantics in sentence reading.

Top-down processes during auditory phoneme categorization in dyslexia: A PET study

While persistence of subtle phonological deficits in dyslexic adults is well documented, deficit of categorical perception of phonemes has received little attention so far. We studied learning of phoneme categorization during an activation H(2)O(15) PET experiment in 14 dyslexic adults and 16 normal readers with similar age, handedness and performance IQ. Dyslexic subjects exhibited typical, marked impairments in reading and phoneme awareness tasks. During the PET experiment, subjects performed a discrimination task involving sine wave analogues of speech first presented as pairs of electronic sounds and, after debriefing, as syllables /ba/ and /da/. Discrimination performance and brain activation were compared between the acoustic mode and the speech mode of the task which involved physically identical stimuli; signal changes in the speech mode relative to the acoustic mode revealed the neural counterparts of phonological top-down processes that are engaged after debriefing. Although dyslexic subjects showed good abilities to learn discriminating speech sounds, their performance remained lower than those of normal readers on the discrimination task over the whole experiment. Activation observed in the speech mode in normal readers showed a strongly left-lateralized pattern involving the superior temporal, inferior parietal and inferior lateral frontal cortex. Frontal and parietal subparts of these left-sided regions were significantly more activated in the control group than in the dyslexic group. Activations in the right frontal cortex were larger in the dyslexic group than in the control group for both speech and acoustic modes relative to rest. Dyslexic subjects showed an unexpected large deactivation in the medial occipital cortex for the acoustic mode that may reflect increased effortful attention to auditory stimuli.

Behavioural and event-related potentials evidence for pitch discrimination deficits in dyslexic children: improvement after intensive phonic intervention

Although it is commonly accepted that dyslexic children have auditory phonological deficits, the precise nature of these deficits remains unclear. This study examines potential pitch processing deficit in dyslexic children, and recovery after specific training, by measuring event-related brain potentials (ERPs) and behavioural responses to pitch manipulations within natural speech. In two experimental sessions, separated by 6 weeks of training, 10 dyslexic children, aged 9-12, were compared to reading age-matched controls, using sentences from children's books. The pitch of the sentence's final words was parametrically manipulated (either congruous, weakly or strongly incongruous). While dyslexics followed a training focused on phonological awareness and grapheme-to-phoneme conversion, controls followed a non-auditory training. Before training, controls outperformed dyslexic children in the detection of the strong pitch incongruity. Moreover, while strong pitch incongruities were associated with increased late positivity (P300 component) in controls, no such pattern was found in dyslexics. Most importantly, pitch discrimination performance was significantly improved, and the amplitude of the late positivity to the strong pitch incongruity enhanced, for dyslexics after a relatively brief period of training, so that their pattern of response more closely resemble those of controls.

Abnormalities in central auditory maturation in children with language-based learning problems

OBJECTIVE

To examine maturation of the central auditory pathways in children with language-based learning problems (LP).

METHODS

Cortical auditory evoked potentials (CAEPs) recorded from 26 children with LP were compared to CAEPs recorded from 38 typical children. CAEP responses were recorded in response to a speech sound, /uh/, which was presented in a stimulus train with decreasing inter-stimulus intervals (ISIs) of 2000, 1000, 560, and 360 ms.

RESULTS

We identified three atypical morphological categories of CAEP responses in the LP group. Category 1 responses revealed delayed P1 latencies and absent N1/P2 components. Category 2 responses revealed typical P1 responses, but delayed N1 and P2 responses. Category 3 responses revealed generally low-amplitude CAEP responses. A fourth sub-group of LP children had normal CAEP responses.

CONCLUSIONS

Overall, the majority of children with LP had abnormal CAEP responses. These children fell into distinct categories based on the abnormalities in maturational patterns of their CAEP responses.

SIGNIFICANCE

We describe a rate sensitive stimulation paradigm which may be used to identify and categorize LP children who exhibit abnormal patterns of central auditory maturation.