Effect of time and frequency manipulation on syllable perception in developmental dyslexics

Speech Recognition in Noise by Children with and without Dyslexia: How is it Related to Reading?

PURPOSE

Developmental dyslexia is commonly viewed as a phonological deficit that makes it difficult to decode written language. But children with dyslexia typically exhibit other problems, as well, including poor speech recognition in noise. The purpose of this study was to examine whether the speech-in-noise problems of children with dyslexia are related to their reading problems, and if so, if a common underlying factor might explain both. The specific hypothesis examined was that a spectral processing disorder results in these children receiving smeared signals, which could explain both the diminished sensitivity to phonological structure - leading to reading problems - and the speech recognition in noise difficulties. The alternative hypothesis tested in this study was that children with dyslexia simply have broadly based language deficits.

PARTICIPANTS

Ninety-seven children between the ages of 7 years; 10 months and 12 years; 9 months participated: 46 with dyslexia and 51 without dyslexia.

METHODS

Children were tested on two dependent measures: word reading and recognition in noise with two types of sentence materials: as unprocessed (UP) signals, and as spectrally smeared (SM) signals. Data were collected for four predictor variables: phonological awareness, vocabulary, grammatical knowledge, and digit span.

RESULTS

Children with dyslexia showed deficits on both dependent and all predictor variables. Their scores for speech recognition in noise were poorer than those of children without dyslexia for both the UP and SM signals, but by equivalent amounts across signal conditions indicating that they were not disproportionately hindered by spectral distortion. Correlation analyses on scores from children with dyslexia showed that reading ability and speech-in-noise recognition were only mildly correlated, and each skill was related to different underlying abilities.

CONCLUSIONS

No substantial evidence was found to support the suggestion that the reading and speech recognition in noise problems of children with dyslexia arise from a single factor that could be defined as a spectral processing disorder. The reading and speech recognition in noise deficits of these children appeared to be largely independent.

Perceptual organization of speech signals by children with and without dyslexia

Developmental dyslexia is a condition in which children encounter difficulty learning to read in spite of adequate instruction. Although considerable effort has been expended trying to identify the source of the problem, no single solution has been agreed upon. The current study explored a new hypothesis, that developmental dyslexia may be due to faulty perceptual organization of linguistically relevant sensory input. To test that idea, sentence-length speech signals were processed to create either sine-wave or noise-vocoded analogs. Seventy children between 8 and 11 years of age, with and without dyslexia participated. Children with dyslexia were selected to have phonological awareness deficits, although those without such deficits were retained in the study. The processed sentences were presented for recognition, and measures of reading, phonological awareness, and expressive vocabulary were collected. Results showed that children with dyslexia, regardless of phonological subtype, had poorer recognition scores than children without dyslexia for both kinds of degraded sentences. Older children with dyslexia recognized the sine-wave sentences better than younger children with dyslexia, but no such effect of age was found for the vocoded materials. Recognition scores were used as predictor variables in regression analyses with reading, phonological awareness, and vocabulary measures used as dependent variables. Scores for both sorts of sentence materials were strong predictors of performance on all three dependent measures when all children were included, but only performance for the sine-wave materials explained significant proportions of variance when only children with dyslexia were included. Finally, matching young, typical readers with older children with dyslexia on reading abilities did not mitigate the group difference in recognition of vocoded sentences. Conclusions were that children with dyslexia have difficulty organizing linguistically relevant sensory input, but learn to do so for the structure preserved by sine-wave signals before they do so for other sorts of signal structure. These perceptual organization deficits could account for difficulties acquiring refined linguistic representations, including those of a phonological nature, although ramifications are different across affected children.

The development of language-specific and language-independent talker processing

PURPOSE

In this study, the authors aimed to investigate how differences in language ability relate to differences in processing talker information in the native language and an unfamiliar language by comparing performance for different ages and for groups with impaired language.

METHOD

Three groups of native English listeners with typical language development (TLD; ages 7-9, ages 10-12, adults) and 2 groups with specific language impairment (SLI; ages 7-9, ages 10-12) participated in the study. Listeners heard pairs of words in both English and German (unfamiliar language) and were asked to determine whether the words were produced by the same or different talkers.

RESULTS

In English, talker discrimination improved with age. In German, performance improved with age for the school-age children but was worse for adult listeners. No differences were found between TLD and SLI children.

CONCLUSION

These results show that as listeners' language skills develop, there is a trade-off between more general perceptual abilities useful for processing talker information in any language and those that are relevant to their everyday language experiences and, thus, tied to the phonology. The lack of differences between the children with and without language impairments suggests that general auditory processing may be intact in at least some children with SLI.

Computer-based training with ortho-phonological units in dyslexic children: new investigations

This study aims to show that training using a computer game incorporating an audio-visual phoneme discrimination task with phonological units, presented simultaneously with orthographic units, might improve literacy skills. Two experiments were conducted, one in secondary schools with dyslexic children (Experiment 1) and the other in a speech-therapy clinic with individual case studies (Experiment 2). A classical pre-test, training, post-test design was used. The main findings indicated an improvement in reading scores after short intensive training (10 h) in Experiment 1 and progress in the reading and spelling scores obtained by the dyslexic children (training for 8 h) in Experiment 2. These results are discussed within the frameworks of both the speech-specific deficit theory of dyslexia and the connectionist models of reading development.

A randomized, controlled study of computer-based intervention in middle school struggling readers

The current study was conducted to test the premise that computer-based intervention that targets auditory temporal processing combined with language exercises (Fast ForWord) is effective in remediating children with disorders of language and reading. Sixty-five middle school struggling readers were randomly assigned to one of five groups and over a 12-week-period received one of the following interventions: (1) two phases of intervention with Fast ForWord (FFW, experimental group), (2) two phases of intervention with SuccessMaker (SM, active control group), (3) FFW followed by SM, (4) SM followed by FFW, or (5) no intervention beyond the regular class curriculum (developmental control group). Changes in reading, phonemic awareness, spelling and language skills were assessed via a repeated measures MANOVA. Results indicated significant within-subjects effects (i.e., change for all participants over time), but no between-subject group differences, failing to show that Fast ForWord resulted in any gains over and above those seen in the other groups.

Locus and nature of perceptual phonological deficit in Spanish children with reading disabilities

The aims of this study were (a) to determine whether Spanish children with reading disabilities (RD) show a speech perception deficit and (b) to explore the locus and nature of this perceptive deficit. A group of 29 children with RD, 41 chronological age-matched controls, and 27 reading ability-matched younger controls were tested on tasks of speech perception. The effect of linguistic unit (word vs. syllable) and type of phonetic contrast (voicing, place and manner of articulation) were analyzed in terms of the number of errors and the response time. The results revealed a speech perception deficit in Spanish children with RD that was independent of the type of phonetic contrast and of linguistic unit.

Phonological but not auditory discrimination is impaired in dyslexia

Deficient phonological skills are considered to be a core problem in developmental dyslexia. Children with dyslexia often demonstrate poorer performance than non-impaired readers when categorizing speech-sounds. Using the automatic mismatch response, we show that in contrast to this deficit at the behavioural level, neurophysiological responding in dyslexic children indicates their ability to automatically discriminate syllables. Therefore, the phonological deficit is unlikely to be caused by a temporal deficit or by a noisy functional organization in the respective representational cortex. We obtained measures of reading, spelling and categorical speech-perception from 58 dyslexic children and 21 control children. The children also participated in magnetoencephalographic measurements while being stimulated acoustically with the syllables /ba/ and /da/ in an oddball paradigm. Mismatch field (MMF) amplitudes between standard and deviant stimuli were obtained. Dyslexic children performed more poorly than control children on all test measures. However, the groups did not differ in MMF amplitude or latency. No correlations were found between MMF amplitudes and behavioural performance. These results were obtained with a large sample size and thus speak robustly against a general deficit in auditory discrimination in dyslexia. These results are compatible with the idea that decoding difficulties occur later in the processing stream where access to the phonological lexicon is attempted.

Perception of matching and conflicting audiovisual speech in dyslexic and fluent readers: An fMRI study at 3 T

We presented phonetically matching and conflicting audiovisual vowels to 10 dyslexic and 10 fluent-reading young adults during "clustered volume acquisition" functional magnetic resonance imaging (fMRI) at 3 T. We further assessed co-variation between the dyslexic readers' phonological processing abilities, as indexed by neuropsychological test scores, and BOLD signal change within the visual cortex, auditory cortex, and Broca's area. Both dyslexic and fluent readers showed increased activation during observation of phonetically conflicting compared to matching vowels within the classical motor speech regions (Broca's area and the left premotor cortex), this activation difference being more extensive and bilateral in the dyslexic group. The between-group activation difference in conflicting > matching contrast reached significance in the motor speech regions and in the left inferior parietal lobule, with dyslexic readers exhibiting stronger activation than fluent readers. The dyslexic readers' BOLD signal change co-varied with their phonological processing abilities within the visual cortex and Broca's area, and to a lesser extent within the auditory cortex. We suggest these findings as reflecting dyslexic readers' greater use of motor-articulatory and visual strategies during phonetic processing of audiovisual speech, possibly to compensate for their difficulties in auditory speech perception.

Does successful training of temporal processing of sound and phoneme stimuli improve reading and spelling?

OBJECTIVE

The aim of this study was to measure and train auditory temporal processing in children with dyslexia and to examine whether there was a transfer of improved auditory temporal processing to reading and spelling skills.

METHODS

Computer-based procedures to measure and train temporal processing of sound and phoneme stimuli were developed. Test-scores for a normal control group consisting of 8-year-olds were established. Second graders with dyslexia were included in the training condition and divided into three groups: a control group, a group specifically trained in sound processing, and a third group specifically trained in phoneme processing. After an initial diagnostic procedure, both training groups received specific training every day for 4 weeks. All children, regardless of the group, received the same standard reading training programme designed for children with dyslexia at school. Outcome measures were assessed immediately after training as well as 6 and 12 months later.

RESULTS

Tests for temporal processing of sound and phoneme stimuli proved to be highly reliable. Children with dyslexia (N = 44) showed impaired auditory processing of sound and phoneme stimuli compared to normal controls (N = 51). There was a specific significant improvement in sound, respectively phoneme, processing for the training groups immediately after the end of training. The improvement of phoneme processing remained stable after 6 months and as a trend after 12 months. After 6 and 12 months of training, children of all three groups improved significantly in reading no matter what group. In spelling, the sound training group had a slight advantage after 6 months, which was not stable after 12 months.

CONCLUSIONS

Auditory temporal processing could be trained effectively at the sound and phoneme levels. However, no significant stable transfer of these improved abilities on reading and spelling exceeding the effect of the school-based standard training was demonstrated.

Effects of lengthening the speech signal on auditory word discrimination in kindergartners with SLI

In the present study, it was investigated whether kindergartners with specific language impairment (SLI) and normal language achieving (NLA) kindergartners can benefit from slowing down the entire speech signal or part of the speech signal in a synthetic speech discrimination task. Subjects were 19 kindergartners with SLI and 24 NLA controls. Results showed both types of speech manipulation to positively influence word discrimination for the entire group of children. Further analysis made clear that the effects were due to the improvement of the scores of the lowest 25% scorers (8 SLI, 3 NLA).

LEARNING OUTCOMES

As a result of this activity, the reader will be able to: (1) give an overview on the effects of speech manipulation on discrimination abilities of children with SLI, (2) be able to look with more nuance at the reported effects of the FFW software program.

Specific reading disability (dyslexia): what have we learned in the past four decades?

We summarize some of the most important findings from research evaluating the hypothesized causes of specific reading disability ('dyslexia') over the past four decades. After outlining components of reading ability, we discuss manifest causes of reading difficulties, in terms of deficiencies in component reading skills that might lead to such difficulties. The evidence suggests that inadequate facility in word identification due, in most cases, to more basic deficits in alphabetic coding is the basic cause of difficulties in learning to read. We next discuss hypothesized deficiencies in reading-related cognitive abilities as underlying causes of deficiencies in component reading skills. The evidence in these areas suggests that, in most cases, phonological skills deficiencies associated with phonological coding deficits are the probable causes of the disorder rather than visual, semantic, or syntactic deficits, although reading difficulties in some children may be associated with general language deficits. Hypothesized deficits in general learning abilities (e.g., attention, association learning, cross-modal transfer etc.) and low-level sensory deficits have weak validity as causal factors in specific reading disability. These inferences are, by and large, supported by research evaluating the biological foundations of dyslexia. Finally, evidence is presented in support of the idea that many poor readers are impaired because of inadequate instruction or other experiential factors. This does not mean that biological factors are not relevant, because the brain and environment interact to produce the neural networks that support reading acquisition. We conclude with a discussion of the clinical implications of the research findings, focusing on the need for enhanced instruction.

Impaired processing of brief, rapidly presented auditory cues in infants with a family history of autoimmune disorder

Studies have shown that individuals with language disorders, such as developmental dyslexia and specific language impairment, exhibit impairments in the processing of brief, successive, or rapidly changing auditory information. It is also the case that a higher rate of autoimmune disorders have been identified in those with language-based learning disorders and, conversely, that individuals with autoimmune disorders show a higher incidence of language-related disorders. The rapid auditory processing (RAP) deficits described for older individuals with language impairments may also be used as a behavioral marker to identify infants at higher risk for language delays. Thus, we were interested in examining RAP abilities in a subset of infants with a positive family history of autoimmune disorders. Eleven infants from our ongoing prospective longitudinal studies were identified based on parental response to a question about the presence of a family history of autoimmune disease and compared to 11 matched controls. The RAP threshold of each infant was assessed at 6 and 9 months of age using a conditioned head-turn procedure (using tone pairs with brief interstimulus intervals) and an auditory-visual habituation-recognition memory task using computer-generated consonant-vowel syllables (/ba/ vs. /da/). A visual habituation-recognition memory task that did not require processing of brief temporal cues was also administered. Group differences emerged on the infant RAP tasks, and on language outcome measures at 12 and 16 months of age. Infants from families with a history of autoimmune disorder had significantly higher (i.e., poorer) RAP thresholds and lower language scores than did control infants, whereas visual discrimination scores did not differ between family history infants and controls. Moreover, when brief auditory cues were necessary for the discrimination of /ba/ vs. /da/, infants with a family history of autoimmune disorder performed significantly more poorly than did controls. These findings lend support to the hypothesis that a similar mechanism, perhaps a neural-immune interaction, may underlie the observed co-occurrence of autoimmune disorders and learning impairments.

[Reliability, trainability and stability of auditory discrimination performance in 2 computer-assisted assessment and training methods]

OBJECTIVES

The present study focuses on the possibilities and effects of training dyslexic children in tone and phoneme discrimination tasks.

METHODS

A computer program was developed to train dyslexic children to discriminate between tone and speech stimuli. The correlation between auditory discrimination and reading and orthography performance was then tested in a preliminary study of n = 63 children. In a prospective study 44 children were assigned to one of three paralyzed groups: tone training, phoneme training or a control group. Upon completion of the initial diagnostics for all groups, the two training groups received four weeks of discrimination training, after which all three groups were immediately re-tested for the first time. Parallel thereto all children underwent specific training in reading and orthography at their school. Six months later all were re-tested a second time.

RESULTS

Both test methods showed a high reliability (rn = .94; .95). Significant correlations between auditory discrimination and reading and orthography performance were confirmed. Auditory discrimination was significantly trainable. Specific training effects, as well as independent developmental effects were found. While the training effects of phoneme discrimination were stable over six months, those of tone discrimination were not.

CONCLUSION

The central auditory discrimination between tone and phoneme stimuli can be trained successfully in dyslexic children and might also affect their reading and orthography performance.

Infant discrimination of rapid auditory cues predicts later language impairment

The etiology and mechanisms of specific language impairment (SLI) in children are unknown. Differences in basic auditory processing abilities have been suggested to underlie their language deficits. Studies suggest that the neuropathology, such as atypical patterns of cerebral lateralization and cortical cellular anomalies, implicated in such impairments likely occur early in life. Such anomalies may play a part in the rapid processing deficits seen in this disorder. However, prospective, longitudinal studies in infant populations that are critical to examining these hypotheses have not been done. In the study described, performance on brief, rapidly-presented, successive auditory processing and perceptual-cognitive tasks were assessed in two groups of infants: normal control infants with no family history of language disorders and infants from families with a positive family history for language impairment. Initial assessments were obtained when infants were 6-9 months of age (M=7.5 months) and the sample was then followed through age 36 months. At the first visit, infants' processing of rapid auditory cues as well as global processing speed and memory were assessed. Significant differences in mean thresholds were seen in infants born into families with a history of SLI as compared with controls. Examination of relations between infant processing abilities and emerging language through 24 months-of-age revealed that threshold for rapid auditory processing at 7.5 months was the single best predictor of language outcome. At age 3, rapid auditory processing threshold and being male, together predicted 39-41% of the variance in language outcome. Thus, early deficits in rapid auditory processing abilities both precede and predict subsequent language delays. These findings support an essential role for basic nonlinguistic, central auditory processes, particularly rapid spectrotemporal processing, in early language development. Further, these findings provide a temporal diagnostic window during which future language impairments may be addressed.

Intelligibility of modified speech for young listeners with normal and impaired hearing

Exposure to modified speech has been shown to benefit children with language-learning impairments with respect to their language skills (M. M. Merzenich et al., 1998; P. Tallal et al., 1996). In the study by Tallal and colleagues, the speech modification consisted of both slowing down and amplifying fast, transitional elements of speech. In this study, we examined whether the benefits of modified speech could be extended to provide intelligibility improvements for children with severe-to-profound hearing impairment who wear sensory aids. In addition, the separate effects on intelligibility of slowing down and amplifying speech were evaluated. Two groups of listeners were employed: 8 severe-to-profoundly hearing-impaired children and 5 children with normal hearing. Four speech-processing conditions were tested: (1) natural, unprocessed speech; (2) envelope-amplified speech; (3) slowed speech; and (4) both slowed and envelope-amplified speech. For each condition, three types of speech materials were used: words in sentences, isolated words, and syllable contrasts. To degrade the performance of the normal-hearing children, all testing was completed with a noise background. Results from the hearing-impaired children showed that all varieties of modified speech yielded either equivalent or poorer intelligibility than unprocessed speech. For words in sentences and isolated words, the slowing-down of speech had no effect on intelligibility scores whereas envelope amplification, both alone and combined with slowing-down, yielded significantly lower scores. Intelligibility results from normal-hearing children listening in noise were somewhat similar to those from hearing-impaired children. For isolated words, the slowing-down of speech had no effect on intelligibility whereas envelope amplification degraded intelligibility. For both subject groups, speech processing had no statistically significant effect on syllable discrimination. In summary, without extensive exposure to the speech processing conditions, children with impaired hearing and children with normal hearing listening in noise received no intelligibility advantage from either slowed speech or envelope-amplified speech.

Auditory temporal processing performance of young adults with reading disorders

The present study investigated the temporal processing abilities of college students with diagnosed reading disorders. A behavioral test battery was used that involved discrimination of the pattern of presentation of tone triads in which individual components differed in either frequency or duration. An additional test involving measurement of frequency difference limens for long- and short-duration tones was also administered. The college students with reading disorders exhibited significantly higher error rates in discriminating duration patterns than the normal reading group. No group differences were found for the frequency pattern discrimination task. Both groups exhibited larger frequency difference limens with the shorter 20- and 50-ms tones than with the 200-ms tones. Significant correlations were found between reading ability measures and temporal processing abilities, specifically in word recognition and duration pattern processing, suggesting a relationship between lower level auditory temporal processing skills and decoding efficiency.

Temporal processing and phonological impairment in dyslexia: effect of phoneme lengthening on order judgment of two consonants

The evidence of supporting phonological deficit as a cause of developmental dyslexia has been accumulating rapidly over the past 2 decades, yet the exact mechanisms underlying this deficit remain controversial. Some authors assume that a temporal processing deficit is the source of the phonological disorder observed in dyslexic children. Others maintain that the phonological deficit in dyslexia is basically linguistic, not acoustic, in nature. Three experiments were conducted and tested the impact of the temporal alteration and the impact of complex syllabic structure on consonant order judgments. Thirteen phonological dyslexics (age 10-13) and 10 controls matched for chronologial age were compared on a Temporal Order Judgment (TOJ) task using the succession of two consonants (/p/ /s/) within a cluster. In order to test the possible relevance of the temporal deficit hypothesis, the task also included two additional conditions where either the two stimuli were artificially slowed or two phonological structures were opposed (CCV and CVCV). As expected, the TOJ performance was significantly poorer in dyslexics than in controls. Moreover, in the "slowed speech" condition dyslexics' performance improved to reach the normal controls' level, whereas manipulating the phonological structure complexity provided no significant improvement. Finally dyslexics' performances, especially on the slowed condition, were found correlated with several tests of phonological processing. These results lend support to the general temporal deficit theory of dyslexia.

Speech comprehension is correlated with temporal response patterns recorded from auditory cortex

Speech comprehension depends on the integrity of both the spectral content and temporal envelope of the speech signal. Although neural processing underlying spectral analysis has been intensively studied, less is known about the processing of temporal information. Most of speech information conveyed by the temporal envelope is confined to frequencies below 16 Hz, frequencies that roughly match spontaneous and evoked modulation rates of primary auditory cortex neurons. To test the importance of cortical modulation rates for speech processing, we manipulated the frequency of the temporal envelope of speech sentences and tested the effect on both speech comprehension and cortical activity. Magnetoencephalographic signals from the auditory cortices of human subjects were recorded while they were performing a speech comprehension task. The test sentences used in this task were compressed in time. Speech comprehension was degraded when sentence stimuli were presented in more rapid (more compressed) forms. We found that the average comprehension level, at each compression, correlated with (i) the similarity between the frequencies of the temporal envelopes of the stimulus and the subject's cortical activity ("stimulus-cortex frequency-matching") and (ii) the phase-locking (PL) between the two temporal envelopes ("stimulus-cortex PL"). Of these two correlates, PL was significantly more indicative for single-trial success. Our results suggest that the match between the speech rate and the a priori modulation capacities of the auditory cortex is a prerequisite for comprehension. However, this is not sufficient: stimulus-cortex PL should be achieved during actual sentence presentation.

Temporal resolution of auditory perception in relation to perception, memory, and language skills in typical children

This study examined temporal resolution of auditory perception (TRAP) in relation to speech perception and phonological working memory in one experiment and in relation to measures of rapid naming, understanding of grammatical contrasts, and phonological awareness in a second experiment. In the TRAP test, 6- to 9-year-old children discriminated four pairs of two sine tones, 878 Hz and 1350 Hz, presented in blocks with stepwise decreasing interstimulus intervals from 256 ms to 8 ms. In Experiment 1, weak but significant correlations between TRAP and speech perception and phonological working memory were found, as well as a significantly lower TRAP performance by girls. Experiment 2 indicated a significant relation between TRAP and the phonological awareness task. The results give qualified support to the notion of a weak relationship between TRAP and speech perception and language skills among typical children. However, the gender differences in TRAP performance, the limited variance explained by the regression models, and the finding that only one of the language parameters correlated with TRAP do not support the notion of a causal relationship between language skills and TRAP. The possibility that TRAP is connected to general neurological maturation rather than specifically to language abilities is discussed.

Use of temporal envelope cues by children with developmental dyslexia

This study evaluates the ability to process auditory temporal-envelope cues in a group of 6 children with dyslexia (mean age: 10;10 years;months). To address this issue, we measured (a) temporal modulation transfer functions (TMTFs), that is, the detection thresholds of sinusoidal amplitude modulation (SAM) applied to a white noise carrier, as a function of modulation frequency, fm (fm was 4, 16, 64, 256, and 1,024 Hz) and (b) identification performance for vowel-consonant-vowel (VCV) stimuli over 5 sessions. VCV stimuli were either unprocessed or digitally processed to remove the original spectral information, resulting in a time-varying speech envelope amplitude modulating a noise carrier. The same tests were conducted in 6 normal control children (mean age: 11;6 years;months) and 6 normal control adults (mean age: 24;8 years;months). SAM thresholds were similar in normal children and adults. For both normal groups, TMTFs were low pass in shape and showed low between-listener variability. TMTFs measured in children with dyslexia showed higher between-listener variability: TMTFs were band pass in 2 children, flat in 1 child, and low pass in the 3 others. Overall, SAM thresholds were higher in children with dyslexia than in normal children at fm = 4 and 1,024 Hz. Unprocessed-speech identification performance was nearly perfect in normal children and adults, and impaired in children with dyslexia. "Speech-envelope noise" identification performance was poorer in normal children and children with dyslexia than in normal adults. Performance improved across sessions in normal children and adults, but remained constant in children with dyslexia. Compared to normal children, children with dyslexia showed poorer reception of voicing, manner, and place of articulation for unprocessed speech and poorer reception of voicing for "speech-envelope noise." Taken together, these results support the hypothesis that some children with dyslexia may show abnormal auditory temporal-envelope processing. Such a deficit, in turn, may explain the difficulties of children with dyslexia with speech perception.

Phonological and visuo-spatial working memory alterations in dyslexic children

BACKGROUND

Working memory allows the retention of a limited amount of information for a brief period of time and the manipulation of that information. This study was undertaken to compare possible differences in working memory between dyslexic and control children.

METHODS

To test the executive central process that controls attention, subjects were requested to assemble a 100-piece puzzle. To test the phonological loop, subjects were requested to repeat orally a 10-item list with the following characteristics: digits spanning two numbers; phonologically similar words, and unfamiliar pseudowords. The visuo-spatial sketchpad was tested by means of assembling a 25-piece puzzle.

RESULTS

Forty dyslexic and and forty control children were studied. Dyslexic children recall a lesser number of similar words in the phonological loop and spend a longer time in puzzle assembly in the visuo-spatial sketchpad. No statistical difference in the central executive process was found.

CONCLUSIONS

Present results suggest the importance of visuo-spatial and phonological loop alterations in dyslexic children that may result in difficulties with similar words and spatial information.

Speech perception deficits in poor readers: a reply to Denenberg's critique

We reply to Denenberg's (1999) recent critique of our work (Mody, Studdert-Kennedy, & Brady, 1997). Denenberg mounted two main lines of criticism, one concerning characteristics of the population sampled for the experimental group, and the other a statistical critique, concerning (a) violation of parametric assumptions for use of the F distribution and (b) our supposed acceptance of the null hypothesis of no differences between experimental and control groups. We show that the first criticism stemmed from a misunderstanding of the experimental hypothesis and that the second can be answered by both parametric and nonparametric comparisons across conditions within the experimental group, without reference to the control group. Thus, our original conclusion stands: The difficulty with rapid /ba/-/da/ discrimination that some children with reading impairment may experience does not stem from difficulty in discriminating the rapid spectral transitions at stop-vowel syllable onsets.

Do temporal processing deficits cause phonological processing problems?

This study tested the hypothesis that temporal processing deficits underlie phonological processing problems. The subjects were children aged 8 to 10 years (N = 110) who were separated into 2 groups on the basis of whether their reading scores were normal or poor. As predicted by many earlier studies, children with poor reading scores demonstrate poor abilities on tests of phonological awareness, as well as on 2 other language tasks that depend on phonological processing. Two specific tests of the temporal processing hypothesis were conducted. Children in both groups were tested (a) on their abilities to recall sequences of nonspeech tones presented at various rates and (b) on their abilities to make phonetic decisions using brief and transitional properties of the speech signal, especially formant transitions (the purported "trouble spot" in the speech signal for children with phonological processing problems). The children with poor phonological processing abilities showed no special difficulty recalling rapidly presented nonspeech stimuli, and, in their phonetic decisions, they were able to use brief and transitional signal properties, including formant transitions, at least as well as other children. Therefore, no evidence was found to support the hypothesis that temporal processing deficits cause phonological processing problems.

Psychophysical sensitivity and physiological response to amplitude modulation in adult dyslexic listeners

This study reports two experiments conducted to assess the sensitivity of dyslexic listeners to amplitude modulation (AM) of acoustic stimuli. The smallest detectable depth of AM of white noise was measured as a function of modulation frequency. Dyslexic listeners had significantly higher thresholds of AM depth than did matched control listeners. We also recorded the scalp potential evoked by AM of white noise (the amplitude modulation following response, AMFR). Dyslexic listeners had significantly smaller AMFRs than did matched control listeners. The reduced AMFR is consistent with reduced sensitivity to AM, and there was a strong association between these psychophysical and physiological measures. This deficit in AM sensitivity may result in impaired perception of the AM present in speech.

Central auditory processing disorder in school-aged children: a critical review

The rationale to evaluate for central auditory processing disorder (CAPD) in school-aged children is based on the assumption that an auditory-specific perceptual deficit underlies many learning problems including specific reading and language disabilities. A fundamental issue in this area is whether convincing empirical evidence exists to validate this proposition. Herein, we consider the issue of modality specificity by examining the extent to which reading, language, and attention disorders in school-aged children involve perceptual dysfunctions limited to a single sensory modality. Difficulty in validating CAPD as a diagnostic label is due in large part to use of the unimodal inclusive framework, which has biased the diagnosis to favor sensitivity of test results over documenting the specificity of the deficit. Indeed, empirical research documenting modality-specific auditory-perceptual dysfunction in this population is scarce. Therefore, the existing literature on this topic has not clarified the "true" nature of the problem, and has left many questions about this disorder unanswered. It is argued that demonstrating modality specificity is one way to rule out supramodal disorders as explanations for observed dysfunction. Multimodal perceptual testing is one logical approach to help clarify this area of investigation.