Rate of acoustic change may underlie hemispheric specialization for speech perception.

Phonemically similar syllables, differing only by temporal acoustic cues, were presented dichotically to investigate temporal processing mechanisms in hemispheric specialization for speech. Reducing the rate of acoustic change within syllables while keeping their phonemic characteristics constant significantly decreased the characteristic asymmetry in processing speech.

Temporal processing deficits of language-learning impaired children ameliorated by training.

Children with language-based learning impairments (LLIs) have major deficits in their recognition of some rapidly successive phonetic elements and nonspeech sound stimuli. In the current study, LLI children were engaged in adaptive training exercises mounted as computer "games" designed to drive improvements in their "temporal processing" skills. With 8 to 16 hours of training during a 20-day period, LLI children improved markedly in their abilities to recognize brief and fast sequences of nonspeech and speech stimuli.

Language comprehension in language-learning impaired children improved with acoustically modified speech.

A speech processing algorithm was developed to create more salient versions of the rapidly changing elements in the acoustic waveform of speech that have been shown to be deficiently processed by language-learning impaired (LLI) children. LLI children received extensive daily training, over a 4-week period, with listening exercises in which all speech was translated into this synthetic form. They also received daily training with computer "games" designed to adaptively drive improvements in temporal processing thresholds. Significant improvements in speech discrimination and language comprehension abilities were demonstrated in two independent groups of LLI children.

Neural correlates of rapid auditory processing are disrupted in children with developmental dyslexia and ameliorated with training: an fMRI study.

PURPOSE: Developmental dyslexia, characterized by unexpected difficulty in reading, may involve a fundamental deficit in processing rapid acoustic stimuli. Using functional magnetic resonance imaging (fMRI) we previously reported that adults with developmental dyslexia have a disruption in neural response to rapid acoustic stimuli in left prefrontal cortex. Here we examined the neural correlates of rapid auditory processing in children. METHODS: Whole-brain fMRI was performed on twenty-two children with developmental dyslexia and twenty-three typical-reading children while they listened to nonlinguistic acoustic stimuli, with either rapid or slow transitions, designed to mimic the spectro-temporal structure of consonant-vowel-consonant speech syllables. RESULTS: Typical-reading children showed activation for rapid compared to slow transitions in left prefrontal cortex. Children with developmental dyslexia did not show any differential response in these regions to rapid versus slow transitions. After eight weeks of remediation focused primarily on rapid auditory processing, phonological and linguistic training the children with developmental dyslexia showed significant improvements in language and reading skills, and exhibited activation for rapid relative to slow transitions in left prefrontal cortex. CONCLUSION: The presence of a disruption in the neural response to rapid stimuli in children with developmental dyslexia prior to remediation, coupled with significant improvement in language and reading scores and increased brain activation after remediation, gives further support to the importance of rapid auditory processing in reading development and disorders.

Speech and other central auditory processes: insights from cognitive neuroscience.

Recent advances in cognitive neuroscience, particularly studies utilizing functional neural imaging and animal models, are providing unique insights into the neural substrates of speech and other central auditory processes. In particular, the acoustic-phonetic aspects of speech appear to provide an important organizing principle for linking systems neuroscience research to cognitive and linguistic theories.

Neural correlates of rapid spectrotemporal processing in musicians and nonmusicians.

Our results suggest that musical training alters the functional anatomy of rapid spectrotemporal processing, resulting in improved behavioral performance along with a more efficient functional network primarily involving traditional language regions. This finding may have important implications for improving language/reading skills, especially in children struggling with dyslexia.

Cerebral structure on magnetic resonance imaging in language- and learning-impaired children.

Using magnetic resonance imaging 20 language- and learning-impaired children were compared with 12 normal control subjects. Gross brain structure was remarkably normal in the language- and learning-impaired group. Semiautomated morphometry was used to measure hemispheric volumes and cerebral asymmetries in six cerebral regions. The volume of the left posterior perisylvian region was significantly reduced in language- and learning-impaired children. Asymmetries in inferoanterior and superoposterior cerebral regions were also significantly different in this group. Results of descriptive group comparisons of estimated volumes of other cerebral gray-matter structures raise the possibility that some language- and learning-impaired children may have additional volume reductions in cortical and subcortical structures. The results suggest that hemispheric specialization of function may be anomalous in this population.

Cerebral brain metabolism in adult dyslexic subjects assessed with positron emission tomography during performance of an auditory task.

Ten dyslexic adults (aged 33.5 +/- 7.3 years, nine men, one woman) and 10 age-, sex- and handedness-matched control subjects (aged 33.6 +/- 5.8 years) performed an auditory syllable discrimination task during 18-fluoro-2-deoxyglucose uptake, and then underwent positron emission tomographic scans. A second normal control group performed an analogous visual discrimination task. Dyslexic subjects experienced greater difficulty and made significantly more errors in performing the auditory task. There were no differences in brain metabolic rates in lateral cortical areas (frontal, parietal, temporal, and occipital lobes). A significant difference emerged in the medial temporal lobe, with dyslexic subjects having significantly higher absolute and relative brain metabolism along an anterior-posterior gradient than normal adults. These data support the hypothesis of altered cerebral processing of auditory stimuli in patients with dyslexia.

Unexpected sex-ratios in families of language/learning-impaired children.

There is a well-documented propensity of males affected with developmental language/learning impairment. Results from this study demonstrate, unexpectedly, that this sex-ratio difference of males to females with developmental language/learning disorders was found to occur significantly only in families with a language/learning-impaired mother. In addition, a remarkably aberrant offspring sex-ratio was found in families of language/learning-impaired children who had an affected mother, but not father. Mothers who were developmentally language/learning-impaired had three times as many sons as daughters, and five times as many language/learning-impaired sons as daughters. Genetic and hormonal influences that might affect both sex-ratio and neuroanatomical development and disorders are discussed.

The relationship between auditory temporal analysis and receptive language development: evidence from studies of developmental language disorder.

The relationship between sensory, perceptual and motor abilities and receptive language abilities was studied in developmental dysphasic children. The tests administered included experimental auditory, visual and cross-modal perceptual tests. In addition, a battery of neurodevelopmental "soft sign" sensory, perceptual and motor tests were also given. Demographic and case history data were collected. Receptive language was derived based upon a battery of standardized language tests. Multivariate analyses were employed to examine the relationship between receptive language and sensory, perceptual and motor abilities. Results demonstrated that auditory perceptual variables, specifically those requiring rapid temporal analysis, were most highly correlated with the degree of receptive language deficit of the dysphasic children.

Verbal learning and memory in language impaired children.

The present study investigated patterns of verbal learning and memory in Language Impaired (LI) and normal children, using the California Verbal Learning Test--Children's Version. The LI children showed a normal immediate memory span; however, they were impaired in the total number of correct responses that they generated across repeated trials. They reported significantly more perseverations, but not intrusions, relative to the controls. The LI children were not impaired on a delayed free recall task, but they were significantly impaired relative to the controls on semantically cued recall. The implications of these findings for future research and for remediation are discussed.

Hormonal influences in developmental learning disabilities.

Developmental language and learning disabilities in children can take many different forms and can result from a variety of causes. Research to date has focused primarily on specific disabilities in learning, which are characterized by a significant delay or disorder in one aspect of learning against a background of otherwise normal development. Learning disabilities affecting language and/or reading acquisition (developmental dysphasia and dyslexia) have been studied most thoroughly. Verbal learning disabilities occur more frequently in boys than in girls, and there is a higher than expected incidence of left-handedness among affected children. Although there are many reasons why a child may have delayed or disordered language development, differential diagnosis of specific developmental language or reading disorders calls for ruling out mental retardation, peripheral auditory or visual dysfunction, autism, frank neurological impairments such as hemiplegia or seizure disorder, and severe social deprivation or lack of educational opportunity. The typical profile of a developmentally dysphasic or dyslexic child is one who shows a marked discrepancy between nonverbal (performance) IQ and verbal IQ, with a history of delayed or disordered speech, language and/or reading development. Such a child usually performs quite normally on visual spatial tasks, while demonstrating severe deficits in tasks of auditory temporal processing, motor sequencing, phonological processing and memory, language, reading and spelling. This characteristic neuropsychological profile may suggest left hemisphere dysfunction or a failure to develop normal cerebral lateralization. The etiology of these developmental learning disorders is unknown, but there is evidence of familial aggregation, indicating a potential genetic basis. Although these children respond to remediation, longitudinal studies have shown that the symptoms often persist into adulthood (see Tallal, 1988, for a more detailed discussion).

Effects of sex and MK-801 on auditory-processing deficits associated with developmental microgyric lesions in rats.

Neonatally induced microgyric lesions produce defects in rapid auditory processing in adult male rats. Given that females across species are less susceptible to the deleterious effects of neural injury and that treatment with neuroprotective agents at the time of injury can reduce neural damage, the authors tested the effects of sex and neuroprotectant exposure on the behavioral consequences of microgyric lesions in rats. Results showed that sham but not microgyric males were able to perform the task at the fastest rate of stimulus presentation. Microgyric females, in contrast, discriminated at all stimulus conditions and did not differ from female shams. Microgyric males treated with MK-801 had reduced cortical damage and performed the discrimination at the fastest condition. Results suggest that females are less susceptible to the behavioral effects of neocortical microgyria and that MK-801 may ameliorate the behavioral consequences of these lesions in male rats.

Functional lateralization for auditory temporal processing in male and female rats.

In 3 studies adult male rats showed significantly better discrimination of tone sequences with the right ear than with the left ear. This result parallels similar findings of left-hemisphere specialization for auditory temporal processing in humans and nonhuman primates. Furthermore, because clinical evidence supports a link between specialization of the left hemisphere for auditory temporal processing and for speech processing, these results may reflect evolutionary precursors to left-hemisphere language specialization. Because male rats showed a stronger ear advantage than female rats, the findings may relate to evidence of a stronger right ear advantage in men than in women. Finally, results suggest that neonatal handling enhances lateralization for auditory temporal processing in both sexes. Combined results implicate neuroendocrine mechanisms as important factors in the development of lateralization for auditory temporal processing.

Disrupted neural responses to phonological and orthographic processing in dyslexic children: an fMRI study.

Developmental dyslexia, characterized by difficulty in reading, has been associated with phonological and orthographic processing deficits. fMRI was performed on dyslexic and normal-reading children (8-12 years old) during phonological and orthographic tasks of rhyming and matching visually presented letter pairs. During letter rhyming, both normal and dyslexic reading children had activity in left frontal brain regions, whereas only normal-reading children had activity in left temporo-parietal cortex. During letter matching, normal-reading children showed activity throughout extrastriate cortex, especially in occipito-parietal regions, whereas dyslexic children had little activity in extrastriate cortex during this task. These results indicate dyslexia may be characterized in childhood by disruptions in the neural bases of both phonological and orthographic processes important for reading.

Language, learning, and behavioral disturbances in childhood: a longitudinal perspective.

OBJECTIVE: Investigate longitudinally the course of development of preschool learning impaired (LI) children to better understand the interaction between neurodevelopmental delay, behavioral/emotional disorders, and language development and disorders. METHOD: Relationships between developmental language disorders and emotional problems were investigated in 99 8-year-old specifically language impaired and control children originally assessed at age 4 years using the Achenbach Child Behavior Checklist and the Conners' Parents Questionnaire. RESULTS: LI children received higher behavior problem scores and were more likely to score in the clinical range than were control children. Neither degree of early language impairment nor amount of language improvement predicted 8-year behavioral/emotional status. LI children with the largest drop in IQ between ages 4 and 8 received the highest behavior problem scores. No significant comorbid relationship was seen between LI and attention-deficit hyperactivity disorder. CONCLUSIONS: The enhanced incidence of behavior problems reported heretofore may be related more to lower IQ than to linguistic deficit per se. Care must be taken to differentiate the symptoms of neurodevelopmental delay and emotional disturbance, however, preschool children with scores in the clinical range on such measures should be referred for additional evaluation.

Impaired two-tone processing at rapid rates in male rats with induced microgyria.

We previously reported that adult male rats with bilateral induced microgyria exhibit deficits in rapid auditory processing, which appear similar to auditory processing deficits seen in individuals with developmental language disabilities. The current study was designed to further elaborate that finding using an improved paradigm in which stimulus duration was uncoupled from testing experience and learning effects. Specifically, two-tone stimuli with durations of 540, 390, 332 and 249 ms were all presented within a single test session in a modified operant conditioning paradigm. Subjects were tested over a period of 12 days using this variable-stimulus format. Results confirmed microgyric male rats were impaired only in processing two-tone stimuli presented at rapid rates (i.e., 249 ms duration). Thus the current results support the previously observed link between focal malformations and deficits in rapid auditory processing.

Perceptual and linguistic factors in the language impairment of developmental dysphasics: an experimental investigation with the token test.

Twelve developmental dysphasics and twelve control children were tested on De Renzi and Vignolo's Token Test. The performance of the dysphasics, though significantly poorer than that of the controls on Parts 2-5 of the test, seemed to follow a similar pattern. Both groups were errorless on the initial parts of the test. As the demand on auditory retention increased on subsequent parts of the test, the performance of both groups progressively deteriorated. However, the addition of grammatical complexity on Part 5, rather than causing even further deterioration in performance, actually served to improve the performance of both groups, though not significantly. Although the pattern of errors made by the two groups was similar, the quantity of errors made by the dysphasics, as compared to the normal control children, demonstrated the magnitude of the dysphasic children's receptive language impairment. Analysis of errors indicated that dysphasic children have greater difficulty with auditory retention and verbal memory than they do with the grammatical or structural complexity of language. It is suggested that the observed gross language impairment of developmentally dysphasic children does not result, at least primarily, from a specific inability to analyze the linguistic components of language. Rather, the language impairment of these children appears to reflect their primary inability to analyze the rapid stream of acoustic information which characterizes speech and is essential to normal speech perception and language development.

Attentional capabilities of reading-impaired children during dichotic presentation of phonetic and complex nonphonetic sounds.

Reading-impaired boys, who were deficient in nonverbal auditory processing skills, were tested on their ability to identify a single speech sound (CV) when presented in dichotic competition with a nontarget CV or complex nonspeech sound (bleat). Sixteen reading-impaired boys aged 9 to 14 and 16 age-matched controls were presented with 30 CV-CV pairs and 30 CV-Bleat pairs. No difference was found between the two groups in their ability to identify the target CV, regardless of whether the competing stimulus was phonetic or nonphonetic. It was concluded that reading-impaired children of the type studied here are characterized more by an attentional capacity limitation than by an inability to focus attention or by a specific inability to process phonetic information.