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

Speed of processing of the visual-orthographic and auditory-phonological systems in adult dyslexics: the contribution of "asynchrony" to word recognition deficits

This study investigated whether "asynchrony" in speed of processing (SOP) between the visual-orthographic and auditory-phonological modalities contributes to word recognition deficits among adult dyslexics. Male university students with a history of diagnosed dyslexia were compared to age-matched normal readers on a variety of experimental measures while event-related potentials and reaction time data were collected. Measures were designed to evaluate auditory and visual processing for non-linguistic (tones and shapes) and linguistic (phonemes and graphemes) low-level stimuli as well as higher-level orthographic and phonological processing (in a lexical decision task). Data indicated that adult dyslexic readers had significantly slower reaction times and longer P300 latencies than control readers in most of the experimental tasks and delayed P200 latencies for the lexical decision task. Moreover, adult dyslexics revealed a systematic SOP gap in P300 latency between the auditory/phonological and visual/orthographic processing measures. Our data support and extend previous work that found SOP asynchrony to be an underlying factor of childhood dyslexia. The present data suggests, however, that among adult dyslexics the between modalities asynchrony occurs at later processing stages than in children.

Computer-based sorting-to-matching in identity matching for young children with developmental disabilities

We evaluated a computer-based sorting-to-matching procedure to teach matching-to-sample skills to seven young children with developmental disabilities who had failed to demonstrate identity matching-to-sample under the typical training procedure (such as observing a sample then selecting a comparison stimulus). In the sorting-to-matching procedure, rather than clicking on a comparison stimulus, the children moved the sample stimulus under the identical comparison stimulus. For all the children, identity matching-to-sample accuracy rapidly increased when the sorting-to-matching procedure was introduced, while it remained at chance levels in the typical training procedure. One of seven children showed collateral gains in accuracy with the typical training procedure after the exposure to the sorting-to-matching procedure.

Word reading and reading-related skills in adolescents with Williams syndrome

BACKGROUND

Individuals with Williams syndrome have good spontaneous language despite low levels of intelligence. This study explores the relationship between intelligence, word decoding and reading-related skills in 20 individuals with Williams syndrome.

METHODS

In addition to the KBIT, the participants were administered standardized measures of reading, vocabulary, rapid naming, phonological skills and an experimental measure of rhyme judgement.

RESULTS

There was wide variability in the reading achievement among the individuals with WS. While some participants were unable to recognize letters of the alphabet, others scored within the normal range of tests of single word reading and decoding. Reading scores were correlated with intelligence as measured on KBIT matrices but not with the vocabulary measures. Reading also correlated with phonological awareness tasks yet, surprisingly, not with rapid naming.

CONCLUSION

It is suggested that in individuals with retardation, intelligence rather than language and language-related skills predict achievements in word reading.

Targeting the CREB pathway for memory enhancers

Today, the clinical notion of 'memory disorder' is largely synonymous with 'Alzheimer's disease.' Only 50% of all dementias are of the Alzheimer's type though, and dementias represent only the more severe of all learning/memory disorders that derive from heredity, disease, injury or age. Perhaps as many as 30 million Americans suffer some type of clinically recognized memory disorder. To date, therapeutic drugs of only one class have been approved for the treatment of Alzheimer's disease. Fortunately, basic research during the past 25 years has begun to define a 'chemistry of brain plasticity,' which is suggesting new gene targets for the discovery of memory enhancers.

Neural plasticity following auditory training in children with learning problems

OBJECTIVE

This study examined the plasticity of the central auditory pathway and accompanying cognitive changes in children with learning problems.

METHODS

Children diagnosed with a learning disability and/or attention deficit disorder worked with commercial auditory processing training software for 8 weeks; control groups consisted of normal-learning and learning-impaired children who did not participate in any remedial programs. Auditory brainstem function was evaluated in response to click and speech stimuli in quiet; cortical responses to speech stimuli were obtained in quiet and noise. Academic achievement and cognitive abilities were assessed with standardized measures.

RESULTS

Compared to controls, the trained group improved on measures of auditory processing and exhibited changes in cortical responses in quiet and in noise. In quiet, cortical responses reflected an accelerated maturational pattern; in background noise, cortical responses became more resistant to degradation. Brainstem responses did not change with training.

CONCLUSIONS

Children with learning problems who practiced with auditory training software exhibited plasticity of neural encoding of speech sounds at the cortical, but not subcortical, level of the auditory pathway. This plasticity was accompanied by improvement in behavioral performance.

SIGNIFICANCE

This study demonstrates that in learning-impaired children working with commercial auditory processing training programs affects both the perception and the cortical representation of sound.

Neural deficits in children with dyslexia ameliorated by behavioral remediation: evidence from functional MRI

Developmental dyslexia, characterized by unexplained difficulty in reading, is associated with behavioral deficits in phonological processing. Functional neuroimaging studies have shown a deficit in the neural mechanisms underlying phonological processing in children and adults with dyslexia. The present study examined whether behavioral remediation ameliorates these dysfunctional neural mechanisms in children with dyslexia. Functional MRI was performed on 20 children with dyslexia (8-12 years old) during phonological processing before and after a remediation program focused on auditory processing and oral language training. Behaviorally, training improved oral language and reading performance. Physiologically, children with dyslexia showed increased activity in multiple brain areas. Increases occurred in left temporo-parietal cortex and left inferior frontal gyrus, bringing brain activation in these regions closer to that seen in normal-reading children. Increased activity was observed also in right-hemisphere frontal and temporal regions and in the anterior cingulate gyrus. Children with dyslexia showed a correlation between the magnitude of increased activation in left temporo-parietal cortex and improvement in oral language ability. These results suggest that a partial remediation of language-processing deficits, resulting in improved reading, ameliorates disrupted function in brain regions associated with phonological processing and produces additional compensatory activation in other brain regions.

Electric brain responses obtained from newborn infants to changes in duration in complex harmonic tones

Event-related brain potentials of 10 full-term newborns in response to duration changes in complex, harmonic tones known to elicit prominent mismatch negativity (MMN) response in adults were investigated. Here we report that duration changes elicited prominent MMN responses in a 11 newborns tested. In contrast, MMN has been reported in as little as 50% of the infants in some previous studies using other sound attributes. When the infant MMN latency was compared with that obtained from adults, and 4- as well as 8-year-old children, it was found that the MMN latency was a bit later in newborns than in older age groups. This result is consistent with previous findings. The MMN amplitude, however, was surprisingly large in infants compared to older children.

Auditory sensory memory disorder in dyslexic adults as indexed by the mismatch negativity

Deficient temporal discrimination and vulnerability to masking effects caused by rapidly succeeding or simultaneous sounds might be one factor underlying the phonological difficulties in dyslexia. We evaluated cortical auditory discrimination in dyslexia by recording the mismatch negativity (MMN) for a simple pitch change, for an order reversal of tone pairs, and for tone-pair order reversals, with a third tone either preceding or following the tone pairs. It was found that when an additional tone followed the pairs the MMN amplitude was attenuated, suggesting elevated backward-masking effects in the auditory cortex of dyslexic individuals. In addition, the MMN elicited by pitch change was diminished over the left hemisphere of the dyslexic individuals suggesting left hemisphere auditory dysfunction. These results suggest impaired cortical discrimination of sounds and lowered tolerance for the masking effects of rapidly following sounds in dyslexia.

Temporal specificity of perceptual learning in an auditory discrimination task

Although temporal processing is used in a wide range of sensory and motor tasks, there is little evidence as to whether a single centralized clock or a distributed system underlies timing in the range of tens to hundreds of milliseconds. We investigated this question by studying whether learning on an auditory interval discrimination task generalizes across stimulus types, intervals, and frequencies. The degree to which improvements in timing carry over to different stimulus features constrains the neural mechanisms underlying timing. Human subjects trained on a 100- or 200-msec interval discrimination task showed an improvement in temporal resolution. This learning generalized to a perceptually distinct duration stimulus, as well as to the trained interval presented with tones at untrained spectral frequencies. The improvement in performance did not generalize to untrained intervals. To determine if spectral generalization was dependent on the importance of frequency information in the task, subjects were simultaneously trained on two different intervals identified by frequency. As a whole, our results indicate that the brain uses circuits that are dedicated to specific time spans, and that each circuit processes stimuli across nontemporal stimulus features. The patterns of generalization additionally indicate that temporal learning does not rely on changes in early, subcortical processing, because the nontemporal features are encoded by different channels at early stages.

Speaking clearly for children with learning disabilities: sentence perception in noise

This study compared the speech-in-noise perception abilities of children with and without diagnosed learning disabilities (LDs) and investigated whether naturally produced clear speech yields perception benefits for these children. A group of children with LDs (n = 63) and a control group of children without LDs (n = 36) were presented with simple English sentences embedded in noise. Factors that varied within participants were speaking style (conversational vs. clear) and signal-to-noise ratio (-4 dB vs. -8 dB); talker (male vs. female) varied between participants. Results indicated that the group of children with LDs had poorer overall sentence-in-noise perception than the control group. Furthermore, both groups had poorer speech perception with decreasing signal-to-noise ratio; however the children with LDs were more adversely affected by a decreasing signal-to-noise ratio than the control group. Both groups benefited substantially from naturally produced clear speech, and for both groups, the female talker evoked a larger clear speech benefit than the male talker. The clear speech benefit was consistent across groups; required no listener training; and, for a large proportion of the children with LDs, was sufficient to bring their performance within the range of the control group with conversational speech. Moreover, an acoustic comparison of conversational-to-clear speech modifications across the two talkers provided insight into the acoustic-phonetic features of naturally produced clear speech that are most important for promoting intelligibility for this population.

Evaluation of an exercise-based treatment for children with reading difficulties

An evaluation is reported of an exercise-based approach to remediation of dyslexia-related disorders. Pupils in three years of a Warwickshire junior school were screened for risk of literacy difficulty using the Dyslexia Screening Test (DST). The 35 children scoring 0.4 or over on the DST were divided randomly into two groups matched for age and DST score. One quarter of the participants had an existing diagnosis of dyslexia, dyspraxia or ADHD. Both groups received the same treatment at school but the intervention group used the DDAT exercise programme daily at home. Performance on the DST and specialist cerebellar/vestibular and eye movement tests were assessed initially and after six months. Cerebellar/vestibular signs were substantially alleviated following the exercise treatment whereas there were no significant changes for the control group. Even after allowing for the passage of time, there were significant improvements for the intervention group in postural stability, dexterity, phonological skill, and (one-tailed) for naming fluency and semantic fluency. Reading fluency showed a highly significant improvement for the intervention group, and nonsense passage reading was also improved significantly. Significantly greater improvements for the intervention group than the control group occurred for dexterity, reading, verbal fluency and semantic fluency. Substantial and significant improvements (compared with those in the previous year) also occurred for the exercise group on national standardized tests of reading, writing and comprehension. It is concluded that, in addition to its direct effects on balance, dexterity and eye movement control, the benefits of the DDAT exercise treatment transferred significantly to cognitive skills underlying literacy, to the reading process, and to standardized national literacy attainment tests.

Age-related improvements in auditory temporal resolution in reading-impaired children

Individuals with developmental dyslexia show impairments in processing that require precise timing of sensory events. Here, we show that in a test of auditory temporal acuity (a gap-detection task) children ages 6-9 years with dyslexia exhibited a significant deficit relative to age-matched controls. In contrast, this deficit was not observed in groups of older reading-impaired individuals (ages 10-11 years; 12-13 years) or in adults (ages 23-25 years). It appears, therefore, that early temporal resolution deficits in those with reading impairments may significantly ameliorate over time. However, the occurrence of an early deficit in temporal acuity may be antecedent to other language-related perceptual problems (particularly those related to phonological processing) that persist after the primary deficit has resolved. This result suggests that if remedial interventions targeted at temporal resolution deficits are to be effective, the early detection of the deficit and early application of the remedial programme is especially critical.

Experience effects on brain development: possible contributions to psychopathology

Researchers and clinicians are increasingly recognizing that psychological and psychiatric disorders are often developmentally progressive, and that diagnosis often represents a point along that progression that is defined largely by our abilities to detect symptoms. As a result, strategies that guide our searches for the root causes and etiologies of these disorders are beginning to change. This review describes interactions between genetics and experience that influence the development of psychopathologies. Following a discussion of normal brain development that highlights how specific cellular processes may be targeted by genetic or environmental factors, we focus on four disorders whose origins range from genetic (fragile X syndrome) to environmental (fetal alcohol syndrome) or a mixture of both factors (depression and schizophrenia). C.H. Waddington's canalization model (slightly modified) is used as a tool to conceptualize the interactive influences of genetics and experience in the development of these psychopathologies. Although this model was originally proposed to describe the 'canalizing' role of genetics in promoting normative development, it serves here to help visualize, for example, the effects of adverse (stressful) experience in the kindling model of depression, and the multiple etiologies that may underlie the development of schizophrenia. Waddington's model is also useful in understanding the canalizing influence of experience-based therapeutic approaches, which also likely bring about 'organic' changes in the brain. Finally, in light of increased evidence for the role of experience in the development and treatment of psychopathologies, we suggest that future strategies for identifying the underlying causes of these disorders be based less on the mechanisms of action of effective pharmacological treatments, and more on increased knowledge of the brain's cellular mechanisms of plastic change.

Auditory processing efficiency deficits in children with developmental language impairments

The "temporal processing hypothesis" suggests that individuals with specific language impairments (SLIs) and dyslexia have severe deficits in processing rapidly presented or brief sensory information, both within the auditory and visual domains. This hypothesis has been supported through evidence that language-impaired individuals have excess auditory backward masking. This paper presents an analysis of masking results from several studies in terms of a model of temporal resolution. Results from this modeling suggest that the masking results can be better explained by an "auditory efficiency" hypothesis. If impaired or immature listeners have a normal temporal window, but require a higher signal-to-noise level (poor processing efficiency), this hypothesis predicts the observed small deficits in the simultaneous masking task, and the much larger deficits in backward and forward masking tasks amongst those listeners. The difference in performance on these masking tasks is predictable from the compressive nonlinearity of the basilar membrane. The model also correctly predicts that backward masking (i) is more prone to training effects, (ii) has greater inter- and intrasubject variability, and (iii) increases less with masker level than do other masking tasks. These findings provide a new perspective on the mechanisms underlying communication disorders and auditory masking.

Effects of paired-pulse and repetitive stimulation on neurons in the rat medial geniculate body

Many behaviorally relevant sounds, including language, are composed of brief, rapid, repetitive acoustic features. Recent studies suggest that abnormalities in producing and understanding spoken language are correlated with abnormal neural responsiveness to such auditory stimuli at higher auditory levels [Tallal et al., Science 271 (1996) 81-84; Wright et al., Nature 387 (1997) 176-178; Nagarajan et al., Proc. Natl. Acad. Sci. USA 96 (1999) 6483-6488] and with abnormal anatomical features in the auditory thalamus [Galaburda et al., Proc. Natl. Acad. Sci. USA 91 (1994) 8010-8013]. To begin to understand potential mechanisms for normal and abnormal transfer of sensory information to the cortex, we recorded the intracellular responses of medial geniculate body thalamocortical neurons in a rat brain slice preparation. Inferior colliculus or corticothalamic axons were excited by pairs or trains of electrical stimuli. Neurons receiving only excitatory collicular input had tufted dendritic morphology and displayed strong paired-pulse depression of their large, short-latency excitatory postsynaptic potentials. In contrast, geniculate neurons receiving excitatory and inhibitory collicular inputs could have stellate or tufted morphology and displayed much weaker depression or even paired-pulse facilitation of their smaller, longer-latency excitatory postsynaptic potentials. Depression was not blocked by ionotropic glutamate, GABA(A) or GABA(B) receptor antagonists. Facilitation was unaffected by GABA(A) receptor antagonists but was diminished by N-methyl-D-aspartate (NMDA) receptor blockade. Similar stimulation of the corticothalamic input always elicited paired-pulse facilitation. The NMDA-independent facilitation of the second cortical excitatory postsynaptic potential lasted longer and was more pronounced than that seen for the excitatory collicular inputs. Paired-pulse stimulation of isolated collicular inhibitory postsynaptic potentials generated little change in the second GABA(A) potential amplitude measured from the resting potential, but the GABA(B) amplitude was sensitive to the interstimulus interval. Train stimuli applied to collicular or cortical inputs generated intra-train responses that were often predicted by their paired-pulse behavior. Long-lasting responses following train stimulation of the collicular inputs were uncommon. In contrast, corticothalamic inputs often generated long-lasting depolarizing responses that were dependent on activation of a metabotropic glutamate receptor. Our results demonstrate that during repetitive afferent firing there are input-specific mechanisms controlling synaptic strength and membrane potential over short and long time scales. Furthermore, they suggest that there may be two classes of excitatory collicular input to medial geniculate neurons and a single class of small-terminal corticothalamic inputs, each of which has distinct features.

[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.

Rapid auditory processing and MGN morphology in microgyric rats reared in varied acoustic environments

Adult male rats with induced microgyric lesions exhibit significant deficits in rapid auditory processing, as well as morphological alterations in the medial geniculate nucleus (MGN) of the thalamus. These findings are considered striking in light of similar anatomical and auditory processing anomalies in language disabled humans. Given evidence from clinical and animal studies that acoustic experience may alter sensory processing at behavioral and neurophysiological levels, the current study examined effects of developmental exposure to auditory stimulation on behavioral and anatomical indices in microgyric and sham rats. Stimulation (E7-P 70) included: (1). chronic white noise (80 dB) with standard housing; (2). 3 h/day of 78 dB filtered light classical music with social housing; or (3). standard acoustic environment (control) with standard housing. Microgyric effects on auditory processing and thalamic morphology were evident regardless of environmental condition. In sum, the effects of microgyria on brain and behavior appear to be robust, and largely orthogonal to any main effect of acoustic stimulation on auditory processing. These findings suggest that a more active form of acoustic stimulation (e.g., training) may be required to ameliorate the deleterious behavioral and anatomical consequences of focal microgyric lesions.

From Ear to Cortex: A Perspective on What Clinicians Need to Understand About Speech Perception and Language Processing

Phoneme-sized phonetic segments are often defined as the most basic unit of language organization. Two common inferences made from this description are that there are clear correlates to phonetic segments in the acoustic speech stream, and that humans have access to these segments from birth. In fact, well-replicated studies have shown that the acoustic signal of speech lacks invariant physical correlates to phonetic segments, and that the ability to recognize segmental structure is not present from the start of language learning. Instead, the young child must learn how to process the complex, generally continuous acoustic speech signal so that phonetic structure can be derived. This paper describes and reviews experiments that have revealed developmental changes in speech perception that accompany improvements in access to phonetic structure. In addition, this paper explains how these perceptual changes appear to be related to other aspects of language development, such as syntactic abilities and reading. Finally, evidence is provided that these critical developmental changes result from adequate language experience in naturalistic contexts, and accordingly suggests that intervention strategies for children with language learning problems should focus on enhancing language experience in natural contexts.

Auditory processing in children with dyslexia

BACKGROUND

It has been claimed that children with dyslexia show a general impairment in the processing of rapid auditory stimuli. However, most previous studies in this field have focused on children with language impairment or children who do not meet accepted criteria for dyslexia.

METHODS

In the present study, the processing of rapid non-verbal auditory stimuli (complex tones) was examined in a population-based sample of 24 children with dyslexia, 10 to 12 years of age, and a matched control group.

RESULTS

The dyslexia group showed reduced tone processing relative to the control group, with significant main effects of tone duration, inter-stimulus interval and task complexity. The deficit was not specific for temporal order errors, and could not be explained by differences in short-term memory or verbal IQ. However, correlations between tone processing and reading ability were generally low or absent.

CONCLUSION

Although a general processing deficit for rapid auditory stimuli in dyslexia was confirmed, its relevance for reading problems and hence for treatment programmes for dyslexia is questioned.

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.

The sensory basis of reading problems

Learning to read is much more difficult than learning to speak. Most children teach themselves to speak with little or no difficulty. Yet a few years later when they come to learn to read they have to be taught how to do it; they do not pick up reading by themselves. This is because we speak in words and syllables, but we write in phonemes. Syllables do not naturally break down into the sounds of letters and letter units (i.e., phonemes) because these do not correspond to physiologically distinct articulatory gestures (Liberman, Shankweiler, & Studdert-Kennedy, 1967). Alphabetic writing was only invented when people realized that syllables could be artificially divided into smaller acoustically distinguishable phonemes that could be represented by a small number of letters. But these distinctions are arbitrary cultural artifacts, and their mastery was originally confined to a select social class. And until about 100 years ago it did not matter much if the majority of people could not read; the acquisition of reading probably had no serious disadvantages. Reading requires the integration of at least two kinds of analysis (Castles & Coltheart, 1993; Ellis, 1984; Manis, Seidenberg, Doi, McBride-Chang, & Petersen, 1996; Morton, 1969; Seidenburg, 1993). First, the visual form of words, the shape of letters, their order in words, and common spelling patterns, which is termed their orthography, has to be processed visually. Their orthography yields the meaning of familiar words very rapidly without needing to sound them out. But for unfamiliar words, and all words are fairly unfamiliar to the beginning reader, the letters have to be translated into the speech sounds (i.e., phonemes) that they stand for, and then those sounds have to be melded together in inner speech to yield the word and its meaning. Reading exclusively by the phonological route is more time consuming than if words can be accessed directly without requiring phonological mediation.

Temporal processing and speech recognition in cochlear implant users

Although the speech recognition performance of cochlear implant patients has steadily improved in recent years, considerable variability remains in implant patient outcomes. Here, we report on a correlation between cochlear implant patients' auditory temporal processing and speech recognition abilities. Modulation detection thresholds were measured as a function of stimulation level; phoneme recognition was also assessed. Results showed marked individual differences in the shape and absolute sensitivity of subjects' modulation threshold functions. Statistical analysis revealed a strong correlation between phoneme recognition scores and subjects' mean modulation thresholds, demonstrating the contribution of temporal processing to implant speech perception. In correlating a basic psychophysical measure to speech performance, these results should contribute toward improved speech processor design and rehabilitation tools for cochlear implant patients.

Effect of solvent diffusion on the apomyoglobin-water interface

Few techniques can identify interactions between proteins and individual water molecules when the protein is in solution. The present work has sought to bridge the gap between the molecular level studies and the search for a physical property of the solution (bathing the proteins) that would regulate the protein hydration level. The properties of the solution were varied by adding nondenaturing solutes and solvents to the protein solutions and then studying their effect on the intrinsic fluorescence of apomyoglobin. The resolution of the tryptophan emission into the two component spectra corresponding to tryptophans W7 (accessible to the solvent) and W14 (buried in the protein matrix) has allowed us to probe two specific parts of the protein. Whereas W14 is not affected when the medium is altered, the analysis of W7 fluorescence has shown that cosolvent diffusion plays a dominant role in the mobility of water molecules near the protein surface.

Deciphering auditory processing disorders in children

APD is not a label for a unitary disease entity but rather a description of functional deficits [3]. It is a complex and heterogeneous group of auditory-specific disorders usually associated with a range of listening and learning deficits [3,4]. Underlying APD is a deficit observed in one or more of the auditory processes responsible for generating the auditory evoked potentials and the following behaviors: around localization and lateralization; auditory discrimination; auditory pattern recognition; temporal aspects of audition, including temporal resolution, masking, integration, and ordering; auditory performance with competing acoustic signals; and auditory performance with degraded acoustic signals [2]. Comprehensive assessment is necessary for the accurate differential diagnosis of APD from other "look-alike" disorders, most notably ADHD and language processing disorders. Speech-language pathologists, psychologists, educators, and physicians contribute to this more comprehensive assessment. The primary role of otolaryngologists is to evaluate and treat peripheral hearing disorders, such as otitis media. Children with APDs may present to an otolaryngologist, thus requiring the physician to make appropriate referral for assessment and intervention. Currently, diagnosis of APD is based on the outcomes of behavioral tests, supplemented by electroacoustic measures and, to a lesser extent, by electrophysiologic measures [1]. Intervention for APD focuses on improving the quality of the acoustic signal and the listening environment, improving auditory skills, and enhancing utilization of metacognitive and language resources [2]. Additional controlled case studies and single-subject and group research designs are needed to ascertain systematically the relative efficacy of various treatment and management approaches.

Effects of noise and cue enhancement on neural responses to speech in auditory midbrain, thalamus and cortex

Speech perception depends on the auditory system's ability to extract relevant acoustic features from competing background noise. Despite widespread acknowledgement that noise exacerbates this process, little is known about the neurophysiologic mechanisms underlying the encoding of speech in noise. Moreover, the relative contribution of different brain nuclei to these processes has not been fully established. To address these issues, aggregate neural responses were recorded from within the inferior colliculus, medial geniculate body and over primary auditory cortex of anesthetized guinea pigs to a synthetic vowel-consonant-vowel syllable /ada/ in quiet and in noise. In noise the onset response to the stop consonant /d/ was reduced or eliminated at each level, to the greatest degree in primary auditory cortex. Acoustic cue enhancements characteristic of 'clear' speech (lengthening the stop gap duration and increasing the intensity of the release burst) improved the neurophysiologic representation of the consonant at each level, especially at the cortex. Finally, the neural encoding of the vowel segment was evident at subcortical levels only, and was more resistant to noise than encoding of the dynamic portion of the consonant (release burst and formant transition). This experiment sheds light on which speech-sound elements are poorly represented in noise and demonstrates how acoustic modifications to the speech signal can improve neural responses in a normal auditory system. Implications for understanding neurophysiologic auditory signal processing in children with perceptual impairments and the design of efficient perceptual training strategies are also discussed.

Plastic changes in the central auditory system after hearing loss, restoration of function, and during learning

Traditionally the auditory system was considered a hard-wired sensory system; this view has been challenged in recent years in light of the plasticity of other sensory systems, particularly the visual and somatosensory systems. Practical experience in clinical audiology together with the use of prosthetic devices, such as cochlear implants, contributed significantly to the present view on the plasticity of the central auditory system, which was originally based on data obtained in animal experiments. The loss of auditory receptors, the hair cells, results in profound changes in the structure and function of the central auditory system, typically demonstrated by a reorganization of the projection maps in the auditory cortex. These plastic changes occur not only as a consequence of mechanical lesions of the cochlea or biochemical lesions of the hair cells by ototoxic drugs, but also as a consequence of the loss of hair cells in connection with aging or noise exposure. In light of the aging world population and the increasing amount of noise in the modern world, understanding the plasticity of the central auditory system has its practical consequences and urgency. In most of these situations, a common denominator of central plastic changes is a deterioration of inhibition in the subcortical auditory nuclei and the auditory cortex. In addition to the processes that are elicited by decreased or lost receptor function, the function of nerve cells in the adult central auditory system may dynamically change in the process of learning. A better understanding of the plastic changes in the central auditory system after sensory deafferentation, sensory stimulation, and learning may contribute significantly to improvement in the rehabilitation of damaged or lost auditory function and consequently to improved speech processing and production.

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.

Grammatical morphology and perception of synthetic and natural speech in children with specific language impairments

Studies investigating the relationship between the use of inflectional morphology and speech-perception abilities in children with SLI traditionally have employed synthetic speech stimuli. The purpose of this study was to replicate the findings reported in Leonard, McGregor, and Allen (1992) with an older group of children with SLI and to determine if the pattern of deficits seen for synthetic speech extends to perception of natural speech stimuli. The speech-perception abilities of 27 children between the ages of 6;11 and 8;11 (15 SLI and 12 NL) were compared using natural and synthetic versions of the [das]-[daS], [dabiba]-[dabuba], and [i]-[u] contrast pairs originally used in Leonard et al. The findings reported by Leonard et al. were replicated with synthetic speech but not for the natural speech. Use of inflectional morphology in obligatory contexts by the children with SLI was not significantly correlated with their perception abilities for any of the natural or synthetic speech-contrast pairs. Further, although both groups' ability to maintain the target contrast in memory declined over the span of the trials for all target contrasts for both natural and synthetic speech, the rate of decline did not differ significantly between the SLI and NL groups. Findings are discussed with respect to possible deficits in linking phonological representations to grammatical representations in children with SLI.

Perspectives on rehabilitation of individuals with cognitive impairment after brain injury: rationale for reconsideration of theoretical paradigms

BACKGROUND

The frequency of cognitive impairment associated with traumatic brain injury (TBI) has led to the widespread use of cognitive rehabilitation as a discrete rehabilitative service. This service has become controversial in part because of disagreements regarding its theoretical base and implementation procedures, and in part because of insufficient experimental support.

OBJECTIVE

We outline two paradigms for cognitive rehabilitation that are interestingly different, both theoretically and procedurally. These paradigms are defined in relation to the goals of intervention, orientation to assessment, modalities of treatment, organization of treatment, and logistics of service delivery (setting, content, and provider). A rationale for each paradigm is described.

CONCLUSION

We conclude with a call for (a) additional research into the effectiveness of interventions for individuals with cognitive impairment after TBI and (b) clinicians' thoughtful reflection on the foundations of their service.

A paradigm shift in neurorehabilitation

The practice of neurorehabilitation in the clinic has undergone a paradigm shift as a result of influences from basic and clinical research. I have identified six areas of knowledge that by advancing so rapidly have brought about this paradigm shift: first, the increased understanding of how the CNS is reorganised after training or injury; second, the knowledge of how declarative and procedural memory operates and how this can influence rehabilitation therapy; third, a greater appreciation of the chemical factors that promote learning and neural remodelling; fourth, the fact that computational neuroscience can teach us how complex behaviour can emerge from the interaction of thousands of neurons; fifth, the influence of evidence-based medicine on neurorehabilitation; and sixth, the importance of reliable outcome measures for both injury and treatment. These are young scientific disciplines that offer great opportunities for further research. The complexity of neurorehabilitation will also require greater attention to a substantially neglected problem, the incorporation of techniques that have been proven effective in clinical trials into routine and effective clinical practice.

Language transactions during development and intervention: theoretical implications for developmental neuroscience

Recent modeling of language development and intervention for children with disabilities has increasingly focused on the interactions between adults and children. These models have resulted in a number of recent advances in the behavioral treatment of language abilities in children with disabilities. Because these interventions are associated with substantial growth in a number of skills including speech, grammar and vocabulary, these paradigms may provide a useful model for studying neurological development of these aspects of language. The purpose of this paper is to discuss the potential neurodevelopmental ramifications of this type of theoretical model for facilitating language growth in children with and without disabilities. Indeed, because intervention can sometimes trigger rapid advances in language skills and presumably, associated neurological organization, this may prove to be a very useful paradigm for understanding the neurological correlates of language growth.

Duration processing in children as determined by time reproduction: implications for a few seconds temporal window

From research carried out over recent years using different experimental paradigms, it has become apparent that central information processing is temporally segmented into sequential units of a few seconds. This segmentation presumably reflects a neuronal process of temporal integration (TI) which automatically binds successive events into temporal units. Support for such TI comes, for example, from studies on temporal reproduction where standards up to approximately 2-3 s are reproduced veridically. Using this paradigm of temporal reproduction, we investigated the effect of normal cognitive development of sensory modality and of the range of presented standards on TI. Sixty children aged 6-7, 9-10 and 13-14 years reproduced visual or auditory standard durations ranged from 1 to 5.5 s or from 1 to 3 s. The results showed that durations of approximately 2 s were reproduced correctly, whereas those longer than 2.5 s were under-reproduced in the three age groups. For standards shorter than 2 s substantial age-related differences were revealed: the youngest group displayed significant over-reproduction comparing to older subjects. These observations indicate that the upper limit for TI is a stable feature across the different age groups. Furthermore an age-related modulation within the temporal window of the operating TI seems to be linked to cognitive development.

Transfer of learning across durations and ears in auditory frequency discrimination

Frequency-discrimination thresholds (FDTs) for 1-kHz tone pips with durations of 40, 100, and 200 msec were measured in the left and right ears of 10 normal-hearing listeners, before and after six 2-h frequency-discrimination training sessions involving, exclusively, the 200-msec duration and the right ear. In the trained ear, highly significant improvements in FDTs were observed at all durations. Further inspection of the data suggested complete generalization between 200 and 100 msec, but not at 40 msec. Posttraining FDTs were not found to differ between the two ears for the two untrained durations, but proved significantly smaller in the right (trained) than in the left (untrained) ear at the trained (200-msec) duration only. A control experiment involving 10 additional subjects allowed us to establish the absence of intrinsic differences in pretraining FDTs between the right and left ears. Overall, these findings indicate that frequency-discrimination learning generalizes widely across stimulus durations and across ears, but that part of the improvement is specific to the range of durations and to the ear used in training.

Brain mechanisms in normal and dyslexic readers

Developmental dyslexics, individuals with an unexplained difficulty reading, have been shown to have deficits in phonological processing -- the awareness of the sound structure of words -- and, in some cases, a more fundamental deficit in rapid auditory processing. In addition, dyslexics show a disruption in white matter connectivity between posterior and frontal regions. These results give continued support for a neurobiological etiology of developmental dyslexia. However, more research will be required to determine the possible causal relationships between these neurobiological disruptions and dyslexia.

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.

New treatments in neurorehabilitation founded on basic research

Recent discoveries about how the central nervous system responds to injury and how patients reacquire lost behaviours by training have yielded promising new therapies for neurorehabilitation. Until recently, this field had been largely static, but the current melding of basic behavioural science with neuroscience promises entirely new approaches to improving behavioural, perceptual and cognitive capabilities after neurological damage. Studies of phenomena such as cortical reorganization after a lesion, central nervous system repair, and the substantial enhancement of extremity use and linguistic function by behavioural therapy, support this emerging view. The ongoing changes in rehabilitation strategies might well amount to an impending paradigm shift in this field.

Auditory temporal processing deficits in children with periventricular brain injury

The present study investigated whether auditory temporal processing deficits are related to the presence and/or the severity of periventricular brain injury and the reading difficulties experienced by extremely low birthweight (ELBW: birthweight <1000 g) children. Results indicate that ELBW children with mild or severe brain lesions obtained significantly lower scores on a test requiring auditory temporal order judgments than ELBW children without periventricular brain injury or children who were full-term. Structural equation modeling indicated that a model in which auditory temporal processing deficits predicted speech sound discrimination and phonological processing ability provided a better fit for the data than did a second model, which hypothesized that auditory temporal processing deficits are associated with poor reading abilities through a working memory deficit. These findings suggest that an impairment in auditory temporal processing may contribute to the reading difficulties experienced by ELBW children.

Deficits in language-mediated mental operations in patients with schizophrenia

We found previously that a subgroup of schizophrenic patients who passed screening tests of attentional competence showed memory deficits on word memory tasks, but were comparable with controls on tone memory tasks. To better understand the nature of language-specific memory deficits in this subgroup of patients, the present experiment was designed to bypass early perceptual processing of verbal material and determine if patients continue to show impaired performance on verbal memory tasks. Patients who passed the screening tests ('discriminator' patients; DSz) received four serial position tasks. In two, familiar sounds or line drawings were presented and subjects were required to remember the word associated with each stimulus item. In the other two, subjects received hard-to-label auditory and visual stimuli (birdsongs or snowflakes).DSz patients showed large memory deficits compared with controls when required to remember words associated with the familiar sounds or drawings, providing clear evidence of deficits in verbal memory processes independent of sensory processing of verbal stimuli. The interaction between diagnosis and labeling was highly significant, confirming that these patients have particular difficulty with verbal as opposed to non-verbal memory. This was particularly striking on the auditory tests where two patients out-performed all controls on the birdsong test, but were below all controls on the easy-to-label sounds test. The verbal memory tests were easier than the non-verbal memory tests for controls, thus deconfounding task difficulty and deficit specificity.

Auditory development and the role of experience

The human ear is functionally mature shortly after birth, but the central auditory system continues to develop for at least the first decade of life. Current interest focuses on the relation between the very late developing aspects of hearing and other aspects of cognition and behaviour. While active neural input to the brain is essential during the very early stages of development, auditory experience is now thought to be a powerful influence on central function throughout an individual's lifespan. Studies of sound localization and hearing with two ears have shown the capacity of the auditory system to adapt to altered environmental cues, even into adulthood. This environmental influence may either be harmful, as during conductive deafness, or beneficial, as evidenced by the positive outcomes of auditory training.

Impaired processing of rapid stimulus sequences in dyslexia

Apart from their reading difficulties, dyslexic subjects often suffer from a variety of subtle sensory and motor deficits. Whether these deficits have a causal relationship to the reading disorder, form additional risk factors, or are totally independent of the reading problem, is under vivid debate. In this article, we review the evidence and suggest that 'sluggish attentional shifting' (SAS) can account for the impaired processing of rapid stimulus sequences in dyslexia. Within this novel framework attention-related prolongation of input chunks is decisive for many small deficits found in dyslexic subjects.

Multisensory prior entry

Despite 2 centuries of research, the question of whether attending to a sensory modality speeds the perception of stimuli in that modality has yet to be resolved. The authors highlight weaknesses inherent in this previous research and report the results of 4 experiments in which a novel methodology was used to investigate the effects on temporal order judgments (TOJs) of attending to a particular sensory modality or spatial location. Participants were presented with pairs of visual and tactile stimuli from the left and/or right at varying stimulus onset asynchronies and were required to make unspeeded TOJs regarding which stimulus appeared first. The results provide the strongest evidence to date for the existence of multisensory prior entry and support previous claims for attentional biases toward the visual modality and toward the right side of space. These findings have important implications for studies in many areas of human and animal cognition.

Newborn and preschool predictors of second-grade reading scores: an evaluation of categorical and continuous scores

This study examined how the development of foundation skills in speech perception, language, short-term memory, and family demographics and activities in the home environment influence the development of reading skills. Data from 96 children participating in a longitudinal research project were used. It was hypothesized that measures of specific foundation skills in the preschool period and measures of family demographics and home environment could be used to identify children's reading abilities. As expected, most of the foundation skills were found to be related to and predictive of reading scores. Event-related potential (ERP) measures of speech perception, which have previously been found to be predictive of reading abilities, and measures of family and home activities and language measures were related to reading scores. Verbal short-term memory scores contributed little to the prediction of reading scores. These variables influenced the results whether they were used to discriminate reading groups or to predict a continuum of reading scores, but there were large differences in the amount of variance accounted for. More variance was accounted for in the group analyses than in the continuum analyses.

Language deficits, localization, and grammar: evidence for a distributive model of language breakdown in aphasic patients and neurologically intact individuals

Selective deficits in aphasic patients' grammatical production and comprehension are often cited as evidence that syntactic processing is modular and localizable in discrete areas of the brain (e.g., Y. Grodzinsky, 2000). The authors review a large body of experimental evidence suggesting that morpho-syntactic deficits can be observed in a number of aphasic and neurologically intact populations. They present new data showing that receptive agrammatism is found not only over a range of aphasic groups, but is also observed in neurologically intact individuals processing under stressful conditions. The authors suggest that these data are most compatible with a domain-general account of language, one that emphasizes the interaction of linguistic distributions with the properties of an associative processor working under normal or suboptimal conditions.