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

Orienting asymmetries in rhesus monkeys: the effect of time-domain changes on acoustic perception

Humans exhibit left-hemisphere dominance for processing spoken language, a species-specific acoustic signal characterized by a suite of spectro-temporal parameters. Some nonhuman primates (genus Macaca) also exhibit left-hemisphere dominance for processing their species-specific vocalizations, as evidenced by right-ear biases in orienting and reaction-time studies, and more damaging effects from left- than right-hemisphere lesions. Little, however, is known about the acoustic features underlying such biases. We conducted field playback experiments on adult rhesus monkeys, Macaca mulatta, to determine whether asymmetries in perception (measured as an orienting bias) are sensitive to changes in the temporal characteristics of their calls. If the observed right-ear bias for perceiving conspecific calls (Hauser & Andersson 1994, Proceedings of the National Academy of Sciences, U.S.A., 91, 3946-3948) depends upon particular acoustic parameters, then experimental manipulations beyond the species-typical range of signal variation will cause a change in perceptual asymmetry, either reversing the pattern (i.e. right to left ear ) or wiping it out (i.e. no asymmetry). We presented manipulated and unmanipulated exemplars of three pulsatile call types within the rhesus repertoire: an affiliative signal 'grunt', an alarm signal 'shrill bark', and a mating signal 'copulation scream'. Signal manipulations involved either (1) a reduction of the interpulse interval to zero or the population minimum or (2) an expansion of the interpulse interval to the population maximum, or two times the maximum. For the grunt and shrill bark, manipulations of interpulse interval outside the range of natural variation either eliminated the orienting bias or caused a shift from right- to left-ear bias. For the copulation scream, however, a right-ear bias was observed in response to all stimuli, manipulated and unmanipulated. Results show that for some call types within the repertoire, temporal properties such as interpulse interval provide significant information to listeners about whether the signal is from a conspecific or not. We interpret the orienting bias as evidence that hemispheric asymmetries underly this perceptual effect.Copyright 1998 The Association for the Study of Animal Behaviour.

Short-term memory and language outcomes after extreme prematurity at birth

The performance of 26 children (3;0-4;0 years) who were born before 32 weeks gestation was compared with the performance of 26 full-term children on a range of short-term memory and language measures. The measures tested vocabulary, expressive language, phonological short-term memory, and general nonverbal ability. Preterm children scored more poorly across the full range of measures. The mildly depressed performance of the preterm group on the short-term memory and language measures was attributable to the large deficits on these tests shown by a subgroup of approximately one third of preterm children identified as being "at risk" for persisting language difficulties using the Bus Story Test (Bishop & Edmundson, 1987). The findings indicate that preterm birth and associated hazards may constitute a significant risk factor for specific language impairment in a sizable minority of children.

Temporal and spectral sensitivity of complex auditory neurons in the nucleus HVc of male zebra finches

Complex vocalizations, such as human speech and birdsong, are characterized by their elaborate spectral and temporal structure. Because auditory neurons of the zebra finch forebrain nucleus HVc respond extremely selectively to a particular complex sound, the bird's own song (BOS), we analyzed the spectral and temporal requirements of these neurons by measuring their responses to systematically degraded versions of the BOS. These synthetic songs were based exclusively on the set of amplitude envelopes obtained from a decomposition of the original sound into frequency bands and preserved the acoustical structure present in the original song with varying degrees of spectral versus temporal resolution, which depended on the width of the frequency bands. Although both excessive temporal or spectral degradation eliminated responses, HVc neurons responded well to degraded synthetic songs with time-frequency resolutions of approximately 5 msec or 200 Hz. By comparing this neuronal time-frequency tuning with the time-frequency scales that best represented the acoustical structure in zebra finch song, we concluded that HVc neurons are more sensitive to temporal than to spectral cues. Furthermore, neuronal responses to synthetic songs were indistinguishable from those to the original BOS only when the amplitude envelopes of these songs were represented with 98% accuracy. That level of precision was equivalent to preserving the relative time-varying phase across frequency bands with resolutions finer than 2 msec. Spectral and temporal information are well known to be extracted by the peripheral auditory system, but this study demonstrates how precisely these cues must be preserved for the full response of high-level auditory neurons sensitive to learned vocalizations.

Sensitive periods for visual calibration of the auditory space map in the barn owl optic tectum

Previous studies have identified sensitive periods for the developing barn owl during which visual experience has a powerful influence on the calibration of sound localization behavior. Here we investigated neural correlates of these sensitive periods by assessing developmental changes in the capacity of visual experience to alter the map of auditory space in the optic tectum of the barn owl. We used two manipulations. (1) We equipped owls with prismatic spectacles that optically displaced the visual field by 23 degrees to the left or right, and (2) we restored normal vision to prism-reared owls that had been raised wearing prisms. In agreement with previous behavioral experiments, we found that the capacity of abnormal visual experience to shift the tectal auditory space map was restricted to an early sensitive period. However, this period extended until later in life (approximately 200 d) than described previously in behavioral studies (approximately 70 d). Furthermore, unlike the previous behavioral studies that found that the capacity to recover normal sound localization after restoration of normal vision was lost at approximately 200 d of age, we found that the capacity to recover a normal auditory space map was never lost. Finally, we were able to reconcile the behaviorally and neurophysiologically defined sensitive periods by taking into account differences in the richness of the environment in the two sets of experiments. We repeated the behavioral experiments and found that when owls were housed in a rich environment, the capacity to adjust sound localization away from normal extended to later in life, whereas the capacity to recover to normal was never lost. Conversely, when owls were housed in an impoverished environment, the capacity to recover a normal auditory space map was restricted to a period ending at approximately 200 d of age. The results demonstrate that the timing and even the existence of sensitive periods for plasticity of a neural circuit and associated behavior can depend on multiple factors, including (1) the nature of the adjustment demanded of the system and (2) the richness of the sensory and social environment in which the plasticity is studied.

Levels of analysis in health science. A framework for integrating sociobehavioral and biomedical research

One of the principal goals of the Office of Behavioral and Social Sciences Research at the National Institutes of Health is to facilitate interdisciplinary research between social, behavioral, and biomedical scientists. The purpose of this paper is to provide a framework for such interdisciplinary health research. The essence of this framework is the concept of levels of analysis in the health sciences. These levels include the social/environment, behavioral/psychological, organ systems, cellular, and molecular. The interdependence of these five levels of analysis suggests that advances in the health sciences may be accelerated by a more integrated, multilevel approach to research. The principles of integrated, multilevel research are outlined, and examples of research that support this approach are presented. Finally, some of the activities of the Office of Behavioral and Social Sciences Research that will further interdisciplinary research across levels of analysis are summarized.

Recovery of cognitive functions following nonprogressive brain injury

It has recently become clear that the adult human brain is capable of more plasticity than previously thought. Investigations into the natural history of change following brain injury demonstrate that partial recovery of function can and does occur. Furthermore, there is increasing evidence that intervention through re-training or provision of compensatory memory aids can result in improved cognitive functioning.

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.

Adult cortical dynamics

There are many influences on our perception of local features. What we see is not strictly a reflection of the physical characteristics of a scene but instead is highly dependent on the processes by which our brain attempts to interpret the scene. As a result, our percepts are shaped by the context within which local features are presented, by our previous visual experiences, operating over a wide range of time scales, and by our expectation of what is before us. The substrate for these influences is likely to be found in the lateral interactions operating within individual areas of the cerebral cortex and in the feedback from higher to lower order cortical areas. Even at early stages in the visual pathway, cells are far more flexible in their functional properties than previously thought. It had long been assumed that cells in primary visual cortex had fixed properties, passing along the product of a stereotyped operation to the next stage in the visual pathway. Any plasticity dependent on visual experience was thought to be restricted to a period early in the life of the animal, the critical period. Furthermore, the assembly of contours and surfaces into unified percepts was assumed to take place at high levels in the visual pathway, whereas the receptive fields of cells in primary visual cortex represented very small windows on the visual scene. These concepts of spatial integration and plasticity have been radically modified in the past few years. The emerging view is that even at the earliest stages in the cortical processing of visual information, cells are highly mutable in their functional properties and are capable of integrating information over a much larger part of visual space than originally believed.

Temporal-order discrimination for selected auditory and visual stimulus dimensions

Thresholds for the discrimination of temporal order were determined for selected auditory and visual stimulus dimensions in 10 normal-adult volunteers. Auditory stimuli consisted of binary pure tones varying in frequency or sound pressure level, and visual stimuli consisted of binary geometric forms varying in size, orientation, or color. We determined the effect of psychophysical method and the reliability of performance across stimulus dimensions. Using a single-track adaptive procedure, Experiment 1 showed that temporal-order thresholds (TOTs) varied with stimulus dimension, being lowest for auditory frequency, intermediate for size, orientation, and auditory level, and longest for color. Test performance improved over sessions and the profile of thresholds across stimulus dimensions had a modest reliability. Experiment 2 used a double-interleaved adaptive procedure and TOTs were similarly ordered as in Experiment 1. However, TOTs were significantly lower for initially ascending versus descending tracks. With this method, the reliability of the profile across stimulus dimensions and tracks was relatively low. In Experiment 3, psychometric functions were obtained for each of the stimulus dimensions and thresholds were defined as the interpolated 70.7% correct point. The relative ordering of TOTs was similar to those obtained in the first two experiments. Non-monotonicities were found in some of the psychometric functions, with the most prominent being for the color dimension. A cross-experiment comparison of results demonstrates that TOTs and their reliability are significantly influenced by the psychophysical method. Taken together, these results support the notion that the temporal resolution of ordered stimuli involves perceptual mechanisms specific to a given sensory modality or submodality.

Speech perception in children with specific reading difficulties (dyslexia)

Many experimental studies over the last two decades have suggested that groups of children who suffer significant delay in reading also show a weakness in phoneme discrimination and identification. In order to look further at the relation between type of reading deficit, auditory acuity, and speech discrimination, a group of 13 children with specific reading difficulty (SRD), 12 chronological-age controls, and 12 reading-age controls were tested on a battery of speech-perceptual, psychoacoustic, and reading tests. A sub-group of children with Specific Reading Difficulty (SRD) were poor at speech discrimination tests, whereas the rest of the SRD group performed within norms. For this sub-group, discrimination performance was particularly poor for consonant contrasts differing in a single feature that was not acoustically salient, and problems were encountered with nasal and fricative contrasts as wells with stop contrasts. These children did not differ from controls in their performance on non-speech psychoacoustic tasks. An evaluation is made of the reported phonemic awareness skills of beginning readers with regard to speech-processing issues which may help in understanding what factors are important in reading development.

Cerebral lateralisation and rate of maturation

Multifactorial inheritance applied to brain development implies a large continuum of normal variation with deviation from the norm at the extremes of maturational rate. The greater population of neurons, greater arborization of neural networks and excessive synaptic density in early maturation imply that adaptability (plasticity) is a main advantage, as opposed to a deficit in adaptability associated with the reduced number of neurons, reduced connectivity and reduced synaptic density in late slow maturation. It is hypothesised that Planum Temporale (PT) asymmetry and hand-preference predict the rate of CNS maturation as does the cognitive profile on the Wechsler Adult Intelligence Scale (WAIS): PT leftward asymmetry, right-handedness and a left-hemisphere cognitive advantage signifies early fast maturation: PT rightward asymmetry, left-handedness and a right-hemisphere cognitive advantage signify late maturation, while PT symmetry and ambilaterality represent rates of maturation in between. The slower development of males implies a male predominance in disorders affecting late maturers: Developmental Dyslexia (DD) with a predominance of rightward PT asymmetry/symmetry, left-handedness and multiple functional deficits, as well as excessive regressive events confirmed on PT/MRI. Schizophrenia, hypothesised to be a disorder in late maturers, is distinguished by rightward asymmetry/symmetry. Left-handedness and DD are common as is prior delayed development supporting excessive regressive events as do the findings on PT/MRI. To reduce the risk of DD and schizophrenia requires a reduction in late maturation through the enhancement of maturational rate by optimal nutrition before and during pregnancy and later.

Trying to Make Sense of Developmental Language Disorders

In this article, I share my thoughts concerning what children with developmental language disorders should be called, how they should be defined, and how we might differentiate children with specific language impairment (SLI) from other children with developmental language disorders. Among other things, I attempt to show why a lack of congruence between clinical and research constructs should be expected.

Researchers and clinicians use different identification criterion and procedures because clinical and educational objectives are different from research objectives. While recognizing these differences, I suggest several possible ways to differentiate a subgroup of children with SLI from the general population of children with developmental language disorders without using nonverbal IQ. Even if researchers are able to identify this unique group of children, clinicians may never embrace the SLI construct.

In the best of all possible worlds, clinicians would be familiar with how researchers define SLI and appreciate the value of research that attempts to identify distinct subgroups of children with developmental language disorders. Researchers, in this ideal world, would recognize and acknowledge the lack of congruence between the research populations of SLI and the larger clinical population of children with developmental language disorders.

Reading ability and processing in Duchenne muscular dystrophy and spinal muscular atrophy

We analysed the reading abilities and processing of 21 children with Duchenne muscular dystrophy (DMD), 11 matched children suffering from spinal muscular atrophy (SMA) and 42 children receiving normal education. The principal result observed was that the DMD children exhibited a reading age which was significantly lower than the SMA children compared with their chronological age. These learning disabilities were not related to a deficit in non-verbal performance intelligence, but psycholinguistic evaluation showed a deficit in verbal intelligence, especially in the Similarities and Arithmetic WISC-R subtests, in phonological abilities, oral word repetition, and in digit span score. The results for the DMD children were heterogeneous, and ranged from normal to greater or lesser involvement. In an attempt to clarify the nature of this reading impairment in DMD children, the three groups (DMD, SMA, and normal control children) were tested by reading aloud a list of single words and non-words. The DMD children were significantly impaired in reading non-words, suggesting reading disability similar to dysphonetic dyslexia, the most frequent subtype of developmental dyslexia. These results are discussed in the light of psychometric data available for our DMD population and in the light of previous studies. The practical consequences of diagnosis on rehabilitation are very important. The precise description of the cognitive deficits seen in DMD is of value for future clinical and genetic studies.

Brain morphology in children with specific language impairment

The planum temporale and pars triangularis have been found to be larger in the left hemisphere than the right in individuals with normal language skills. Brain morphology studies of individuals with developmental language disorders report reversed asymmetry or symmetry of the planum, although the bulk of this research has been completed on adults with dyslexia. Pars triangularis has not been studied in the developmental language impaired population. In this study, magnetic resonance imaging (MRI) was used for quantitative comparisons of the planum temporale (Wernicke's area) and pars triangularis (Broca's area) in children with specific language impairment (SLI) and children with normal language skills. The subjects were 11 children with SLI and 19 age- and sex-matched controls between 5.6 and 13.0 years old. Each subject received a neurolinguistic battery of tests and a high resolution volumetric MRI scan. Major results were that (a) pars triangularis was significantly smaller in the left hemisphere of children with SLI, and (b) children with SLI were more likely to have rightward asymmetry of language structures. Furthermore, anomalous morphology in these language areas correlated with depressed language ability. These findings support the hypothesis that language impairment is a consequence of an underlying neurobiological defect in areas of the brain known to subserve language.

Evolution and revolution in child psychiatry: ADHD as a disorder of adaptation

Current knowledge about early plasticity and children's responsiveness to environmental modifications as well as the atheoretical nature of current nosological systems necessitate alternative models to explain the phenomena of childhood behavioral and emotional disturbances. Evolutionary biology provides one such framework. It organizes data from the behavioral and cognitive sciences and parallels similar efforts in other areas of medicine and biology. Through an evolutionary biological lens, some mental disorders are better viewed as an adaptive response to early pathogenic environments and/or reflect the optimization of brain function to some environments at the cost of poorer response to the demands of other environments. As an example, the authors examine attention-deficit/hyperactivity disorder (ADHD) in relation to evolutionary theories of psychology and biology and clarify the potentially adaptive nature of characteristics of inattention, impulsivity, and motoric hyperactivity, depending on the nature of child's environments. Reframing ADHD characteristics according to evolutionary theory has important treatment implications for clinicians and offers researchers opportunities for novel scientific discoveries.

Follow-up study of a right- and a left-hemispherectomized child: implications for localization and impairment of language in children

Two hemispherectomized girls, one operated on the right, the other on the left, were followed from time of surgery until 9 and 10 years of age and compared with respect to course of language acquisition following surgery. At conclusion of follow-up, receptive and expressive language, phoneme perception and production, and sentence processing of the two hemispherectomized children were compared with those of two control groups of similar age, one developing language normally, the other language-impaired. The left-hemispherectomized child's abilities were similar to those of the language-impaired children; the right-hemispherectomized child's abilities resembled those of the language-normal children. Implications for localization of developmental anomalies in language-impaired children are discussed.

Effect of sign task on speech timing in simultaneous communication

The purpose of this investigation was to study the effect of the signing task on temporal features of speech during simultaneous communication (SC). The effects of three independent variables: (a) communication mode (speech only vs. SC); (b) sign task demand (base vs. elaborated signs); and (c) type of sign movement (kinetic vs. morphokinetic) were studied on five dependent variables: (a) word duration; (b) sentence duration; (c) diphthong duration; (d) interword interval before signed experimental word (IWIB); and (e) interword interval after signed experimental word (IWIA). Audio recordings were made of 12 normal hearing, experienced sign language users speaking experimental words that varied in sign task demand and movement under SC and speech only (SO) conditions. Results indicated longer sentence durations for SC than SO and longer anticipatory durations of IWIB and diphthong before signed words, especially those using signs with greater task demand or with movements including hand shape change. IWIA only lengthened for SC vs. SO with no further effect of sign task demand or movement. These results indicate finite effects of sign task demand and movement on pause and segment durations before the sign but not as strong an effect as has been reported for increased finger spelling task length.

Cognitive neuropsychology and developmental disorders: uncomfortable bedfellows

Cognitive neuropsychology provides a theoretical framework and methods that can be of value in the study of developmental disorders, but the "dissociation" logic at the centre of this approach is not well suited to the developmental context. This is illustrated with examples from specific language impairment. Within the developing language system there is ample evidence for interaction between levels of representation, with modularity emerging in the course of development. This means that one typically is seeking to explain a complex pattern of associated impairments, rather than highly selective deficits. For instance, a selective impairment in auditory processing can have repercussions through the language system and may lead to distinctive syntactic deficits that are seen in written as well as spoken language. Changes in the nature of representations and in the relationships between components of a developing system mean that cross-sectional data at a single point in development may be misleading indicators of the primary deficit. Furthermore, traditional cognitive neuropsychology places a disproportionate emphasis on representational (competence) deficits, with processing (performance) deficits being relatively neglected. Methods for distinguishing these two kinds of impairment are discussed, as well as other approaches for elucidating the underlying nature of developmental disorders.

Verbal dichotic listening in boys at risk for behavior disorders

OBJECTIVE

The association between deficits in verbal processing skills and disruptive psychopathology remains one of the most frequently replicated findings in all of child psychiatry. This study uses a dichotic consonant-vowel listening test to examine the potential neural basis for this association.

METHOD

A series of 87 young boys recruited from a sample at risk for disruptive disorders received standardized psychiatric, neuropsychological, and language skills assessments. Approximately 1 year later, these boys received a reassessment of their psychiatric status and a test that assesses the neural basis of language-processing ability, a dichotic consonant-vowel listening test.

RESULTS

Disruptive psychopathology predicted reduced right ear accuracy for dichotic syllables, indicative of a deficit in left hemisphere processing ability. Deficits in reading and language ability also correlated with right ear accuracy for dichotic syllables.

CONCLUSIONS

Boys with disruptive behavior disorders, relative to at-risk but nondisruptive boys, exhibit a deficit in verbal processing abilities on dichotic listening tasks. This deficit in verbal processing ability is also manifested as low scores on standardized tests of reading achievement and language comprehension.

Context-sensitive synaptic plasticity and temporal-to-spatial transformations in hippocampal slices

Hippocampal slices are used to show that, as a temporal input pattern of activity flows through a neuronal layer, a temporal-to-spatial transformation takes place. That is, neurons can respond selectively to the first or second of a pair of input pulses, thus transforming different temporal patterns of activity into the activity of different neurons. This is demonstrated using associative long-term potentiation of polysynaptic CA1 responses as an activity-dependent marker: by depolarizing a postsynaptic CA1 neuron exclusively with the first or second of a pair of pulses from the dentate gyrus, it is possible to "tag" different subpopulations of CA3 neurons. This technique allows sampling of a population of neurons without recording simultaneously from multiple neurons. Furthermore, it reflects a biologically plausible mechanism by which single neurons may develop selective responses to time-varying stimuli and permits the induction of context-sensitive synaptic plasticity. These experimental results support the view that networks of neurons are intrinsically able to process temporal information and that it is not necessary to invoke the existence of internal clocks or delay lines for temporal processing on the time scale of tens to hundreds of milliseconds.

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

Many people with developmental dyslexia have difficulty perceiving stop consonant contrasts as effectively as other people and it has been suggested that this may be due to perceptual limitations of a temporal nature. Accordingly, we predicted that perception of such stimuli by listeners with dyslexia might be improved by stretching them in time-equivalent to speaking slowly. Conversely, their perception of the same stimuli ought to be made even worse by compressing them in time-equivalent to speaking quickly. We tested 15 children with dyslexia on their ability to identify correctly consonant-vowel-consonant (CVC) stimuli that had been stretched or compressed in the time domain. We also tested their perception of the same CVC stimuli after the formant transitions had been stretched or compressed in the frequency domain. Contrary to our predictions, we failed to find any systematic improvement in their performance with either manipulation. We conclude that simple manipulations in the time and frequency domains are unlikely to benefit the ability of people with dyslexia to discriminate between CVCs containing stop consonants.

Scalp potentials evoked by amplitude-modulated tones in dyslexia

We recorded the far-field EEG potential evoked by amplitude modulation of acoustic stimuli (the amplitude modulation following response, AMFR) in adults with developmental dyslexia and in a matched control group of adults with no history of reading problems. The mean AMFR recorded from participants with dyslexia was significantly smaller than that recorded from members of the control group. In contrast, the amplitude of the click-evoked auditory brainstem response (ABR) was not significantly different between participant groups. Also, there was no difference between participant groups in the latency of the AMFR or ABR. The reduced AMFR in listeners with dyslexia may reflect impaired ability of the auditory system to follow rapid changes in stimulus energy, a cue believed to be important in the perception of speech.

Child Development and Neuroscience

Although developmental psychology and developmental neuroscience share interests in common problems (e.g., the nature of thought, emotion, consciousness), there has been little cross-fertilization between these disciplines. To facilitate such communication, we discuss 2 major advances in the developmental brain sciences that have potentially profound implications for under standing behavioral development. The first concerns neuroimaging, and the second concerns the molecular and cellular events that give rise to the developing brain and the myriad ways in which the brain is modified by both positive and negative life experiences. Recurring themes are that (1) critical, new knowledge of behavioral development can be achieved by considering the neurobiological mechanisms that guide and influence child development, and (2) these neurobiological mechanisms are in turn influenced by behavior.

Learning perceptual skills: behavioral probes into adult cortical plasticity

Recent studies of the improvement of perceptual performance as a function of training - perceptual learning - have provided new insights into the neuronal substrates of this type of skill learning in the adult brain. Issues such as where in the brain, when and under what conditions practice-related changes occur are under investigation. The results of these studies suggest that a behaviorally relevant degree of plasticity is retained in the adult cortex, even within early, low-level representations in sensory and motor processing streams. The acquisition and retention of skills may share many characteristics with the functional plasticity subserving early-life learning and development. While the specificity of learning provides localization constraints, an important clue to the nature of the underlying neuronal changes is the time course of learning.

Learning disorders with a special emphasis on reading disorders: a review of the past 10 years

OBJECTIVE

To review the past 10 years of clinical and research reports on learning disorders.

METHOD

The most common and best-researched type of learning disorder is reading disability, which is the focus of this review. A selective review of the literature from Psychological Abstracts and Index Medicus from 1985 to the present was conducted. This review focused on conceptual and methodological issues, current assessment practices, epidemiology, correlates of brain function, biological factors, predictors of reading achievement, core deficits, comorbidity reading development and instructional approaches, treatment, and outcome.

RESULTS

Definitional issues, still unresolved, bedevil the field with the debate between those for and those against discrepancy definitions of reading disabilities. Nevertheless considerable progress has been made. Phonological processing problems are now considered the main core deficit responsible for reading disabilities. Correlates of brain function and possible genetic factors are noted. Comorbidity with externalizing and internalizing disorders is described, and some theories for the overlap are identified. Studies on the comorbidity with internalizing disorders are lacking. Good assessment practice and promising approaches to remediation are identified. Unless a concurrent disorder is present, the use of medication for the treatment of reading disabilities should be considered experimental. Favorable outcomes are dependent on initial severity and a supportive home and school environment.

CONCLUSIONS

Much progress has been made in our understanding of learning disabilities, especially in reading disabilities. Resolution of definitional and conceptual issues will greatly assist research into assessment, treatment, and long-term outcome of learning disabilities with and without concurrent psychiatric disorders. Further research into the nature, extent, and correlates of comorbid learning disabilities and their treatment is much needed.

An examination of the morpheme BE in children with specific language impairment: the role of contractibility and grammatical form class

This study examined the production of the morpheme BE, focusing on the influence of contractibility, the relationship between copula and auxiliary forms, and the occurrence of non-omission errors. Language samples collected from children with SU and from normal language learners at equivalent MLU levels were analyzed. Three levels of contractibility were examined: contractible, syntactically uncontractible, and phonetically uncontractible. Contractible contexts were produced significantly more accurately than uncontractible contexts by both groups. There was no difference between the two forms of uncontractibility. Furthermore, there were no significant interactions between language status and contractibility, suggesting that contractibility influenced both groups equally. Copula forms were produced more consistently than auxiliary. There was no interaction between BE type and language status. The groups did not differ in proportion or type of non-omission error. The results are discussed in relation to accounts of morphological deficits in SU.

Remediation of children with developmental language disorders

There is no single approach to intervention in children with developmental language disorders. Remedial approaches differ in that they are based on differing theoretical perspectives. Four theoretical frames are reviewed. Neuropsychologically driven remediation, which tailors intervention to a child's profile of cognitive and linguistic strengths and weakness, is emphasized. Concrete examples of compensatory techniques suited to specific profiles are presented.

The neural system of language: structure and development

Recent neuroimaging and neuropsychological research in adults and infants suggests that the neural system for language is widely distributed and shares organizational principles with other cognitive systems in the brain. Connectionist modelling has clarified that networks operating with associative mechanisms can display properties typically associated with genetically predetermined and dedicated symbolic functions.

A Estrutura Temporal da Consciência

Podemos ainda estar bastante longe de construir um modelo neurobiológico dos estados mentais conscientes sem incorrer nas insuficiências do reducionismo ou do funcionalismo. Alguns passos importantes foram entretanto dados neste sentido. O principal deles refere-se à idéia de que o estudo da dinâmica temporal de grupos neuronais pode fornecer alguma pista sobre os blocos funcionais utilizados na construção da experiência subjetiva consciente. Há cerca de 30 anos Pöppel vem trabalhando com um modelo de organização temporalmente descontínua da atividade mental consciente, o qual compreende dois mecanismos oscilatórios, de alta e de baixa frequência. O primeiro relaciona-se à definição de eventos e o segundo a sua integração em um momento psicológico. Os mecanismos da consciência equivalem aos que tornam esta sucessão de momentos temporais discretos possível. A compreensão dos mecanismos neuronais destas periodicidades e de sua relação com o processamento de informação está apenas começando.

Neurobiology of speech perception

The mechanisms by which human speech is processed in the brain are reviewed from both behavioral and neurobiological perspectives. Special consideration is given to the separation of speech processing as a complex acoustic-processing task versus a linguistic task. Relevant animal research is reviewed, insofar as these data provide insight into the neurobiological basis of complex acoustic processing in the brain.

Cognitive neuropsychology and its application to children

Cognitive neuropsychology has been used successfully in the analysis of adult neuropsychological disorders in both verbal and nonverbal domains. When applied to children, it aims to construct models on the basis of functional lesions manifest within developing systems and provides a theoretical framework within which patterns of intact and deficient skills can be charted over time. These patterns constrain possible underlying models. In highlighting potential individual differences in the acquisition of skills and indicating intact skills within subjects, cognitive neuropsychology may also enable a precise description of the locus of difficulty and potential circumventory routes for remediation around it. The theoretical assumptions of cognitive neuropsychology and issues relevant to its methodology are discussed, including the terminology and principles of modularity, the significance of individual differences and the use of case studies, the dynamics of developing systems, current views on plasticity, and distinctions between developmental and acquired disorders. The application of cognitive neuropsychology to children is discussed in relation to three cognitive areas: face recognition disorders, language disorders and arithmetical disorders. These illustrate the similarities that there are between many developmental cognitive neuropsychological disorders and those seen in adults following brain injury. Models derived from studies of adults are helpful in enabling understanding of both face recognition disorders and arithmetical disorders in childhood. Within language systems, a variety of different types of disorder are evident, which not only relate to receptive and productive difficulties but differentially affect the core components of the language system. All of the disorders discussed illustrate the limitations of functional plasticity in development. In each case, there is not a generalised deficit resulting from degradation of capabilities independent of task requirements. Rather, there are focal and selective disorders which affect subcomponents of cognitive systems. In some cases, genetic factors may constrain compensatory mechanisms.

Double dissociation, modularity, and distributed organization

Müller argues that double dissociations do not imply underlying modularity of the cognitive system, citing neural networks as examples of fully distributed systems that can give rise to double dissociations. We challenge this claim, noting that suchdouble dissociations typically do not “scale-up,” and that even some singledissociations can be difficult to account for in a distributed system.

Familial language impairment: The evidence

Müller argues that general cognitive skills and linguistic skills are not necessarily independent. However, cross-linguistic evidence from an inherited specific language disorder affecting productive rules suggests significant degrees of modularity, innateness, and universality of language. Confident claims about the overall nature of such a complex system still await more interdisciplinary research.

Innateness, autonomy, universality, and the neurobiology of regular and irregular inflectional morphology

Müller's goal of bringing neuroscience to bear on controversies in linguistics is laudable. However, some of his specific proposals about innateness and autonomy are misguided. Recent studies on the neurobiology of regular and irregular inflectional morphology indicate that these two linguistic processes are subserved by anatomically and physiologically distinct neural subsystems, whose functional organization is likely to be under direct genetic control rather than assembled by strictly epigenetic factors.

Biology of language: Principle predictions and evidence

Müller's target article aims to summarize approaches to the question of how language elements (phonemes, morphemes, etc.) and rules are laid down in the brain. However, it suffers from being too vague about basic assumptions and empirical predictions of neurobiological models, and the empirical evidence available to test the models is not appropriately evaluated. (1) In a neuroscientific model of language, different cortical localizations of words can only be based on biological principles. These need to be made explicit. (2) Evidence for and against word class differences could be evaluated more rigorously. (3) All (and only) humans are able to learn languages with complex syntactic structures; it is, therefore, not appropriate to deny innateness and universality of syntactic principles. The real question appears to be the following: Which neurobiological principles are the linguistic principles based on?

Müller's conclusions and linguistic research

Because Müiller fails to distinguish between two senses of the term “autonomy,” there is a danger that his results will be misinterpreted by both linguists and neuroscientists. Although he may very well have been successful in refuting one sense of autonomy, he may actually have helped to provide an explanation for the correctness of autonomy in its other sense.

Speaking of language: Thoughts on associations

Müller attempts to downplay cases of dissociation between language and cognition as evidence against the modularity of language. We review cases of associations between verbal and nonverbal abilities as further evidence against the notion of language as an autonomous subsystem. We also point out a discrepancy between his proposal of homologies between nonhuman primates' communication and human language and recent proposals on the evolution of language.

Auditory temporal resolution in specifically language-impaired and age-matched children

Recently there has been renewed interest in the auditory processing capabilities of children with specific language impairment. In this study, eight children with specific language impairment and eight nonimpaired, age-matched peers completed a task to assess temporal resolution abilities. Children were asked to detect a tone in three masking conditions wherein the masker contained silent gaps of 0 msec., 40 msec., or 64 msec. in duration. Thresholds were measured in each masking condition at 500 Hz and 2000 Hz. Across the groups, thresholds decreased (improved) significantly as a function of increases in the duration of the gaps. Children in the two groups exhibited remarkably similar thresholds for the three masking conditions. However, children with specific language impairment required a significantly greater number of ascending trials to achieve the threshold criterion than did age-matched children. Results suggest that language-impaired children perceive temporal aspects of acoustic stimuli as well as their normally developing peers. Attentional mechanisms may play an important role in the difficulties they exhibit in auditory processing.

It's a far cry from speech to language

We agree with Müller's epigenetic view of evolution and ontogeny and applaud his multilevel perspective. With him, we stress the importance in ontogeny of progressive specialisation rather than prewired structures. However, we argue that he slips from “speech” to “language” and that, in seeking homologies, these two levels need to be kept separate in the analysis of evolution and ontogeny.

A worthy enterprise injured by overinterpretation and misrepresentation

The synthetic position adopted by Müller is weakened by a large number of overinterpretations and misrepresentations, together with a caricatured view of innateness and modularity.

The epigenesis of regional specificity

Chomskyian claims of a genetically hard-wired and cognitively autonomous “universal grammar” are being promoted by generative linguistics as facts about language to the present day. The related doctrine of an evolutionary discontinuity in language emergence, however, is based on misconceptions about the notions of homology and preadaptation. The obvious lack of equivalence between symbolic communicative capacities in existing nonhuman primates and human language does not preclude common roots. Normal and disordered language development is strongly influenced by the genome, but there is no evidence for the existence of specific genes underlying “universal grammar.” In the mature brain, stages of language processing can be distinguished and “first-pass” syntactic analyses appear to precede semantic decoding. However, this partial seriality – as well as behavioral and clinical dissociations between lexical and functional categories – can be best described, not in terms of serially activated and discrete modules, but in terms of classes of cell assemblies that differ in their distributional properties. Whereas cell assemblies involved in semantic interpretation (“content word” assemblies) are widely distributed and are generally less vulnerable to focal lesion, those involved in structural decoding (functor assemblies) are primarily distributed within the left perisylvian cortices and are selectively vulnerable to left perisylvian lesion. These distributional differences are explained in terms of the perceptuomotor components involved in the acquisition of relevant representations. The emerging “motivated” or “toposemantic” brain regional specificity can only be accommodated with “soft” and maturational versions of modularity. The failure to reproduce double dissociations in current connectionist models is due to overly simple neuroscientific assumptions, notably that of overall equipotentiality. Linguistic models should not be expected to be “implemented” in the brain, but need to be constrained by neuroscientific evidence on how biological brains function.

Pluripotentiality, epigenesis, and language acquisition

Müller provides a valuable synthesis of neurobiological evidence on the epigenetic development of neural structures involved in language acquisition. The pluripotentiality of developing neural tissue crucially constrains linguistic/cognitive theorizing about supposedly innate neural mechanisms and contributes significantly to our understanding of experience–dependent processes involved in language acquisition. Without this understanding, any proposed explanation of language acquisition is suspect.

Autonomy and its discontents

Müller's review of the neuroscientific evidence undermines nativist claims for autonomous syntax and the argument from the poverty of the stimulus. Generativists will appeal to data from language acquisition, but here too there is growing evidence against the nativist position. Epigenetic naturalism, the developmental alternative to nativism, can be extended to epigenetic socionaturalism, acknowledging the importance of sociocultural processes in language and cognitive development.

A polyglot perspective on dissociation

Evidence is presented from a polyglot savant to suggest that double dissociations between linguistic and nonverbal abilities are more important than Müller's target article implies. It is also argued that the special nature of syntax makes its assimilation to other aspects of language or to nonhuman communication systems radically implausible.

Auditory temporal coding in dyslexia

Developmental dyslexia is generally believed to result from impaired linguistic processing rather than from deficits in low-level sensory function. Challenging this view, we studied the perception of non-verbal acoustic stimuli and low-level auditory evoked potentials in dyslexic adults. Compared with matched controls, dyslexics were selectively impaired in tasks (frequency discrimination and binaural unmasking) which rely on decoding neural discharges phase-locked to the fine structure of the stimulus. Furthermore, this ability to use phase-locking was related to reading ability. In addition, the evoked potential reflecting phase-locked discharges was significantly smaller in dyslexics. These results demonstrate a low-level auditory impairment in dyslexia traceable to the brainstem nuclei.

Auditory neurophysiologic responses and discrimination deficits in children with learning problems

Children with learning problems often cannot discriminate rapid acoustic changes that occur in speech. In this study of normal children and children with learning problems, impaired behavioral discrimination of a rapid speech change (/dalpha/versus/galpha/) was correlated with diminished magnitude of an electrophysiologic measure that is not dependent on attention or a voluntary response. The ability of children with learning problems to discriminate another rapid speech change (/balpha/versus/walpha/) also was reflected in the neurophysiology. These results indicate that some children's discrimination deficits originate in the auditory pathway before conscious perception and have implications for differential diagnosis and targeted therapeutic strategies for children with learning disabilities and attention disorders.