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

Deaf poor readers' pattern reversal visual evoked potentials suggest magnocellular system deficits: implications for diagnostic neuroimaging of dyslexia in deaf individuals

Deafness and developmental dyslexia in the same individual may jointly limit the acquisition of reading skills for different underlying reasons. A diagnostic marker for dyslexia in deaf individuals must therefore detect the presence of a neurobiologically based dyslexia but be insensitive to the ordinary developmental influences of deafness on reading skill development. We propose that the functional status of the magnocellular visual system in deaf individuals is potentially such a marker. We present visual evoked potential (VEP) evidence that adult deaf poor readers as a group display magnocellular system deficits not observed in deaf good readers. We recorded pattern-reversal VEPs to high- and low-contrast checkerboard stimuli, which primarily activate the parvocellular and magnocellular pathways, respectively. Principal components analysis of these VEPs produced a time-ordered sequence of three early components that displayed interactions between reading skill and stimulus contrast across multiple scalp recording sites. Deaf poor readers displayed an abnormal absence of contrast-sensitive VEP responses at occipital sites during early visual processing (75 ms poststimulus), whereas deaf good readers showed the expected early contrast-sensitive occipital VEP responses. Over the subsequent 225 ms, the occipital VEP behavior of deaf poor readers closely approximated that of deaf good readers. The VEPs of deaf poor readers were apparently characterized by delayed responses to low-contrast stimuli compared with deaf good readers. Our results provide the first neurobiological evidence that developmental dyslexia exists within the deaf population and is associated with the same underlying magnocellular system deficit that has been observed in hearing dyslexics. Direct neural imaging of the status of the magnocellular visual system in deaf individuals may eventually provide differential diagnosis of developmental dyslexia in the deaf population.

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.

Auditory processing and the development of language and literacy

This paper considers evidence for basic auditory processing impairments associated with dyslexia and specific language impairment, against a back-drop of findings from studies of the normal development of auditory and phonological processing. A broad range of auditory impairments have been implicated in the aetiology of these language-learning disorders, including deficits in discriminating the temporal order of rapid sequences of auditory signals, elevated thresholds for frequency discrimination and for detection of amplitude and frequency modulation, impaired binaural processing and increased susceptibility to backward masking. Current evidence is inconsistent, but suggests that not all children with language difficulties have non-verbal auditory processing impairments, and for those that do, the impact on language development is poorly understood. Some implications for clinical practice are discussed.

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.

Nonconscious temporal cognition: learning rhythms implicitly

Two experiments demonstrate that people can implicitly learn rhythms. Participants responded to a series of fast-paced beeps by pressing a key as soon as possible after each beep. They were not told that the duration (180, 450, or 1,125 msec) between each keypress and the next beep was specified by a repeating sequence. In both experiments, participants responded significantly faster to predictable, sequenced timing than to random timing but did not show more knowledge of the sequence than did control participants on explicit memory measures. This dissociation was obtained even with an explicit memory test in Experiment 2 that maintained the same context and response metric as the implicit task to maximize the transfer of relevant knowledge. Implications for temporal cognition are discussed.

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.

Aetiology and clinical presentations of auditory processing disorders--a review

Auditory processing disorders may have detrimental consequences on a child's life, if undiagnosed and untreated. We review causes of auditory processing disorders in order to raise clinical awareness. Auditory processing disorders may present against a background of neurological disease or developmental disorders, as well as in isolation. Clinicians need to be aware of potential causes and implications of auditory processing disorders.

Persistent and specific influences of early acoustic environments on primary auditory cortex

This study demonstrates that the adult form of 'tonotopic maps' of sound frequency in the rat primary auditory cortex (A1) arises from parallel developmental processes involving two cortical zones: the progressive differentiation and refinement of selectively tone-responsive receptive fields within an initially broadly-tuned posterior zone, and the progressive loss of tone-evoked, short-latency response over an initially large, very broadly tuned anterior zone. The formation of tonotopic maps in A1 was specifically influenced by a rat pup's early acoustic environments. Exposure to pulsed tones resulted in accelerated emergence and an expansion of A1 representations of those specific tone frequencies, as well as a deteriorated tonotopicity and broader-than-normal receptive fields. Thus, auditory experiences during early postnatal development are important in shaping the functional development of auditory cortical representations of specific acoustic environments.

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.

The neural basis of perceptual learning

Perceptual learning is a lifelong process. We begin by encoding information about the basic structure of the natural world and continue to assimilate information about specific patterns with which we become familiar. The specificity of the learning suggests that all areas of the cerebral cortex are plastic and can represent various aspects of learned information. The neural substrate of perceptual learning relates to the nature of the neural code itself, including changes in cortical maps, in the temporal characteristics of neuronal responses, and in modulation of contextual influences. Top-down control of these representations suggests that learning involves an interaction between multiple cortical areas.

The mismatch negativity as an index of temporal processing in audition

OBJECTIVES

The relation of the mismatch negativity (MMN) elicitation with behavioral stimulus discrimination as well as the replicability of the MMN was evaluated for intervals between paired tones.

METHODS

The MMN, obtained in a passive oddball paradigm in two sessions separated by 4-21 days and behavioral responses (button presses to target stimuli) in a separate session were recorded from 10 adult healthy subjects. The standard stimulus (P=0.79) was a tone pair separated by a 120 ms silent inter-stimulus interval (ISI) and the deviant stimuli were tone pairs with an ISI of 100, 60, and 20 ms (P=0.07 for each).

RESULTS

The 20 and 60 ms ISI deviant tone pairs elicited a significant MMN during both recording sessions and they were also behaviorally discriminated, whereas neither did the 100 ms ISI deviant pair elicit significant MMN nor was it behaviorally discriminated. Furthermore, there was a significant correlation between the MMN and reaction times to the 20 and 60 ms ISI deviant pairs. The 20 ms ISI deviant stimulus elicited highly replicable MMNs (r=0.75), whereas the less well discriminated 60 ms ISI deviant pair did not (r=0.60).

CONCLUSIONS

The MMN reflects discrimination accuracy of temporal sound intervals. Furthermore, when the physical difference between the standard and deviant tone pair in the temporal domain is large, it is elicited with high reliability.

Plastic neural changes and reading improvement caused by audiovisual training in reading-impaired children

This study aimed at determining whether audiovisual training without linguistic material has a remediating effect on reading skills and central auditory processing in dyslexic children. It was found that this training resulted in plastic changes in the auditory cortex, indexed by enhanced electrophysiological mismatch negativity and faster reaction times to sound changes. Importantly, these changes were accompanied by improvement in reading skills. The results indicate that reading difficulties can be ameliorated by special training programs and, further, that the training effects can be observed in brain activity. Moreover, the fact that the present training effects were obtained by using a program including no linguistic material indicates that dyslexia is at least partly based on a general auditory perceptual deficit.

Measuring temporal resolution in infants using mismatch negativity

We show that the mismatch negativity (MMN) component of the event-related potential can be used to measure auditory temporal resolution in human infants. Infrequent stimuli with silent gaps of 4, 8, or 12 ms modulated the P2 component, generated MMN, and produced a P3a-like positivity. The data indicate that within-channel gap detection thresholds at 6 months are essentially at adult levels under conditions of little adaptation. Since MMN is elicited without attention and does not require a behavioural response, it can be measured similarly across the lifespan. We are now in a position to study the development of cross-channel temporal resolution and adaptation effects in infancy, and to examine how these abilities in infancy relate to later language acquisition.

Is there a relationship between speech and nonspeech auditory processing in children with dyslexia?

A group of 8 young teenagers with dyslexia were compared to age-matched control participants on a number of speech and nonspeech auditory tasks. There were no differences between the control participants and the teenagers with dyslexia in forward and simultaneous masking, nor were there any differences in frequency selectivity as indexed by performance with a bandstop noise. Thresholds for backward masking in a broadband noise were elevated for the teenagers with dyslexia as a group. If this deficit in backward masking had an influence on speech perception, we might expect the perception of "ba" versus "da" to be affected, as the crucial second formant transition is followed by a vowel. On the other hand, as forward masking is not different in the two groups, we would expect the perception of "ab" versus "ad" to be unaffected, as the contrastive second formant transition is preceded by a vowel. Overall speech identification and discrimination performance for these two contrasts was superior for the control group but did not differ otherwise. Thus, the clear group deficit in backward masking in the group with dyslexia has no simple relationship to the perception of crucial acoustic features in speech. Furthermore, the deficit for nonspeech analogues of the speech contrasts (second formants in isolation) was much less marked than for the speech sounds, with 75% of the listeners with dyslexia performing equivalently to control listeners. The auditory deficit cannot therefore be simply characterized as a difficulty in processing rapid auditory information. Either there is a linguistic/phonological component to the speech perception deficit, or there is an important effect of acoustic complexity.

The mismatch negativity in evaluating central auditory dysfunction in dyslexia

The mismatch negativity (MMN), a brain response elicited by a discriminable change in any repetitive aspect of auditory stimulation even in the absence of attention, has been widely used in both basic and clinical research during recent years. The fact that the MMN reflects the accuracy of auditory discrimination and that it can be obtained even from unattentive subjects makes it an especially attractive tool for studying various central auditory-system dysfunctions both in adults and children. In this review, we will discuss the applicability of the MMN to studies in dyslexia, which is currently thought, in the majority of the cases, to primarily result either from a dysfunction of the phonological system or a more general auditory deficit. Recent evidence indicates that the MMN enables one to determine which aspects of auditory information are deficiently processed in dyslexia. The MMN might also be helpful in the early definition of the dyslexia type, which would make it possible to start correctly-targeted training programmes before any major learning delays occur. Furthermore, the MMN holds promise of showing plastic changes in the brain of dyslexic individuals underlying the alleviation or remediation of dyslexia in the course of a successful training programme.

The "temporal processing deficit" hypothesis in dyslexia: new experimental evidence

The notion that developmental dyslexia may result from a general, nonspecific, defect in perceiving rapidly changing auditory signals is a current subject of debate (so-called "temporal processing deficit" hypothesis). Thirteen phonological dyslexics (age 10-13 years) and 10 controls matched for chronological and reading 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 relevance of the temporal deficit hypothesis, the task also included two additional conditions where either the two stimuli were artificially slowed or the interstimulus interval was expanded. 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 no significant improvement occurred when increasing the interstimulus interval. Finally dyslexics' performances, especially on the slowed condition, were found correlated with several tests of phonological processing (phoneme deletion, rhyme judgment, and nonword spelling tasks). These results lend support to the general temporal deficit theory of dyslexia.

Intensive training of phonological skills in progressive aphasia: a model of brain plasticity in neurodegenerative disease

Three patients with a typical syndrome of nonfluent primary progressive aphasia (Mesulam's syndrome) were trained daily with a remediation protocol including auditory exercises specifically designed to involve several aspects of phonological processing, a domain known to be specifically affected in the condition. The speech content of the exercises was based on the temporal theory of phonological processes according to which increasing the duration of formant transition should facilitate phoneme discrimination and phoneomic awareness. Significantly improved performance on the trained tasks was demonstrated in the three patients. Improvement further generalized to other tasks such as nonword repetition and reading. We conclude that such results (1) argue for using intensive focused therapy of language impairment in neurodegenerative disorders, (2) may constitute a good model of brain plasticity in neurodegenerative disorders in general, and (3) support theories of phonological processing emphasizing temporal features of the auditory signal.

Neurobiologic responses to speech in noise in children with learning problems: deficits and strategies for improvement

OBJECTIVES

Some children with learning problems (LP) experience speech-sound perception deficits that worsen in background noise. The first goal was to determine whether these impairments are associated with abnormal neurophysiologic representation of speech features in noise reflected at brain-stem and cortical levels. The second goal was to examine the perceptual and neurophysiological benefits provided to an impaired system by acoustic cue enhancements.

METHODS

Behavioral speech perception measures (just noticeable difference scores), auditory brain-stem responses, frequency-following responses and cortical-evoked potentials (P1, N1, P1', N1') were studied in a group of LP children and compared to responses in normal children.

RESULTS

We report abnormalities in the fundamental sensory representation of sound at brain-stem and cortical levels in the LP children when speech sounds were presented in noise, but not in quiet. Specifically, the neurophysiologic responses from these LP children displayed a different spectral pattern and lacked precision in the neural representation of key stimulus features. Cue enhancement benefited both behavioral and neurophysiological responses.

CONCLUSIONS

Overall, these findings contribute to our understanding of the preconscious biological processes underlying perception deficits and may assist in the design of effective intervention strategies.

Adaptive learning: interventions for verbal and motor deficits

Advances in basic and clinical neuroscience are uniting to form new optimism for treatment and rehabilitation of persons with a variety of neurologic disorders. Both cognitive and motor systems have shown remarkable degrees of plasticity in response to incoming stimuli. Understanding the brain (and spinal cord) capacity for change will lead to new topics for research as well as new approaches to rehabilitation. Adaptive learning has been shown to be a fundamental part of the developmental process and has been used in remediation of a variety of language difficulties. Using such principles to approach motor functions also is showing promise. Expanding these observations to encompass other areas of disease and rehabilitation is an area for further research. Interdisciplinary approaches including the fields of computer technology, imaging, and genetic analysis will provide new tools. Contribution of new concepts within adaptive learning must address such topics as the relation between motor and sensory responses, measures that accurately indicate cognitive health, the brain and spinal cord areas involved in particular learning tasks, the optimal time windows for intervention, and the importance of behavior and motivation in treatment and rehabilitation.

Neuropsychologische Interventionsstrategien am Beispiel der umschriebenen Entwicklungsstörungen der Sprache und der Motorik

Zusammenfassung. Für höhere mentale Funktionen ist das unbeeinträchtigte Zusammenwirken mehrerer einzelner Prozesse erforderlich. Mittels neuropsychologischer Interventionsansätze bei Kindern wird versucht, bei Funktionsbeeinträchtigungen, die sich auf in Entwicklung befindliche Systeme auswirken, gestörte Prozesse sowie deren Zusammenwirken spezifisch zu beeinflussen. Eine neuropsychologische Interventionsstrategie bei umschriebenen Entwicklungsstörungen beinhaltet die Erfassung des Profils von Stärken und Schwächen, die Identifizierung des oder der gestörten Prozesse des betreffenden funktionellen Systems, die Anwendung spezifischer neuropsychologischer Interventionen unter Verwendung geeigneter Instruktionsstrategien und verhaltensmodifzierender Maßnahmen sowie den kompensatorischen Einsatz intakter Prozesse oder Funktionen. Bei Patienten mit umschriebenen Entwicklungsstörungen der Sprache wurde eine Beeinträchtigung der auditiven Verarbeitung kurzer bzw. in schneller Abfolge präsentierter Stimuli gezeigt. Mittels computergestützter neuropsychologischer Trainingsprogramme konnten auditive Diskrimination und Segmentierung, Phonemverarbeitung und Sprachverständnis deutlich verbessert werden ( Merzenich et al., 1996 ; Tallal et al., 1996 ). Zur Behandlung von Kindern mit umschriebenen Entwicklungsstörungen der Motorik wurden sensorische Integration und Kinästhetisches Training eingesetzt. Für beide Behandlungsverfahren wird zwar postuliert, daß Funktionsverbesserungen über die Veränderung spezifischer Prozesse erreicht werden, es konnte auch eine gewisse Effektivität belegt werden, welche jedoch weitgehend unspezifisch ist und wahrscheinlich auf allgemeinen Wirkfaktoren beruht.

Relating selective brain damage to impairments with voicing contrasts

Research is reviewed concerning the performance of several neurological groups on the perception and production of voicing contrasts in speech. Patients with cerebellar damage, Parkinson's disease, specific language impairment, Broca's aphasia, apraxia, and Wernicke's aphasia have been reported to be impaired in the perception and articulation of voicing. The types of deficits manifested by these neurologically impaired groups in creating and discriminating voicing contrasts are discussed and the respective contributions of separate neural areas are identified. A model is presented specifying the level of phonemic processing thought to be impaired for each patient group and critical tests of the model's predictions are identified.

Human auditory steady-state responses to tones independently modulated in both frequency and amplitude

OBJECTIVE

Independent amplitude and frequency modulation (IAFM) of a carrier tone uses two different modulating frequencies, one for amplitude modulation (AM) and one for frequency modulation (FM). This study measured the human steady-state responses to multiple IAFM tones. The first question was whether the IAFM responses could be recorded without attenuation of the AM and FM components. The second question was whether IAFM stimuli would provide a more effective demonstration of responses at intensities near threshold than the responses to AM tones. The third question was whether the responses to multiple IAFM stimuli would relate to the discrimination of words at different intensities.

DESIGN

Multiple AM, FM, or IAFM stimuli were presented simultaneously. Responses were recorded between the vertex and the neck and analysed in the frequency domain. The first experiment compared IAFM responses with AM and FM responses. The second experiment compared IAFM responses with AM responses between intensities 20 to 50 dB SPL. The third experiment related the IAFM responses to the discrimination of monosyllabic words at intensities between 20 and 70 dB SPL.

RESULTS

Steady-state responses to the individual component of the IAFM stimuli were clearly recognizable although attenuated a little (14%) from the responses to AM or FM alone. Using IAFM stimuli was not different than simply using AM stimuli when trying to recognize responses at low intensities. The number of responses detected during multiple IAFM stimulation and the amplitudes of these responses correlated significantly with word discrimination.

CONCLUSIONS

IAFM of a carrier using two different modulating frequencies (one for AM and one for FM) elicits separate AM and FM responses that are relatively independent of each other. These separate responses can be used to detect whether a particular carrier has been processed in the cochlea, but they are not as effective as measuring responses to carriers that have been modulated in both amplitude and frequency at the same modulation frequency (mixed modulation). The detectability of eight different responses (four AM and four FM) to an IAFM stimuli relates well to the ability of subjects to discriminate words. IAFM stimuli therefore show promise as an objective test for assessing suprathreshold hearing.

Perceptual discrimination of speech sounds in developmental dyslexia

Experiments previously reported in the literature suggest that people with dyslexia have a deficit in categorical perception. However, it is still unclear whether the deficit is specific to the perception of speech sounds or whether it more generally affects auditory function. In order to investigate the relationship between categorical perception and dyslexia, as well as the nature of this categorization deficit, speech specific or not, the discrimination responses of children who have dyslexia and those of average readers to sinewave analogues of speech sounds were compared. These analogues were presented in two different conditions, either as nonspeech whistles or as speech sounds. Results showed that children with dyslexia are less categorical than average readers in the speech condition, mainly because they are better at discriminating acoustic differences between stimuli belonging to the same category. In the nonspeech condition, discrimination was also better for children with dyslexia, but differences in categorical perception were less clear-cut. Further, the location of the categorical boundary on the stimulus continuum differed between speech and nonspeech conditions. As a whole, this study shows that categorical deficit in children with dyslexia results primarily from an increased perceptibility of within-category differences and that it has a speech-specific component. These findings may have profound implications for learning and re-education.

Auditory temporal processing deficit in dyslexia is associated with enhanced sensitivity in the visual modality

Developmental dyslexia has been associated with a deficit in temporal processing, but it is controversial whether the postulated deficit is pansensory or limited to the auditory modality. We present psychophysical assessment data of auditory and visual temporal processing abilities in children with dyslexia. While none of the dyslexic children displayed temporal processing abnormalities in the visual sensory modality, dyslexics with poor auditory temporal scores reached high-level visual performance. Our results do not confirm the hypothesis of a general temporal processing deficit for dyslexia but suggest that limitations in auditory temporal processing might be compensated for by a well-functioning visual sensory modality.

Does dyslexia develop from learning the alphabet in the wrong hemisphere? A cognitive neuroscience analysis

A new perspective is described which views developmental dyslexia as the outcome of learning to write the alphabet in the nondominant (right) hemisphere. The letter-level and whole-word subtypes of dyslexia are seen as differing responses adopted to cope with this predicament. Striking similarities between dyslexics and callosotomy patients in the allocation of covert attention to lateralized stimuli provide direction for integrating a diversity of dyslexic research within this framework. This synthesis, together with information from pure alexia, brain activation, and reading research, lends insight into the neural circuitry of the compensatory strategies adopted by the two dyslexic subtypes.

Event-related potentials during auditory language processing in congenitally blind and sighted people

While behavioral studies have documented delayed language acquisition in blind children, other studies have revealed better speech discrimination abilities for blind than sighted adults. Several brain imaging studies have provided evidence for cortical reorganization due to visual deprivation but the cerebral organization of language in blind humans is not known yet. We hypothesized that the increasing specialization of language systems normally observed during development may not take place to the same degree in blind individuals since posterior visual areas do not receive their adequate input. On the other hand, we hypothesized that blind people, due to their greater reliance upon the auditory language signal, may process speech faster than sighted people. To test these assumptions, event-related potentials were recorded while 11 congenitally blind and 11 sighted adults matched in age, gender, handedness and education were engaged in a language task. Participants listened to sentences in order to decide after each sentence if it was meaningful or not. Incongruous sentence-final words elicited an N400 effect in both groups. The N400 effect had a left-lateralized fronto-central scalp distribution in the sighted but a symmetric and broad topography in the blind. Furthermore, the N400 effect started earlier in the blind than in the sighted. Closed class compared to open class sentence middle words elicited a more pronounced late negativity in the blind than in the sighted. These results suggest that blind people process auditory language stimuli faster than sighted people and that some language functions may be reorganized in the blind.

An emergent account of language impairments in children with SLI: implications for assessment and intervention

While current theoretical accounts of language impairments in children with specific language impairment (SLI) provide clear direction with regard to intervention goal setting, these same accounts say little with regard to the intervention process. Current developments in connectionist modeling and the extension of principles of dynamical systems theory to cognitive and language development have resulted in a new theory of language development known as emergentism. In contrast to traditional formal linguistic accounts, the emergentist view holds that language is a dynamic evolving system that can be represented as a distribution of probabilistic information. Language acquisition, from this perspective, emerges from the child's simultaneous integration of multiple acoustic, linguistic, social and communicative cues within the context of the communicative interaction. An alternative account of SLI grounded within this emergentist view is presented, and preliminary implications are explored with respect to assessment and intervention.

Disruption of the neural response to rapid acoustic stimuli in dyslexia: evidence from functional MRI

The biological basis for developmental dyslexia remains unknown. Research has suggested that a fundamental deficit in dyslexia is the inability to process sensory input that enters the nervous system rapidly and that deficits in processing rapid acoustic information are associated with impaired reading. Functional magnetic resonance imaging (fMRI) was used to identify the brain basis of rapid acoustic processing in normal readers and to discover the status of that response in dyslexic readers. Normal readers showed left prefrontal activity in response to rapidly changing, relative to slowly changing, nonlinguistic acoustic stimuli. Dyslexic readers showed no differential left frontal response. Two dyslexic readers participated in a remediation program and showed increased activity in left prefrontal cortex after training. These fMRI results identify left prefrontal regions as normally being sensitive to rapid relative to slow acoustic stimulation, insensitive to the difference between such stimuli in dyslexic readers, and plastic enough in adulthood to develop such differential sensitivity after intensive training.

Use of temporal envelope cues by children with developmental dyslexia

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

Speech-evoked neurophysiologic responses in children with learning problems: development and behavioral correlates of perception

OBJECTIVES

To evaluate the maturational progression of speech-evoked P1/N1/N2 cortical responses over the life span, determine whether responses are distinctive in clinical populations experiencing learning problems and elucidate the functional significance of these responses.

DESIGN

The P1/N1/N2 complex was measured in 150 normal subjects (5 to 78 yr) and 86 subjects with learning problems (LP) (8 to 15 yr) to a synthetic CV syllable. Analyses included description and comparison of the developmental time course in both groups and evaluation of the relationship between P1/N1/N2 and children's performance on speech discrimination tasks and standardized learning measures.

RESULTS

Findings revealed significant changes in waveform morphology, latency and amplitude as a function of age. Maturational patterns in the group of children with learning problems did not differ from the normal group. P1/N1/N2 parameters were significantly correlated with standardized tests of Spelling, Auditory Processing and Listening Comprehension in the LP group. Moreover, there was a predictive relationship between Auditory Processing and N2 latency.

CONCLUSIONS

The P1/N1/N2 complex changes throughout life from school-age to old age. The developmental sequence throughout the school-age years is similar in normal and LP children. Thus, differences in the rate of P1/Nl/N2 latency and amplitude development do not appear to be distinctive in these two populations. The relationship between P1/N1/N2 parameters and standardized measures of learning (particularly between Auditory Processing and N2 latency) provides new information about the role of these responses in hearing and highlights the potential value in characterizing auditory processing deficits.

Identification reaction times of voiced/voiceless continua: a right-ear advantage for VOT values near the phonetic boundary

We explored the degree to which the duration of acoustic cues contributes to the respective involvement of the two hemispheres in the perception of speech. To this end, we recorded the reaction time needed to identify monaurally presented natural French plosives with varying VOT values. The results show that a right-ear advantage is significant only when the phonetic boundary is close to the release burst, i.e., when the identification of the two successive acoustical events (the onset of voicing and the release from closure) needed to perceive a phoneme as voiced or voiceless requires rapid information processing. These results are consistent with the recent hypothesis that the left hemisphere is superior in the processing of rapidly changing acoustical information.

A new view of language acquisition

At the forefront of debates on language are new data demonstrating infants' early acquisition of information about their native language. The data show that infants perceptually "map" critical aspects of ambient language in the first year of life before they can speak. Statistical properties of speech are picked up through exposure to ambient language. Moreover, linguistic experience alters infants' perception of speech, warping perception in the service of language. Infants' strategies are unexpected and unpredicted by historical views. A new theoretical position has emerged, and six postulates of this position are described.

Nonlinguistic perceptual deficits associated with reading and language disorders

Recent behavioral evidence supports the idea that some individuals with reading and language disorders are impaired in their perception of nonlinguistic auditory and visual information. More sophisticated measurement paradigms and analysis techniques are leading to a clearer understanding of these deficits and to possibilities for their remediation.

Auditory temporal processing: responses to sinusoidally amplitude-modulated tones in the inferior colliculus

Time-varying envelopes are a common feature of acoustic communication signals like human speech and induce a variety of percepts in human listeners. We studied the responses of 109 single neurons in the inferior colliculus (IC) of the anesthetized Mongolian gerbil to contralaterally presented sinusoidally amplitude-modulated (SAM) tones with a wide range of parameters. Modulation transfer functions (MTFs) based on average spike rate (rMTFs) showed regions of enhancement and suppression, where spike rates increased or decreased respectively as stimulus modulation depth increased. Specifically, almost all IC rMTFs could be described by some combination of a primary and a secondary region of enhancement and an intervening region of suppression, with these regions present to varying degrees in individual rMTFs. rMTF characteristics of most neurons were dependent on sound pressure level (SPL). rMTFs in most neurons with "onset" or "onset-sustained" peri-stimulus time histograms (PSTHs) in response to brief pure tones showed only a peaked primary region of enhancement. The region of suppression tended to occur in neurons with "sustained" or "pauser" PSTHs, and usually emerged at higher SPLs. The secondary region of enhancement was only found in eight neurons. The lowest modulation frequency at which the spike rate reached a clear peak ("best modulation frequency" or BMF) was measured. All but two mean BMFs lay between 0 and 100 Hz. Fifty percent of the 49 neurons tested over at least a 20-dB range of SPLs showed a BMF variation larger than 66% of their mean BMF. MTFs based on vector strength (tMTFs) showed a variety of patterns; although mostly similar to those reported from the cochlear nucleus, tMTFs of IC neurons showed higher maximum values, smaller dynamic range with depth, and a lower high-frequency limit for significant phase locking. Systematic and large increases in phase-lead commonly occurred as SPL increased. rMTFs measured at multiple carrier frequencies (F(c)s) showed that the suppressive region was not the result of sideband inhibition. There was no systematic relationship between BMF and F(c) of stimulation in the cells studied, even at low carrier frequencies. The results suggest various possible mechanisms that could create IC MTFs, and strongly support the idea that inhibitory inputs shape the rMTF by sharpening regions of enhancement and creating a suppressive region. The paucity of BMFs above 100 Hz argues against simple rate-coding schemes for pitch. Finally, any labeled line or topographic representation of modulation frequency is unlikely to be independent of SPL.

Injury- and use-related plasticity in the adult auditory system

After restricted cochlear lesions in adult animals, the frequency selectivity of neurons in the cortical region deprived of its normal input by the lesion is changed such that the region is occupied by expanded representations of adjacent (perilesion) frequencies. Analogous changes in cortical frequency selectivity and organization are seen as a consequence of behavioral training that enhances the significance of particular acoustic stimuli. The occurrence of such reorganization in a wide range of species (including simian primates) suggests that it would also occur in humans. Direct evidence in support of this suggestion is provided by a small body of functional imaging evidence. Although such reorganization almost certainly does not have a compensatory function, such a profound change in the pattern of cortical activation produced by stimuli exciting perilesion parts of the receptor epithelium would be expected to have perceptual consequences and, perhaps, clinical implications.

Naming-speed processes, timing, and reading: a conceptual review

This article integrates the findings in the special issue with a comprehensive review of the evidence for seven central questions about the role of naming-speed deficits in developmental reading disabilities. Cross-sectional, longitudinal, and cross-linguistic research on naming-speed processes, timing processes, and reading is presented. An evolving model of visual naming illustrates areas of difference and areas of overlap between naming speed and phonology in their underlying requirements. Work in the cognitive neurosciences is used to explore two nonexclusive hypotheses about the putative links between naming speed and reading processes and about the sources of disruption that may cause subtypes of reading disabilities predicted by the double-deficit hypothesis. Finally, the implications of the work in this special issue for diagnosis and intervention are elaborated.

Auditory processing parallels reading abilities in adults

A broad battery of psychoacoustic measures and standard measures of reading and spelling were applied to 102 adults. The test group included individuals with a childhood history of reading difficulties and controls with no reported reading difficulties. Reading scores were variable in both groups. Poor auditory processing abilities were recorded in poor readers; particular difficulties were posed by tasks requiring spectral distinctions, the simplest of which was pure tone frequency discrimination. In absolute terms, the greatest deficits were recorded in tasks in which stimuli were presented in brief forms and in rapid succession. Auditory processing abilities accounted for more than 50% of the reading score variance in the control group, but their correlation with reading scores was lower in the group with childhood histories of reading difficulties. The additional variability in the latter group resulted largely from the prevalence of reading-compensated poor psychoacoustic performers, whose short-term word memory was also typically poor. Taken together, these findings support a link between impaired auditory resolution and poor reading. Psychoacoustic difficulties are largely retained through adulthood and may be the source of the retained reading difficulties.

Predicting dyslexia at 8 years of age using neonatal brain responses

Auditory event-related potentials recorded at birth to speech and nonspeech syllables from six scalp electrodes discriminated between newborn infants who 8 years later would be characterized as dyslexic, poor, or normal readers. These findings indicate that reading problems can be identified and possible interventions undertaken up to 9 years earlier than is currently possible.

Lexical word formation in children with grammatical SLI: a grammar-specific versus an input-processing deficit?

An ongoing controversy is whether an input-processing deficit or a grammar-specific deficit causes specific language impairment (SLI) in children. Previous studies have focussed on SLI childrens' omission of inflectional morphemes or impaired performance on language tasks, but such data can be accounted for by either theory. To distinguish between these theories we study compound formation in a subgroup of SLI children with 'grammatical (G)-SLI'. An input-processing account (e.g. Leonard, L. (1998). Children with specific language impairment. Cambridge, MA: MIT Press), in which perception and production of inflections requires extra processing resources, would predict that G-SLI children will omit the regular plural -s in compounds (e.g. rat-eater). A grammar-specific deficit account (e.g. Ullman, M. & Gopnik, M. (1994) The production of inflectional morphology in hereditary specific language impairment. The McGill Working Papers in Linguistics, 10, 81-118; van der Lely, H. K. J. & Ullman, M. (1996). The computation and representation of past-tense morphology in normally developing and specifically language impaired children. In A. Stringfellow, D. Cahana-Amitay, E. Hughes & A. Zukowski, Proceedings of the 20th Annual Boston University Conference on Language Development (pp. 816-827). Somerville, MA: Cascadilla Press), in which G-SLI children are impaired in regular inflectional morphology, would predict that G-SLI children will produce regular plural -s forms inside compounds (e.g. *rats-eater). We compared the responses of 16 G-SLI subjects (aged 10 years 4 months to 18 years) with those of 36 normally developing control children (24 matched on language ability and 12 matched on age and cognitive ability). All the groups produced irregular plural nouns in compounds (mice-eater). The normally developing children and teenagers rarely, if ever. produced regular plural nouns inside compounds (*rats-eater), whereas the G-SLI subjects did so often. This pattern of results conflicts with the predictions ofthe input-processing deficit account. The findings support the grammar-specific deficit hypothesis. The data rovide further evidence that specialized grammatical abilities may be differentially impaired within the language system.

Does It Matter What Your Client Thinks? The Role of Theory in Intervention

Kamhi (2000) presents a case study of a child with a phonological impairment whose view of the intervention process led her to refuse to work on her goals with anyone other than her clinician. In this response, the potential clinical impact of discrepant views among the participants in a clinical intervention is discussed. In particular, it is argued that subjectivity is inherent in all interactions, but that different theories place differing emphasis on the importance of the subjective states of interactional participants. Three prominent theories of intervention are discussed: social interactionist, behaviorist, and information processing. It is argued that discrepancies between a clinician's and a client's view of what is happening during clinical interactions may complicate intervention. It is further argued that theoretical eclecticism may have a particularly negative impact, as it will increase the likelihood of misunderstandings. A conclusion is that, when clashes in perspectives arise, they force the clinician to make explicit what he or she believes—what causes disorders, what processes work to remediate them, and why.