The effect of picture priming on event-related potentials of normal and disabled readers during a word recognition memory task

Semantic Priming and Its Link to Verbal Comprehension and Working Memory in Children with Learning Disorders

Children with learning disorders (LD children) often have heterogeneous cognitive impairments that affect their ability to learn and use basic academic skills. A proposed cause for this variability has been working memory (WM) capacity. Altered patterns of event-related potentials (ERPs) in these children have also been found in the N400 component associated with semantic priming. However, regarding the semantic priming effect in LD children, no distinction has been made for children with varying WM abilities. This study aims to explore the relationship of WM with the brain's electrophysiological response that underlies semantic priming in LD children that performed a lexical decision task. A total of 40 children (8-10 years old) participated: 28 children with LD and 12 age-matched controls. The ERPs were recorded for each group and analyzed with permutation-based t-tests. The N400 effect was observed only in the control group, and both groups showed a late positive complex (LPC). Permutation-based regression analyses were performed for the results from the LD group using the WISC-IV indices (e.g., Verbal Comprehension and WM) as independent predictors of the ERPs. The Verbal Comprehension Index, but not the WM index, was a significant predictor of the N400 and LPC effects in LD children.

Psychosocial Dimensions of Learning Disability Subtypes

Evidence bearing upon the relationships between profiles of neuropsychological assets and deficits, subtypes of learning disabilities, and patterns and degrees of psychosocial functioning is reviewed. The dimensions of incidence and type of psychosocial disturbance and the differential manifestations of these in two subtypes of learning disabilities are examined. Conclusions relating to the neurodevelopmental bases of the pattern of psychosocial functioning most often seen in children and adolescents with the syndrome of nonverbal learning disabilities are emphasized.

A review of recent literature employing electroencephalographic techniques to study the pathophysiology, phenomenology, and treatment response of schizophrenia

Clinical experience and research findings suggest that schizophrenia is a disorder comprised of multiple genetic and neurophysiological subtypes with differential response to treatment. Electroencephalography (EEG) is a non-invasive, inexpensive and useful tool for investigating the neurobiology of schizophrenia and its subtypes. EEG studies elucidate the neurophysiological mechanisms potentially underlying clinical symptomatology. In this review article recent advances in applying EEG to study pathophysiology, phenomenology, and treatment response in schizophrenia are discussed. Investigative strategies employed include: analyzing quantitative EEG (QEEG) spectral power during the resting state and cognitive tasks; applying machine learning methods to identify QEEG indicators of diagnosis and treatment response; and using the event-related brain potential (ERP) technique to characterize the neurocognitive processes underlying clinical symptoms. Studies attempting to validate potential EEG biomarkers of schizophrenia and its symptoms, which could be useful in assessing familial risk and treatment response, are also reviewed.

Association of abnormal semantic processing with delusion-like ideation in frequent cannabis users: an electrophysiological study

RATIONALE

Frequent cannabis use is a risk marker for schizophrenia and delusions, but the neurocognitive mechanisms of this relationship remain unclear.

OBJECTIVES

We sought evidence that cannabis users have deficits in processing relationships between meaningful stimuli, similar to abnormalities reported in schizophrenia, and that these deficits are associated with delusion-like ideation. We used the N400 event-related brain potential (ERP) waveform as a neurophysiological probe of activation of concepts in semantic memory. We hypothesized that cannabis users would exhibit larger (more negative) than normal N400 amplitudes in response to stimuli meaningfully related to a preceding prime-reflecting deficient activation of concepts related to the prime. We further hypothesized that the magnitude of this abnormality would correlate with severity of delusion-like ideation.

METHODS

We recorded ERPs in 24 frequent cannabis users and 24 non-using comparison participants who viewed prime words followed by targets which were either words related or unrelated to the prime or pronounceable nonwords. The participants' task was to indicate whether the target was a word. Delusion-like ideation was measured via the Schizotypal Personality Questionnaire.

RESULTS

Contrary to our hypothesis, cannabis users exhibited smaller than normal N400s to both related and unrelated targets. These abnormalities correlated with delusion-like ideation in cannabis users only.

CONCLUSIONS

The results are consistent with a generalized abnormality of activation within semantic memory neural networks in cannabis users. Further research is needed to investigate whether such an abnormality plays a role in the development of delusion-like ideation in cannabis users.

The relation between space and math: developmental and educational implications

There is a well-known relation between spatial ability and mathematics dating back to the work of early twentieth century factor analysts. This connection is a ripe opportunity for educators, who might use spatial training to improve math learning. However, a closer look at the literature reveals gaps that impede direct application. The primary problem is that although this relation is well established in older children and adults, its emergence in early development and subsequent developmental interactions are not well documented. Moreover, there is a need for more mechanistic explanations that might be leveraged to improve math education. In this chapter, we attempt to address these issues by reviewing the existing literature to identify instances where answers are available and others where further research is needed.

Atypical neural responses to phonological detail in children with developmental language impairments

Specific Language Impairment (SLI) is a developmental disorder affecting language learning across a number of domains. These difficulties are thought to be related to difficulties processing auditory speech, given findings of imperfect auditory processing across nonspeech tones, individual speech sounds and syllables. However the relationship of auditory difficulties to language development remains unclear. Perceiving connected speech involves resolving coarticulation, the imperceptible blending of speech movements across adjacent sounds, which gives rise to subtle variations in speech sounds. The present study used event-related potentials (ERPs) to examine neural responses to coarticulation in school age children with and without SLI. Atypical neural responses were observed for the SLI group in ERP indices of prelexical-phonological but not lexical stages of processing. Specifically, incongruent coarticulatory information resulted in a modulation of the N100 in the SLI but not typically developing group while a Phonological Mapping Negativity was elicited in the typically developing but not SLI group, unless additional cues were present. Neural responses to unexpected lexical mismatches indexed by the N400 ERP component were the same for both groups. The results demonstrate a relative insensitivity to important subphonemic features in SLI.

An event-related brain potential study of schizotypal personality and associative semantic processing

To examine whether schizotypal personality is associated with the degree to which concepts activate each other in semantic memory, event-related brain potentials (ERPs) were recorded during a delayed lexical decision task from healthy volunteers rated for schizotypy. Each target word was directly, indirectly, or not at all related to a prime word preceding it at a 300- or 750-ms stimulus-onset asynchrony (SOA). Overall, N400 amplitudes were largest for unrelated targets, smallest for directly related targets, and intermediate for indirectly related targets. Higher total Schizotypal Personality Questionnaire (SPQ) scores correlated with smaller N400 indirect priming effects (i.e., smaller N400 amplitude differences between unrelated and indirectly related targets) at both SOAs. In addition, schizotypal subscale scores were differentially associated with N400 effects. Higher SPQ Cognitive-Perceptual scores correlated with smaller N400 direct priming effects (smaller N400 amplitude differences between unrelated and directly related targets) at both SOAs, and with smaller N400 indirect priming effects at the shorter SOA. These correlations are consistent with the hypothesis that decreased use of meaningful context to activate related concepts in general, and/or to inhibit unrelated concepts, may play some role in the development of unusual beliefs.

Event-related potentials in clinical research: guidelines for eliciting, recording, and quantifying mismatch negativity, P300, and N400

This paper describes recommended methods for the use of event-related brain potentials (ERPs) in clinical research and reviews applications to a variety of psychiatric and neurological disorders. Techniques are presented for eliciting, recording, and quantifying three major cognitive components with confirmed clinical utility: mismatch negativity (MMN), P300, and N400. Also highlighted are applications of each of the components as methods of investigating central nervous system pathology. The guidelines are intended to assist investigators who use ERPs in clinical research, in an effort to provide clear and concise recommendations and thereby to standardize methodology and facilitate comparability of data across laboratories.

Neural correlates of age-related reduction in visual motion priming

Previously we reported that priming of visual motion perception is reduced in older adults compared to younger adults (Jiang, Greenwood, & Parasuraman, 1999, Psychology and Aging, 14(4), 619; Jiang, Luo, & Parasuraman, 2002b, Neuropsychology, 16(2), 140). To examine the neural mechanisms underlying this age-related effect, event-related brain potentials (ERPs) were recorded during perceptual judgments of motion directions by younger and older adults in two experiments. When judging single-step motion, both younger and older adults evoked significantly larger ERP late positive component (LPC) responses to unambiguous motion compared to LPC responses elicited by ambiguous motion. In contrast, compared to the younger adults, the older adults evoked comparable but delayed ERP responses to single motion steps. In the second experiment the younger and older groups judged the directions of two successive motion-steps (either motion priming or motion reversals). Under short (200-400 ms) stimulus onset asynchrony (SOA), the difference between the ERP responses to priming and reversal conditions was significantly larger for the younger than for the older adults. This study provides the first electrophysiological evidence that brain aging leads to delayed processing of single motion direction and visual motion priming as early as 100 ms in the early visual cortex. Age-related changes in strength and temporal characteristics of neural responses in temporal-parietal regions were particularly pronounced in older adults when successive motion signals are placed closely in time, within 400 ms.

Semantic, syntactic, and phonological processing of written words in adult developmental dyslexic readers: an event-related brain potential study

Background

The present study used event-related brain potentials to investigate semantic, phonological and syntactic processes in adult German dyslexic and normal readers in a word reading task. Pairs of German words were presented one word at a time. Subjects had to perform a semantic judgment task (house – window; are they semantically related?), a rhyme judgment task (house – mouse; do they rhyme?) and a gender judgment task (das – Haus [the – house]; is the gender correct? [in German, house has a neutral gender: das Haus]).

Results

Normal readers responded faster compared to dyslexic readers in all three tasks. Onset latencies of the N400 component were delayed in dyslexic readers in the rhyme judgment and in the gender judgment task, but not in the semantic judgment task. N400 and the anterior negativity peak amplitudes did not differ between the two groups. However, the N400 persisted longer in the dyslexic group in the rhyme judgment and in the semantic judgment tasks.

Conclusion

These findings indicate that dyslexics are phonologically impaired (delayed N400 in the rhyme judgment task) but that they also have difficulties in other, non-phonological aspects of reading (longer response times, longer persistence of the N400). Specifically, semantic and syntactic integration seem to require more effort for dyslexic readers and take longer irrespective of the reading task that has to be performed.

Electrophysiological insights into conceptual disorganization in schizophrenia

Disorganized speech, or thought disorder, in schizophrenia may reflect abnormal processing of meaningful concepts. To examine whether schizophrenia involves abnormalities in how a meaningful context influences processing of concepts strongly, weakly, or not related to it, we used the N400, an event-related brain potential (ERP) index of semantic relatedness. ERPs were recorded from schizophrenia patients (n=18) and normal controls (n=18) while they viewed category definitions (e.g., a type of fruit), each followed by a target word that was either a high-typicality category exemplar (apple), low-typicality exemplar (cherry), or non-exemplar (clamp). Participants' task was to indicate via button-press whether or not the target belonged to the category. In both patients and controls, N400 amplitude was largest (most negative) for non-exemplars, intermediate for low-typicality exemplars, and smallest (least negative) for high-typicality exemplars. Compared to controls, patients showed a trend toward reduced N400 amplitude differences between non-exemplars and low-typicality exemplars. Most importantly, within patients, reduced N400 amplitude differences between high- and low-typicality exemplars were correlated with psychotic symptoms. This association of an N400 index of semantic processing with psychotic symptoms suggests that psychosis in schizophrenia may be associated with greater similarity in how concepts strongly and weakly meaningfully related to their context are processed.

Association of schizotypy with semantic processing differences: an event-related brain potential study

Disorganized speech in both schizophrenia and schizotypy has been hypothesized to result from abnormalities in how concepts activate one another in semantic memory. To study whether schizotypy is associated with differences in how categories activate their exemplars, we examined the N400 component of the event-related brain potential (ERP) elicited during a category-verification task. ERPs were recorded in young adults from the general population while they viewed category definitions each followed by a target that was either a high-typicality exemplar, low-typicality exemplar, or non-exemplar; participants' task was to indicate whether or not the target belonged to the category. Schizotypy was assessed via the Schizotypal Personality Questionnaire (SPQ). Overall, N400 amplitude was largest for non-exemplars, smallest for high-typicality exemplars, and intermediate for low-typicality exemplars. SPQ score was associated with decreased N400 amplitude to non-exemplars, and increased amplitude to both types of exemplars. SPQ score was negatively correlated with the N400 amplitude difference between non-exemplars and both low- and high-typicality exemplars, but was not correlated with the amplitude difference between low- and high-typicality exemplars. N400 amplitude differences between non-exemplars and both types of exemplars were correlated with the SPQ Interpersonal factor, but not the Disorganized factor. The results are consistent with an association of schizotypy with decreased use of context to activate related items and inhibit unrelated items.

Language disorder in schizophrenia as a developmental learning disorder

Receptive language disorder in schizophrenia is hypothesized to represent a learning disorder that involves a neurodevelopmental etiology. It is argued that a preexisting developmental language disorder may characterize a subset of schizophrenia patients. A primary deficit in the temporal dynamics of brain function is assumed to cause receptive language disorder in schizophrenia. This hypothesized core deficit includes both disturbance in the processing of rapid, sequential information and disruptions to patterns of brain activation and synchronization. These timing deficits may alter the way associative connections are formed and/or accessed in semantic memory. It is suggested that abnormalities in second-messenger pathways of subcortical-cortical circuitry offer an etiological nexus for language dysfunction in schizophrenia and developmental dyslexia.

Learning disability subtypes and the role of attention during the naming of pictures and words: an event-related potential analysis

The role of attention in the processing of pictures and words was investigated for a group of normally achieving children and for groups of learning disability sub-types that were defined by deficient performance on tests of reading and spelling (Group RS) and of arithmetic (Group A). An event-related potential (ERP) recording paradigm was employed in which the children were required to attend to and name either pictures or words that were presented individually or in superimposed picture-word arrays that varied in degree of semantic relation. For Group RS, the ERP waves to words, both presented individually or attended in the superimposed array, exhibited reduced N450 amplitude relative to controls, whereas their ERP waves to pictures were normal. This suggests that the word-naming deficiency for Group RS is not a selective attention deficit but rather a specific linguistic deficit that develops at a later stage of processing. In contrast to Group RS and controls, Group A did not exhibit reliable early frontal negative waves (N280) to the super-imposed pictures and words, an effect that may reflect a selective attention deficit for these children that develops at an early stage of visuo-spatial processing. These early processing differences were also evident in smaller amplitude N450 waves for Group A when naming either pictures or words in the superimposed arrays.

Recognition memory for unfamiliar faces does not differ for adult normal and dyslexic readers: an event-related brain potential study

OBJECTIVE

Differences in recognition memory for unfamiliar faces between adult developmental dyslexic (n=12) and normal readers (n=12) were studied by means of event-related brain potentials.

METHODS

Subjects performed a continuous face recognition task, in which 240 unfamiliar faces were presented on a computer screen, 100 of which were repetitions. For each face, subjects had to indicate whether it was presented before or not. Performance did not differ between normal and dyslexic readers. Old/repeated faces elicited more positive event-related potentials (ERPs) starting 250 ms poststimulus. These were analyzed in two time-windows encompassing the early (250-450 ms) and the late phase (450-750 ms) of the old/new effect.

RESULTS

No group difference in amplitude or topography of the old/new effect emerged. However, ERPs for all faces were more positive for normal compared with those of dyslexic readers.

CONCLUSIONS

These results show that a previously described recognition memory deficit for words in dyslexic readers is likely to be specific for verbal material.

Developmental dyslexics show altered allocation of attention in visual classification tasks

OBJECTIVES

Event-related brain potentials (ERPs) were recorded to investigate allocation of attention in adult developmental dyslexics.

SUBJECTS AND METHODS

Twelve adult developmental dyslexics and 12 matched normal controls performed three visual choice reaction tasks. In the passive oddball condition, subjects watched two different simple visual stimuli presented with 87.5 and 12.5% probability. In the active oddball condition, participants responded to the low-probability target stimulus. In the active 50/50-condition, both stimuli were presented with 50% probability and a response was required to the target stimulus only.

RESULTS

No group differences emerged for performance, P300 latency or laterality and for N200 amplitude, latency or laterality. An enhancement of P300 amplitude with a frontal distribution was found for NoGo (standard)-stimuli in both active conditions for the dyslexic sample.

CONCLUSION

Results are discussed in the context of deviances in allocation of attentional resources in dyslexic readers.

Event-related potentials and picture-word naming: effects of attention and semantic relation for children and adults

Event-related potentials (ERPs) were recorded from children, 9 to 13 years of age, while they named words and pictures. The words and pictures were presented individually and in superimposed picture-word pairs in which the meaning of the words and pictures was either congruent, semantically associated, or incongruent. Both words and pictures elicited large amplitude negative waves (N450) at anterior electrode sites. The amplitude of this N450 wave was larger for individually presented pictures than for words. N450 amplitude was also larger when naming pictures than when naming words in the superimposed arrays, an effect that is attributed to differences in attentional demand required to name pictures rather than to exogenous stimulus characteristics. No significant effects of semantic incongruity were observed. These ERP waveforms for children differ from those observed for adults who exhibited positive amplitude waves to individually presented pictures and who also exhibited semantic incongruity effects.

An electrophysiological study of dyslexic and control adults in a sentence reading task

Event-related potentials and cued-recall performance were used to compare dyslexic and control adult subjects. Sentences that ended either congruously or incongruously were presented visually, one word at a time, at fast (stimulus-onset-asynchrony (SOA)=100 ms) or slow (SOA=700 ms) rates of presentation. Results revealed (1) a large effect of presentation rate that started with the N1-P2 components and lasted for the entire recording period, (2) larger N400 components for dyslexic than control subjects, at slow presentation rates, to both congruous and incongruous endings and (3) a large ERPs difference related to memory (Dm effect) that did not differentiate controls from dyslexics but was larger at slow than at fast rates of presentation. These findings indicate that the reading impairment observed in the present group of adult dyslexics is more likely to result from difficulties integrating the meaning of words within a sentence context than from pure sensory processing deficits.

Electrophysiological dissociation between verbal and nonverbal semantic processing in learning disabled adults

Event-related potentials (ERPs) were recorded as 16 adults with learning disabilities (LD) and 16 controls were presented with two sets of stimuli. The first set comprised pairs of line drawings and environmental sounds (nonverbal condition); the second consisted of printed and spoken words (verbal condition). In the controls, semantically related items elicited smaller N400s than unrelated items in both conditions, with opposing hemispheric asymmetries for spoken words and environmental sounds. The LD group did not show a significant difference between related and unrelated words, despite a robust context effect for nonspeech sounds. The results suggest anomalous processing limited to the verbal domain in a simple semantic association task in the LD group. Semantic deficits in this group may reflect a relatively specific deficit in forming verbal associations rather than a more general difficulty that spans both verbal and nonverbal domains.

The relation of ERP components to complex memory processing

The relation between various ERP components generated during encoding of a word and its subsequent recall were investigated using a "rote" serial-order and an "elaborative" category memory task. Words (flashed separately) were time-locked to EEG recordings from 21 cortical sites. ERP components from the five subjects having the highest recall scores were compared to the five lowest scoring subjects. Results based on the P200 peak amplitude data as well as the N400 and late positive component peak amplitude and latency data suggest that anterior and posterior distributional differences are elicited during encoding of words for rote and elaborative memory tasks. Furthermore, strong individual differences in these patterns were found as a function of task. A tentative argument was made that the obtained anterior and posterior differences may index different word feature selection and encoding processes, which are differentially utilized by high and low recallers.

Auditory ERPs during rhyme and semantic processing: effects of reading ability in college students

Event-related potential (ERP), reaction time (RT), and response accuracy measures were obtained during the phonological and semantic categorization of spoken words in 14 undergraduates: 7 were average readers and 7 were reading-impaired. For the impaired readers, motor responses were significantly slower and less accurate than were those of the average readers in both classification tasks. ERPs obtained during rhyme processing displayed a relatively larger amplitude negativity at about 480 ms for the impaired readers as compared to the average readers, whereas semantic processing resulted in no major group differences in the ERPs at this latency. Also, N480 amplitude was larger during semantic relative to phonological classification for the average readers but not for the impaired readers. Results are compared to a previous study of reading-impaired children on the same tasks.

Late cognitive brain potentials, phonological and semantic classification of spoken words, and reading ability in children

Event-related potential (ERP), reaction time, and response accuracy measures were obtained during rhyming and semantic classification of spoken words in 10 average (mean age 11.64 years) and 9 impaired reading (mean age 12.10 years) children. The behavioral measures of classification did not distinguish the groups. In the ERPs, rhyme processing produced more pronounced group differences than did semantic processing at about 480 ms, with a relatively more negative distribution for the impaired readers at centroparietal sites. At about 800 ms in both classification tasks, the impaired readers displayed a late positivity that was delayed in latency and of larger amplitude at frontal sites than that for the average readers. The ERP findings suggest that the categorization of spoken words for meaning and sound result in increasingly more aberrant correlates of these processing demands in reading-impaired children.

Event-related brain potentials elicited by rhyming and non-rhyming pictures differentiate subgroups of reading disabled adolescents

Event-related brain potentials were recorded while disabled adolescent subjects read and judged whether two sequentially presented pictures had names that rhymed. Subjects with relatively good phonetic skills displayed an N400 priming effect, i.e., a significant reduction in the amplitude of the negative peak, occurring approximately 400 msec post-stimulus, for pictures with names that rhymed with preceding pictures as compared with pictures that had names that did not rhyme with the prime. No such effect was evident for subjects with relatively poor phonetic skills. This lack of an N400 priming effect provides evidence for a reduction in neural capacity and/or activation during phonological processing in the subjects with poor phonological skills. Demonstrating the N400 priming effect to be stronger in one group of reading disabled subjects, compared to another, supports the position that specific subtypes of reading disability exist. In addition to the stronger N400 priming effect, the phonetically stronger group also exhibited an enhanced negativity, from 700 to 1,000 msec after target stimulus onset, compared to phonetically inferior subjects. This finding replicates earlier work and possibly reflects a higher level of confidence in the group with better phonetic skills.

Brain potentials in developmental dyslexia: differential effects of word frequency in human subjects

The differences of word processing between a group of adult developmental dyslexics and control subjects were examined with the event-related potential (ERP) technique. In particular, the effects of word frequency and word recognition were assessed. The subjects viewed a series of frequently and infrequently used words, most of which were repeated after some intervening items and they discriminated between first and second presentations of the words. It can be shown that in the range from 300 to 550 ms post stimulus the amplitude of the N400 component, an ERP measure of semantic processing, is reduced for high frequency words. This effect is more pronounced in the dyslexic group and the effects of word recognition are also reduced in the dyslexic group for high frequency words. These findings are discussed with respect to current concepts of dyslexia and of semantic processing.

Assessing adult receptive vocabulary with event-related potentials: an investigation of cross-modal and cross-form priming

This experiment investigated whether a relationship existed between event-related potentials (ERPs) and performance on a standardized measure of receptive vocabulary; a computer adapted version of the Peabody Picture Vocabulary Test-Revised (PPVT-R); using Preschooler, Child, and Adult levels of difficulty. Pictures (N = 90) were presented twice, once paired with a congruent spoken word and again paired with an incongruent word. Two ERP components (PMN and N400) were clearly and reliably larger in response to incongruent than congruent picture/spoken-word pairs. Importantly, ERP differentiation of congruent and incongruent pairs occurred only at vocabulary levels at or below the subjects' psychometrically determined vocabulary range. ERP differentiation did not occur at the highest level of vocabulary where subjects experienced more uncertainty and made more behavioral errors. These results are discussed in relation to the use of ERP measures in the assessment of receptive vocabulary levels.

An innovative method to assess the receptive vocabulary of children with cerebral palsy using event-related brain potentials

This single-case, multiple-control study illustrates the clinical use of ERPs as part of the linguistic and cognitive assessment of individuals who are unable to provide verbal or motor responses due to their multiple handicaps. The single-word receptive vocabulary of a 17-year-old patient with Cerebral Palsy (CP) and three age-matched controls was measured using an event-related potential (ERP) paradigm. The Peabody Picture Vocabulary Test-Revised (PPVT-R) was adapted for computer presentation, with three levels of difficulty (Preschool, Child, Adult). Individual pictures were presented successively, and correctly (congruent) or incorrectly (incongruent) named auditorially. ERP components were derived for both the congruent and incongruent picture-word pairs. As predicted, the N400 ERP component had a higher peak for the incongruent picture-word pairs at the Preschool and Child levels. At the Adult level, the ERP pattern was reversed (higher peak in congruent condition) for the CP patient and for two of the three controls and, it was substantially attenuated for the third control. These ERP findings indicated that picture-word pairs within the range of acquired receptive vocabulary were identified as correct or incorrect but picture-word pairs above an individual's level could not be differentiated as clearly. The findings demonstrate the clinical application of this paradigm to assessing receptive vocabulary in motor- and communication-impaired patients.

Developmental dyslexia and animal studies: at the interface between cognition and neurology

Recent findings in autopsy studies, neuroimaging, and neurophysiology indicate that dyslexia is accompanied by fundamental changes in brain anatomy and physiology, involving several anatomical and physiological stages in the processing stream, which can be attributed to anomalous prenatal and immediately postnatal brain development. Epidemiological evidence in dyslexic families led to the discovery of animal models with immune disease, comparable anatomical changes and learning disorders, which have added needed detail about mechanisms of injury and plasticity to indicate that substantial changes in neural networks concerned with perception and cognition are present. It is suggested that the disorder of language, which is the cardinal finding in dyslexic subjects, results from early perceptual anomalies that interfere with the establishment of normal cognitive-linguistic structures, coupled with primarily disordered cognitive processing associated with developmental anomalies of cortical structure and brain asymmetry. This notion is supported by electrophysiological data and by findings of anatomical involvement in subcortical structures close to the input as well as cortical structures involved in language and other cognitive functions. It is not possible at present to determine where the initial insult lies, whether near the input or in high-order cortex, or at both sites simultaneously.

Visual event-related potentials of dyslexic children to rhyming and nonrhyming stimuli

In a visual event-related potential (ERP) study, children diagnosed as dyslexic in terms of both age and IQ discrepancy criteria were compared with two contrast groups: poor for age (SLOW) readers and normal reading children with Attention Deficit Disorder (ADD). The children viewed 200 stimulus pairs and judged whether the second stimulus of each pair rhymed with the first. The first stimulus was always a three-letter word, while half of the second stimuli were pronounceable nonsense words and half were real words. Rhyme probability was 50%. The ERP waveforms of the dyslexics were significantly different from those of the ADD group in showing less late negativity. The SLOW group's waveforms more closely paralleled those of the ADD group. The major anomalous feature of the dyslexics' waveform was a pronounced late positive peak (P500), which followed an attenuated N450 peak. Over all groups, the N450 peak was sensitive to the rhyme manipulation, as has been found in adults (Rugg, 1984a, 1984b). Real words and nonsense words produced similar waveforms. Hemispheric effects were found but did not interact with group. Results suggest non-automatic visual cognitive processing of rhyme in dyslexics.

Arithmetic disabilities, specific and otherwise: a neuropsychological perspective

From a neuropsychological perspective, this article summarizes research that addresses some of the developmental interactions of disabilities in reading, spelling, and mechanical arithmetic. The focus is on two subtypes of children with learning disabilities who exhibit equally impaired levels of arithmetic achievement, but with vastly different patterns of neuropsychological assets and deficits. Qualitative as well as quantitative analyses lead to the conclusion that one of these patterns of neuropsychological assets and deficits (i.e., the nonverbal learning disabilities syndrome; NLD) leads--at the same time and in much the same manner--to specific patterns of impairment in mechanical arithmetic and in psychosocial functioning. The other pattern (Group R-S) is found to lead to particular patterns of academic deficits (including arithmetic), but not to any particular level or type of psychosocial dysfunction. The manifestations of the NLD profile in various types of neurological disease, disorder, and dysfunction are also explored.

Electrophysiological evidence of lateralized disturbances in children with learning disabilities

This study used an electrophysiological measurement operation to investigate lateralized processing deficits associated with academic learning-disability subtypes. Fast frequency EEG activity in the 36-44 hertz (Hz) band was recorded from reading-disabled (RLD), arithmetic-disabled (ALD), and nondisabled control children engaged in verbal and nonverbal cognitive tasks. The control group, but neither LD group, exhibited a task-dependent shift in lateralization of 40 Hz EEG; the RLD subjects generated proportionately less left-hemisphere 40 Hz activity than control or ALD subjects during the verbal task; and the ALD subjects generated proportionately less right-hemisphere activity than control or RLD subjects during the nonverbal task. These results indicate that lateralized processing deficits are associated with different types of disabilities, and provide external validation of learning-disability classifications based on academic performance patterns.