From single to multiple deficit models of developmental disorders

The emerging etiological model for developmental disorders, like dyslexia, is probabilistic and multifactorial while the prevailing cognitive model has been deterministic and often focused on a single cognitive cause, such as a phonological deficit as the cause of dyslexia. So there is a potential contradiction in our explanatory frameworks for understanding developmental disorders. This paper attempts to resolve this contradiction by presenting a multiple cognitive deficit model of developmental disorders. It describes how this model evolved out of our attempts to understand two comorbidities, those between dyslexia and attention deficit hyperactivity disorder (ADHD) and between dyslexia and speech sound disorder (SSD).     

Emotion recognition in schizophrenia: further investigation of generalized versus specific deficit models

In this study, the authors examined the nature of emotion perception in schizophrenia. Two samples of people with schizophrenia, one receiving acute care for a recent exacerbation of symptoms and the other receiving extended care, were compared with a nonclinical control group on emotion perception and general perception measures. The nonclinical control group obtained the highest scores on all of the study measures, and the acutely ill group obtained the lowest scores. Furthermore, the acutely ill sample had a specific deficit in emotion perception that remained present after controlling for performance on the general perception tasks. Conversely, the deficits in emotion discrimination in the extended-care sample reflected generalized poor performance. Differences in performance on the emotion identification task between the 2 clinical groups were reduced when controlling for active symptoms.     

Pseudoname learning by German-speaking children with dyslexia: evidence for a phonological learning deficit

In 2 experiments, German-speaking dyslexic children (9-year-olds) showed impaired learning of new phonological forms (pseudonames) in a variety of visual-verbal learning tasks. The dyslexic deficit was also found when phonological retrieval cues were provided and when the to-be-learned pseudonames were presented in spoken as well as printed form. However, the dyslexic children showed no name-learning deficit when short, familiar words were used and they also had no difficulty with immediate repetition of the pseudowords. The dyslexic children's difficulty in learning new phonological forms was associated with pseudoword-repetition and naming-speed deficits assessed at the beginning of school, but not with phonological awareness and visual-motor impairments. We propose that the difficulty in learning new phonological forms may affect reading and spelling acquisition via impaired storage of new phonological forms, which serve as phonological underpinnings of the letter patterns of words or parts of words.     

Modeling single versus multiple systems in implicit and explicit memory

It is currently controversial whether priming on implicit tasks and discrimination on explicit recognition tests are supported by a single memory system or by multiple, independent systems. In a Psychological Review article, Berry and colleagues used mathematical modeling to address this question and provide compelling evidence against the independent-systems approach.     

Attentional modulation of visual processing in adult dyslexia: a spatial-cuing deficit

Anumber of researchers have suggested that deficient visual attention may play a causal role in dyslexia. However, traditional methods for investigating this assertion have been limited by the conflation of sensory and attentional factors and the inability to isolate large attentional effects. In this study, we sought to overcome these problems by combining spatial cuing with a visual search task measuring psychophysical thresholds. In normal readers, uncued search performance was characterized by a strong dependence on the number of elements in the stimulus array. Cuing the location of the target removed much of this effect, suggesting attentional facilitation of performance. Although dyslexic participants' performance in uncued search was nearly identical to that of normal readers, all dyslexic participants failed to gain the same effect of cuing that normal readers did. However, dyslexic participants did not differ from normal readers on tests of magnocellular function, suggesting that this spatial-cuing deficit is not merely a secondary consequence of magnocellular dysfunction.     

The brain basis of the phonological deficit in dyslexia is independent of IQ

Although the role of IQ in developmental dyslexia remains ambiguous, the dominant clinical and research approaches rely on a definition of dyslexia that requires reading skill to be significantly below the level expected given an individual's IQ. In the study reported here, we used functional MRI (fMRI) to examine whether differences in brain activation during phonological processing that are characteristic of dyslexia were similar or dissimilar in children with poor reading ability who had high IQ scores (discrepant readers) and in children with poor reading ability who had low IQ scores (nondiscrepant readers). In two independent samples including a total of 131 children, using univariate and multivariate pattern analyses, we found that discrepant and nondiscrepant poor readers exhibited similar patterns of reduced activation in brain areas such as left parietotemporal and occipitotemporal regions. These results converge with behavioral evidence indicating that, regardless of IQ, poor readers have similar kinds of reading difficulties in relation to phonological processing.     

The nature of the reading deficit in developmental dyslexia: a reply to Ellis

Ellis (1979) credits me with the view that “developmental dyslexia might be regarded as a genetic form of deep dyslexia” and then proceeds to argue that my grounds for this view are ill-founded. He offers an alternative proposal, that developmental dyslexia may be likened to (acquired) surface dyslexia. In this paper I will attempt to answer Ellis' (1979) criticisms and provide a critique of his alternative proposal.     

The fragile nature of the speech-perception deficit in dyslexia: natural vs synthetic speech

A number of studies reported that developmental dyslexics are impaired in speech perception, especially for speech signals consisting of rapid auditory transitions. These studies mostly made use of a categorical-perception task with synthetic-speech samples. In this study, we show that deficits in the perception of synthetic speech do not generalise to the perception of more naturally sounding speech, even if the same experimental paradigm is used. This contrasts with the assumption that dyslexics are impaired in the perception of rapid auditory transitions.     

Comparing intervention outcomes in smokers treated for single versus multiple behavioral risks.

This study examined treatment outcomes among smokers with single versus multiple behavioral risks. Data were drawn from smokers (N = 2,326) participating in 3 population-based, multibehavioral studies targeting cigarette smoking, high-fat diets, and high-risk sun exposure. Outcomes were compared for participants at risk for smoking only (13%), smoking plus 1 additional risk factor (37%), and smoking plus 2 additional risk factors (50%). The smoking only group tended to be female, older, more educated, lighter smokers, in the preparation stage of change for smoking, with more previous quit attempts and longer periods of abstinence. At 12 and 24 months follow-up, treatment of 1 or 2 coexisting risk factors did not decrease the effectiveness of smoking cessation treatment, and treatment for the coexisting factors was effective.     

A comparison of multiple versus single examples of the correct stimulus on task acquisition and generalization by persons with developmental disabilities

In teaching discriminations to persons with retardation, we often presume we will improve acquisition and generalization if we use multiple examples of boththe correct and incorrect stimuli. Two experiments were conducted to test this hypothesis. In the first experiment, 7 persons with moderate retardation learned to discriminate between functional words under two conditions. In one condition, Multiple Example of S- Only,1 example of the correct stimulus (S+) and 10 examples of the incorrect stimulus (S-) were used during acquisition. In the other condition, Multiple Examples of S+ and S-,10 examples of the S+ and 10 examples of the S- were used. Results showed that the condition which presented only a single example of S+ was superior 16 times and inferior 4 times during acquisition, generalization, and maintenance. A second experiment was conducted to (a) replicate the methodology and procedures in Experiment 1 with different participants, (b) determine whether the results were replicable, and (c) obtain efficiency data. Results replicated the findings of the first experiment. The condition which presented only a single example of S+ was superior on measures of (a) trials to criterion, (b) percent correct during acquisition, and (c) minutes to criterion. On measures of generalization, the two conditions were relatively equal. Thus, the condition which presented only a single example of the correct stimulus was more efficient and was just as effective in generalization as the condition which presented multiple examples of both the S+ and S-. These surprising results were discussed in terms of stimulus control, why students performed just as well during generalization when only one example of the S+ was used, why acquisition was also poorer for this condition, and how future studies might address these points.     

Interhemispheric communication involving multiple tasks: A study of children with dyslexia

The study investigated whether inefficient interhemispheric communication is involved in developmental dyslexia using multiple tasks. A finger localization task, rhyming judgment task, primed lexical decision task, and a visual half-field presentation paradigm were used. Nineteen dyslexic children (mean age = 13.1 years) were compared with 26 chronological age-matched normal children. Although the dyslexic group demonstrated significantly slower and less accurate performance in all three tasks, there was no significant group difference in term of interhemispheric communication. However, priming effects demonstrated by the dyslexic group (p < .05) further indicate that their reading problems may stem from the word retrieval process from the long term memory.     

The diagnostic value of cerebellar-vestibular tests in detecting learning disabilities, dyslexia, and attention deficit disorder

Neurological and optokinetic measures of cerebellar-vestibular (CV) dysfunctioning were shown to be of significant diagnostic value in differentiating between learning disabled subjects and controls matched for chronological age, sex, handedness, IQ, and background (ns = 35). Although traditionally used electronystagmographic positional and caloric parameters were not similarly discriminating, quantitative measures of vertical nystagmus in various eyes-closed positions appeared to have diagnostic potential and were related significantly to such CV-determined neurological signs as positive monopedal Romberg. As a substantial majority of learning disabled (82.9%) evidenced ADD-like symptoms and since learning disabled subsamples with and without Attention Deficit Disorder (ADD) shared similar coexisting symptoms and CV signs, it appeared probable that learning disabilities and ADD were reflections of the same underlying CV determinants.     

Evidence for a specific cross-modal association deficit in dyslexia: an electrophysiological study of letter-speech sound processing

The phonological deficit theory of dyslexia assumes that degraded speech sound representations might hamper the acquisition of stable letter-speech sound associations necessary for learning to read. However, there is only scarce and mainly indirect evidence for this assumed letter-speech sound association problem. The present study aimed at clarifying the nature and the role of letter-speech sound association problems in dyslexia by analysing event-related potentials (ERP) of 11-year-old dyslexic children to speech sounds in isolation or combined with letters, which were presented either simultaneously with or 200 ms before the speech sounds. Recent studies with normal readers revealed that letters systematically modulated speech sound processing in an early (mismatch negativity or MMN) and late (Late Discriminatory Negativity or LDN) time-window. The amplitude of the MMN and LDN to speech sounds was enhanced when speech sounds were presented with letters. The dyslexic readers in the present study, however, did not exhibit any early influences of letters on speech sounds even after 4 years of reading instruction, indicating no automatic integration of letters and speech sounds. Interestingly, they revealed a systematic late effect of letters on speech sound processing, probably reflecting the mere association of letters and speech sounds. This pattern is strongly divergent from that observed in age-matched normal readers, who showed both early and late effects, but reminiscent of that observed in beginner normal readers in a previous study (Froyen, Bonte, van Atteveldt & Blomert, 2009). The finding that the quality of letter-speech sound processing is directly related to reading fluency urges further research into the role of audiovisual integration in the development of reading failure in dyslexia.     

Individual differences in multiple types of shifting attention

Many researchers consider costs in shifting attention and mental set to reflect a basic ability to use top-down goal information to guide action. Although switch costs have been used as measures of individuals' executive function, whether common abilities underlie task set switching across different types of shifting tasks has not been well studied. In 249 participants, we studied whether switch costs in a novel two-choice reaction time task were correlated across variations in two variables: thelocus of representation (stimuli were either perceptually available or stored in working memory [WM]) and which of two judgment tasks was performed. Switch costs were asymmetrical, in that it was easier to switch to the easier judgment, and were related to overall and relative processing speed: Switch costs were higher when the task was more difficult. These factors should be accounted for when one is measuring individual differences in switch costs. After controlling for these effects, we found evidence for a common ability underlying switch costs that involved both task set preparation and response selection; however, residual shift costs, which involve only response selection, were uncorrelated across tasks. Correlations among switch costs were substantially higher within task type (e.g., correlations of WM shifting tasks with other WM shifting tasks and of perceptual tasks with perceptual ones), suggesting that there are also processes unique to switching within WM and switching among visible stimuli.     

Individual differences in the suppression of unwanted memories: the executive deficit hypothesis

When confronted with reminders to an unpleasant memory, people often try to prevent the unwanted memory from coming to mind. In this article, we review behavioral and neurocognitive evidence concerning the consequences of exerting such control over memory retrieval. This work indicates that suppressing retrieval is accomplished by control mechanisms that inhibit the unwanted memories, making them harder to recall later, even when desired. This process engages executive control mechanisms mediated by the lateral prefrontal cortex to terminate recollection-related activity in the hippocampus. Together, these findings specify a neurocognitive model of how memory control operates, suggesting that executive control may be an important means of down-regulating intrusive memories over time. We conclude by proposing that individual differences in the regulation of intrusive memories in the aftermath of trauma may be mediated by pre-existing differences in executive control ability. In support of this executive deficit hypothesis, we review the recent work indicating links between executive control ability and memory suppression.     

Individual differences in the strength of taxonomic versus thematic relations

Knowledge about word and object meanings can be organized taxonomically (fruits, mammals, etc.) on the basis of shared features or thematically (eating breakfast, taking a dog for a walk, etc.) on the basis of participation in events or scenarios. An eye-tracking study showed that both kinds of knowledge are activated during comprehension of a single spoken word, even when the listener is not required to perform any active task. The results further revealed that an individual's relative activation of taxonomic relations compared to thematic relations predicts that individual's tendency to favor taxonomic over thematic relations when asked to choose between them in a similarity judgment task. These results indicate that individuals differ in the relative strengths of their taxonomic and thematic semantic knowledge and suggest that meaning information is organized in 2 parallel, complementary semantic systems. (PsycINFO Database Record (c) 2012 APA, all rights reserved).