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).     

Conduction aphasia, sensory-motor integration, and phonological short-term memory - an aggregate analysis of lesion and fMRI data

Conduction aphasia is a language disorder characterized by frequent speech errors, impaired verbatim repetition, a deficit in phonological short-term memory, and naming difficulties in the presence of otherwise fluent and grammatical speech output. While traditional models of conduction aphasia have typically implicated white matter pathways, recent advances in lesions reconstruction methodology applied to groups of patients have implicated left temporoparietal zones. Parallel work using functional magnetic resonance imaging (fMRI) has pinpointed a region in the posterior most portion of the left planum temporale, area Spt, which is critical for phonological working memory. Here we show that the region of maximal lesion overlap in a sample of 14 patients with conduction aphasia perfectly circumscribes area Spt, as defined in an aggregate fMRI analysis of 105 subjects performing a phonological working memory task. We provide a review of the evidence supporting the idea that Spt is an interface site for the integration of sensory and vocal tract-related motor representations of complex sound sequences, such as speech and music and show how the symptoms of conduction aphasia can be explained by damage to this system.     

Which children benefit from letter names in learning letter sounds?

Typical U.S. children use their knowledge of letters' names to help learn the letters' sounds. They perform better on letter sound tests with letters that have their sounds at the beginnings of their names, such as v, than with letters that have their sounds at the ends of their names, such as m, and letters that do not have their sounds in their names, such as h. We found this same pattern among children with speech sound disorders, children with language impairments as well as speech sound disorders, and children who later developed serious reading problems. Even children who scored at chance on rhyming and sound matching tasks performed better on the letter sound task with letters such as v than with letters such as m and h. Our results suggest that a wide range of children use the names of letters to help learn the sounds and that phonological awareness, as conventionally measured, is not required in order to do so.     

Is there an alternative cerebral network associated with enhanced phonological processing in deaf speech-users? An exceptional case

Most people born deaf and exposed to oral language show scant evidence of sensitivity to the phonology of speech when processing written language. In this respect they differ from hearing people. However, occasionally, a prelingually deaf person can achieve good processing of written language in terms of phonological sensitivity and awareness, and in this respect appears exceptional. We report the pattern of event-related fMRI activation in such a deaf reader while performing a rhyme-judgment on written words with similar spelling endings that do not provide rhyme clues. The left inferior frontal gyrus pars opercularis and the left inferior parietal lobe showed greater activation for this task than for a letter-string identity matching task. This participant was special in this regard, showing significantly greater activation in these regions than a group of hearing participants with a similar level of phonological and reading skill. In addition, SR showed activation in the left mid-fusiform gyrus; a region which did not show task-specific activation in the other respondents. The pattern of activation in this exceptional deaf reader was also unique compared with three deaf readers who showed limited phonological processing. We discuss the possibility that this pattern of activation may be critical in relation to phonological decoding of the written word in good deaf readers whose phonological reading skills are indistinguishable from those of hearing readers.     

文盲与非文盲汉字字形和语音加工的脑机制

利用功能性磁共振成像(fMRI)技术探讨文盲和非文盲汉字字形和语音加工脑机制的差异。实验1使用汉字字形和图形比较了中国人文盲和非文盲字形加工过程脑机制的左侧差异。实验2使用汉字语音和纯音比较了文盲和非文盲语音加工过程脑机制的双侧差异。结果表明文盲与非文盲汉字字形和语音加工脑机制不同,且非文盲的脑活动强。     

Executive working memory processes in dyslexia: Behavioral and fMRI evidence

Beneventi, H., Tønnessen, F. E., Ersland, L. & Hugdahl, K. (2010). Executive working memory processes in dyslexia: Behavioral and fMRI evidence. Scandinavian Journal of Psychology, 51, 192–202. Dyslexia is an impairment in learning to read and write, primarily associated with a phonological core deficit. However, the manifestation of symptoms in dyslexia also includes impaired working memory (WM). The aim of this study was to investigate cortical activation related to verbal WM in dyslexic and normal readers aged around 13 years, controlling for phonological awareness processing. We used a modified WM n‐back task where the participants remembered the first or last speech segment (phonemes) of the names of common objects shown as pictures. Dyslexic readers were impaired compared with the control group. Compared with the dyslexic readers, controls showed increased fMRI activation in the left superior parietal lobule and the right inferior prefrontal gyrus. Unlike controls, dyslexics did not show a significant increase in activation in WM areas with increased memory load. These findings provide support for a specific working memory deficit in dyslexic individuals.     

Multichannel fNIRS assessment of overt and covert confrontation naming

Confrontation naming tasks assess cognitive processes involved in the main stage of word production. However, in fMRI, the occurrence of movement artifacts necessitates the use of covert paradigms, which has limited clinical applications. Thus, we explored the feasibility of adopting multichannel functional near-infrared spectroscopy (fNIRS) to assess language function during covert and overt naming tasks. Thirty right-handed, healthy adult volunteers underwent both naming tasks and cortical hemodynamics measurement using fNIRS. The overt naming task recruited the classical left-hemisphere language areas (left inferior frontal, superior and middle temporal, precentral, and postcentral gyri) exemplified by an increase in the oxy-Hb signal. Activations were bilateral in the middle and superior temporal gyri. However, the covert naming task recruited activation only in the left-middle temporal gyrus. The activation patterns reflected a major part of the functional network for overt word production, suggesting the clinical importance of fNIRS in the diagnosis of aphasic patients.     

The role of inferior frontal cortex in phonological processing

Recent neuroimaging studies of language processing are examining the neural substrate of phonology because of its critical role in mapping sound information onto higher levels of language processing (e.g., words) as well as providing codes in which verbal information can be temporarily stored in working memory. However, the precise role of the inferior frontal cortex in spoken and written phonological tasks has remained elusive. Although lesion studies have indicated the presence of selective deficits in phonological processing, the location of lesions underlying these impairments has not revealed a consistent pattern. Despite efforts to refine methods and tasks, functional neuroimaging studies have also revealed variability in activation patterns. Reanalysis of evidence from these neuroimaging studies suggests that there are functional subregions within the inferior frontal gyrus that correspond to specific components of phonological processing (e.g., orthographic to phonological conversion in reading, and segmentation in speech).     

Neural correlates in the processing of phoneme-level complexity in vowel production

We investigated how articulatory complexity at the phoneme level is manifested neurobiologically in an overt production task. fMRI images were acquired from young Korean-speaking adults as they pronounced bisyllabic pseudowords in which we manipulated phonological complexity defined in terms of vowel duration and instability (viz., COMPLEX: /ti?i/ >> MID-COMPLEX: /tiye/ >> SIMPLE: /tii/). Increased activity in the left inferior frontal gyrus (Brodmann Areas (BA) 44 and 47), supplementary motor area and anterior insula was observed for the articulation of COMPLEX sequences relative to MID-COMPLEX; this was the case with the articulation of MID-COMPLEX relative to SIMPLE, except that the pars orbitalis (BA 47) was dominantly identified in the Broca’s area. The differentiation indicates that phonological complexity is reflected in the neural processing of distinct phonemic representations, both by recruiting brain regions associated with retrieval of phonological information from memory and via articulatory rehearsal for the production of COMPLEX vowels. In addition, the finding that increased complexity engages greater areas of the brain suggests that brain activation can be a neurobiological measure of articulo-phonological complexity, complementing, if not substituting for, biomechanical measurements of speech motor activity.     

Brain imaging of tongue-twister sentence comprehension: twisting the tongue and the brain

This study used fMRI to investigate the neural basis of the tongue-twister effect in a sentence comprehension task. Participants silently read sentences equated for the syntactic structure and the lexical frequency of the constituent words, but differing in the proportion of words that shared similar initial phonemes. The manipulation affected not only the reading times and comprehension performance, but also the amount of activation seen in a number of language-related cortical areas. The effect was not restricted to cortical areas known to be involved in articulatory speech programming or rehearsal processes (the inferior frontal gyrus and anterior insula), but also extended to areas associated with other aspects of language processing (inferior parietal cortex) associated with phonological processing and storage.     

Reversing spoken items--mind twisting not tongue twisting

Using 12 participants we conducted an fMRI study involving two tasks, word reversal and rhyme judgment, based on pairs of natural speech stimuli, to study the neural correlates of manipulating auditory imagery under taxing conditions. Both tasks engaged the left anterior superior temporal gyrus, reflecting previously established perceptual mechanisms. Engagement of the left inferior frontal gyrus in both tasks relative to baseline could only be revealed by applying small volume corrections to the region of interest, suggesting that phonological segmentation played only a minor role and providing further support for factorial dissociation of rhyming and segmentation in phonological awareness. Most importantly, subtraction of rhyme judgment from word reversal revealed activation of the parietal lobes bilaterally and the right inferior frontal cortex, suggesting that the dynamic manipulation of auditory imagery involved in mental reversal of words seems to engage mechanisms similar to those involved in visuospatial working memory and mental rotation. This suggests that reversing spoken items is a matter of mind twisting rather than tongue twisting and provides support for a link between language processing and manipulation of mental imagery.     

What phonological deficit?

We review a series of experiments aimed at understanding the nature of the phonological deficit in developmental dyslexia. These experiments investigate input and output phonological representations, phonological grammar, foreign speech perception and production, and unconscious speech processing and lexical access. Our results converge on the observation that the phonological representations of people with dyslexia may be intact, and that the phonological deficit surfaces only as a function of certain task requirements, notably short-term memory, conscious awareness, and time constraints. In an attempt to reformulate those task requirements more economically, we propose that individuals with dyslexia have a deficit in access to phonological representations. We discuss the explanatory power of this concept and we speculate that a similar notion might also adequately describe the nature of other associated cognitive deficits when present.     

Dyslexia and dyscalculia: Two learning disorders with different cognitive profiles

This study tests the hypothesis that dyslexia and dyscalculia are associated with two largely independent cognitive deficits, namely a phonological deficit in the case of dyslexia and a deficit in the number module in the case of dyscalculia. In four groups of 8- to 10-year-olds (42 control, 21 dyslexic, 20 dyscalculic, and 26 dyslexic/dyscalculic), phonological awareness, phonological and visual-spatial short-term and working memory, naming speed, and basic number processing skills were assessed. A phonological deficit was found for both dyslexic groups, irrespective of additional arithmetic deficits, but not for the dyscalculia-only group. In contrast, deficits in processing of symbolic and nonsymbolic magnitudes were observed in both groups of dyscalculic children, irrespective of additional reading difficulties, but not in the dyslexia-only group. Cognitive deficits in the comorbid dyslexia/dyscalculia group were additive; that is, they resulted from the combination of two learning disorders. These findings suggest that dyslexia and dyscalculia have separable cognitive profiles, namely a phonological deficit in the case of dyslexia and a deficient number module in the case of dyscalculia.     

Neural dissociation of phonological and visual attention span disorders in developmental dyslexia: FMRI evidence from two case reports

A dissociation between phonological and visual attention (VA) span disorders has been reported in dyslexic children. This study investigates whether this cognitively-based dissociation has a neurobiological counterpart through the investigation of two cases of developmental dyslexia. LL showed a phonological disorder but preserved VA span whereas FG exhibited the reverse pattern. During a phonological rhyme judgement task, LL showed decreased activation of the left inferior frontal gyrus whereas this region was activated at the level of the controls in FG. Conversely, during a visual categorization task, FG demonstrated decreased activation of the parietal lobules whereas these regions were activated in LL as in the controls. These contrasted patterns of brain activation thus mirror the cognitive disorders’ dissociation. These findings provide the first evidence for an association between distinct brain mechanisms and distinct cognitive deficits in developmental dyslexia, emphasizing the importance of taking into account the heterogeneity of the reading disorder.     

Genes, language development, and language disorders

Genetic factors are important contributors to language and learning disorders, and discovery of the underlying genes can help delineate the basic neurological pathways that are involved. This information, in turn, can help define disorders and their perceptual and processing deficits. Initial molecular genetic studies of dyslexia, for example, appear to converge on defects in neuronal and axonal migration. Further study of individuals with abnormalities of these genes may lead to the recognition of characteristic cognitive deficits attributable to the neurological dysfunction. Such abnormalities may affect other disorders as well, and studies of co-morbidity of dyslexia with attention deficit disorder and speech sound disorder are helping to define the scope of these genes and show the etiological and cognitive commonalities between these conditions. The genetic contributions to specific language impairment (SLI) are not as well defined at this time, but similar molecular approaches are being applied to identify genes that influence SLI and comorbid disorders. While there is co-morbidity of SLI with dyslexia, it appears that most of the common genetic effects may be with the language characteristics of autism spectrum disorders rather than with dyslexia and related disorders. Identification of these genes and their neurological and cognitive effects should lay out a functional network of interacting genes and pathways that subserve language development. Understanding these processes can form the basis for refined procedures for diagnosis and treatment.     

The minimal unit of phonological encoding: prosodic or lexical word

Wheeldon and Lahiri (Journal of Memory and Language 37 (1997) 356) used a prepared speech production task (Sternberg, S., Monsell, S., Knoll, R. L., & Wright, C. E. (1978). The latency and duration of rapid movement sequences: comparisons of speech and typewriting. In G. E. Stelmach (Ed.), Information processing in motor control and learning (pp. 117-152). New York: Academic Press; Sternberg, S., Wright, C. E., Knoll, R. L., & Monsell, S. (1980). Motor programs in rapid speech: additional evidence. In R. A. Cole (Ed.), The perception and production of fluent speech (pp. 507-534). Hillsdale, NJ: Erlbaum) to demonstrate that the latency to articulate a sentence is a function of the number of phonological words it comprises. Latencies for the sentence [Ik zoek het] [water] 'I seek the water' were shorter than latencies for sentences like [Ik zoek] [vers] [water] 'I seek fresh water'. We extend this research by examining the prepared production of utterances containing phonological words that are less than a lexical word in length. Dutch compounds (e.g. ooglid 'eyelid') form a single morphosyntactic word and a phonological word, which in turn includes two phonological words. We compare their prepared production latencies to those syntactic phrases consisting of an adjective and a noun (e.g. oud lid 'old member') which comprise two morphosyntactic and two phonological words, and to morphologically simple words (e.g. orgel 'organ') which comprise one morphosyntactic and one phonological word. Our findings demonstrate that the effect is limited to phrasal level phonological words, suggesting that production models need to make a distinction between lexical and phrasal phonology.     

Speaking two languages at once: Unconscious native word form access in second language production

Bilingualism research has established language non-selective lexical access in comprehension. However, the evidence for such an effect in production remains sparse and its neural time-course has not yet been investigated. We demonstrate that German-English bilinguals performing a simple picture-naming task exclusively in English spontaneously access the phonological form of –unproduced– German words. Participants were asked to produce English adjective-noun sequences describing the colour and identity of familiar objects presented as line drawings. We associated adjective and picture names such that their onsets phonologically overlapped in English (e.g., green goat), in German through translation (e.g., blue flower – ‘blaue Blume’), or in neither language. As expected, phonological priming in English modulated event-related brain potentials over the frontocentral scalp region from around 440 ms after picture onset. Phonological priming in German was detectable even earlier, from 300 ms, even though German was never produced and in the absence of an interaction between language and phonological repetition priming at any point in time. Overall, these results establish the existence of non-selective access to phonological representations of the two languages in the domain of speech production.     

The relationship between auditory temporal processing,phonemic awareness,and reading disability

Recent research suggests an auditory temporal deficit as a possible contributing factor to poor phonemic awareness skills. This study investigated the relationship between auditory temporal processing of nonspeech sounds and phonological awareness ability in children with a reading disability, aged 8-12 years, using Tallal's tone-order judgement task. Normal performance on the tone-order task was established for 36 normal readers. Forty-two children with developmental reading disability were then subdivided by their performance on the tone-order task. Average and poor tone-order subgroups were then compared on their ability to process speech sounds and visual symbols, and on phonological awareness and reading. The presence of a tone-order deficit did not relate to performance on the order processing of speech sounds, to poorer phonological awareness or to more severe reading difficulties. In particular, there was no evidence of a group by interstimulus interval interaction, as previously described in the literature, and thus little support for a general auditory temporal processing difficulty as an underlying problem in poor readers. In this study, deficient order judgement on a nonverbal auditory temporal order task (tone task) did not underlie phonological awareness or reading difficulties.     

Effective brain connectivity in children with reading difficulties during phonological processing

Using Dynamic Causal Modeling (DCM) and functional magnetic resonance imaging (fMRI), we examined effective connectivity between three left hemisphere brain regions (inferior frontal gyrus, inferior parietal lobule, fusiform gyrus) and bilateral medial frontal gyrus in 12 children with reading difficulties (M age=12.4, range: 8.11-14.10) and 12 control children (M age=12.3, range: 8.9-14.11) during rhyming judgments to visually presented words. More difficult conflicting trials either had similar orthography but different phonology (e.g. pint-mint) or similar phonology but different orthography (e.g. jazz-has). Easier non-conflicting trials had similar orthography and phonology (e.g. dime-lime) or different orthography and phonology (e.g. staff-gain). The modulatory effect from left fusiform gyrus to left inferior parietal lobule was stronger in controls than in children with reading difficulties only for conflicting trials. Modulatory effects from left fusiform gyrus and left inferior parietal lobule to left inferior frontal gyrus were stronger for conflicting trials than for non-conflicting trials only in control children but not in children with reading difficulties. Modulatory effects from left inferior frontal gyrus to inferior parietal lobule, from medial frontal gyrus to left inferior parietal lobule, and from left inferior parietal lobule to medial frontal gyrus were positively correlated with reading skill only in control children. These findings suggest that children with reading difficulties have deficits in integrating orthography and phonology utilizing left inferior parietal lobule, and in engaging phonological rehearsal/segmentation utilizing left inferior frontal gyrus possibly through the indirect pathway connecting posterior to anterior language processing regions, especially when the orthographic and phonological information is conflicting.     

Production of Inflected Novel Words in Older Adults With and Without Dementia

While cognitive changes in aging and neurodegenerative disease have been widely studied, language changes in these populations are less well understood. Inflecting novel words in a language with complex inflectional paradigms provides a good opportunity to observe how language processes change in normal and abnormal aging. Studies of language acquisition suggest that children inflect novel words based on their phonological similarity to real words they already know. It is unclear whether speakers continue to use the same strategy when encountering novel words throughout the lifespan or whether adult speakers apply symbolic rules. We administered a simple speech elicitation task involving Finnish-conforming pseudo-words and real Finnish words to healthy older adults, individuals with mild cognitive impairment, and individuals with Alzheimer's disease (AD) to investigate inflectional choices in these groups and how linguistic variables and disease severity predict inflection patterns. Phonological resemblance of novel words to both a regular and an irregular inflectional type, as well as bigram frequency of the novel words, significantly influenced participants' inflectional choices for novel words among the healthy elderly group and people with AD. The results support theories of inflection by phonological analogy (single-route models) and contradict theories advocating for formal symbolic rules (dual-route models).