Franck Ramus

Neurobiology of dyslexia: a reinterpretation of the data

Theories of developmental dyslexia differ on how to best interpret the great variety of symptoms (linguistic, sensory and motor) observed in dyslexic individuals. One approach views dyslexia as a specific phonological deficit, which sometimes co-occurs with a more general sensorimotor syndrome. This article on the neurobiology of dyslexia shows that neurobiological data are indeed consistent with this view, explaining both how a specific phonological deficit might arise, and why a sensorimotor syndrome should be significantly associated with it. This new conceptualisation of the aetiology of dyslexia could generalize to other neurodevelopmental disorders, and might further explain heterogeneity within each disorder and comorbidity between disorders.

The relationship between motor control and phonology in dyslexic children

BACKGROUNDnThe goal of this study was to investigate the automaticity/cerebellar theory of dyslexia. We tested phonological skills and cerebellar function in a group of dyslexic 8-12-year-old children and their matched controls. Tests administered included the Phonological Assessment Battery, postural stability, bead threading, finger to thumb and time estimation.nnnRESULTSnDyslexic children were found to be significantly poorer than the controls at all tasks but time estimation. About 77% of dyslexics were more than one standard deviation below controls in phonological ability, and 59% were similarly impaired in motor skills. However, at least part of the discrepancy in motor skills was due to dyslexic individuals who had additional disorders (ADHD and/or DCD). The absence of evidence for a time estimation deficit also casts doubt on the cerebellar origin of the motor deficiency. About half the dyslexic children didnt have any motor problem, and there was no evidence for a causal relationship between motor skills on the one hand and phonological and reading skills on the other.nnnCONCLUSIONnThis study provides partial support for the presence of motor problems in dyslexic children, but does not support the hypothesis that a cerebellar dysfunction is the cause of their phonological and reading impairment.

Perception and acquisition of linguistic rhythm by infants

In the present paper, we address the issue of the emergence in infancy of speech segmentation procedures that were found to be specific to rhythmic classes of languages in adulthood. These metrical procedures, which segment fluent speech into its constitutive word sequence, are crucial for the acquisition by infants of the words of their native language. We first present a prosodic bootstrapping proposal according to which the acquisition of these metrical segmentation procedures would be based on an early sensitivity to rhythm (and rhythmic classes). We then review several series of experiments that have studied infants ability to discriminate languages between birth and 5 months, in an attempt to specify their sensitivity to rhythm and the implication of rhythm perception in the acquisition of these segmentation procedures. The results presented here establish infants sensitivity to rhythmic classes (from birth onwards). They further show an evolution of infants language discriminations between birth and 5 months which, though not inconsistent with our proposal, nevertheless call for more studies on the possible implication of rhythm in the acquisition of the metrical segmentation procedures.

Enhanced perceptual processing of speech in autism

Theories of autism have proposed that a bias towards low-level perceptual information, or a featural/surface-biased information-processing style, may compromise higher-level language processing in such individuals. Two experiments, utilizing linguistic stimuli with competing low-level/perceptual and high-level/semantic information, tested processing biases in children with autism and matched controls. Whereas children with autism exhibited superior perceptual processing of speech relative to controls, and showed no evidence of either a perceptual or semantic processing bias, controls showed a tendency to process speech semantically. The data provide partial support to the perceptual theories of autism. It is additionally proposed that the pattern of results may reflect different patterns of attentional focusing towards single or multiple stimulus cues in speech between children with autism and controls.

Dyslexia - Talk of two theories

One possible reason why people with dyslexia have problems in learning to read is that some neuronal pathways involved in vision and hearing are damaged. That theory may need to be revised.

A double dissociation between sensorimotor impairments and reading disability : A comparison of autistic and dyslexic children

Does sensorimotor dysfunction underlie reading impairment? To investigate this question, a battery of literacy, phonology, auditory, visual, and motor tests were administered to age- and ability-matched groups of dyslexic, autistic, and control children. As in previous studies, only a subset of the dyslexic children had sensory and/or motor impairments, whilst some dyslexics were entirely spared, suggesting that sensorimotor impairments are not necessary to cause reading disability. A subset of autistic children was also found to have sensorimotor impairments; however, some of these children did not have reading problems, suggesting that sensorimotor impairments are not sufficient to cause reading disability. We conclude that sensorimotor and reading impairments are doubly dissociable. Sensorimotor impairments do not seem to be the cause of reading disability, but can be seen as nonspecific markers for developmental disorder.