Virginie Daffaure | PubMed Health

PubMed2002

Interhemispheric sensorimotor integration in pointing movements: a study on dyslexic adults.

In addition to reading disorders, numerous deficits have been found to be associated with dyslexia, suggesting that various neurological factors might be involved in its etiology. In the present study, we focused on three of the deficits which have been thought to accompany and to a certain extent, to explain dyslexia: an abnormal pattern of hemispheric asymmetry, abnormal hemispheric communication, and abnormal motor control. The aim of the present study was to determine whether adults with reading difficulties perform differently from control subjects in a visuo-manual pointing task, in which the subject was required to point with the right or the left hand to targets appearing to the right or left of a central fixation point. A total of 14 dyslexic adults and 14 control adults participated in this experiment. Motor control was assessed based on the time taken to perform the pointing task, hemispheric asymmetry in terms of the inter-hand differences in the reaction and movement times, and hemispheric communication based on the interhemispheric transfer time under crossed conditions, where the hand and the target were not on the same side. The results showed that neither hemispheric asymmetry nor interhemispheric transfer differed between dyslexic and control adults. However, the dyslexics were significantly slower when performing the pointing task. These results are in agreement with the hypothesis that dyslexia may involve a mild motor deficit.

Adult↗

PubMedDate not supplied

Phonological training in children with dyslexia using temporally modified speech: a three-step pilot investigation.

Three separate studies were successively carried out to investigate the usefulness of intensively training children with dyslexia with daily exercizes based on the temporal processing theory of dyslexia, according to which these children would be specifically unable to process brief and rapidly changing auditory stimuli. The speech modification, similar for the three studies, was close to that proposed by Merzenich et al. (1996) and Tallal et al. (1996), including both artificial slowing of natural speech stimuli and amplification of brief, unstable portions of the speech signal. In the first study, 12 children, aged 10-12 years, received either such modified speech or normal speech for 1 h a day, 5 days a week, over 5 weeks, and they were assessed on phonological tasks before, during and after training. A significant advantage for the modified speech group was found both in pre-post-training improvement and in day-to-day progression on phonological performance. In a second study, 29 children with dyslexia, aged 5-12, received a similar training, but for only 15 min a day, 7 days a week, over 6 weeks, part at the speech therapist office, part in their own homes. The finding of comparable improvement in a more 'natural' environment and in children over a wider age range indicates both the efficacy and feasibility of the method in usual clinical practice. However, this study also showed that one of four children did not improve as expected, prompting a third study where 23 other children underwent specific tasks presumably exploring various aspects of temporal processing in order to find predictors of training efficacy. A 'temporal order judgement' (TOJ) task was found best correlated with post-training improvement, suggesting that one use this task for selecting the best candidates for temporo-phonological training. Moreover, such correlation provided further argument in favour of the temporal deficit theory of dyslexia, not only by showing a link between a purely temporal task and ultimate phonological performance, but also by demonstrating that TOJ performance itself improves after phonological training. Finally, and taken together, these studies provide further justification for a rational, indication-based temporo-phonological treatment of dyslexia. Possible neural substrates of the relevant mechanisms are discussed in the light of recent experimental and brain-imaging studies.

Child↗