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Atypical cerebral lateralisation in adults with compensated developmental dyslexia demonstrated using functional transcranial Doppler ultrasound.

Illingworth S, Bishop DV - Brain Lang (2009)

Bottom Line: In this study fTCD was used to compare functional asymmetry during a word generation task between a group of 30 dyslexic adults and a group of 30 non-dyslexic individuals.We know from previous research that most people with atypical language lateralisation have normal language and literacy skills: nevertheless, our results confirm that language laterality is reduced in those with dyslexia.Theoretical explanations for this apparent conundrum are discussed.

View Article: PubMed Central - PubMed

Affiliation: University of Oxford, Department of Experimental Psychology, OX1 3UD, United Kingdom.

ABSTRACT
Functional transcranial Doppler ultrasound (fTCD) is a relatively new and non-invasive technique that assesses cerebral lateralisation through measurements of blood flow velocity in the middle cerebral arteries. In this study fTCD was used to compare functional asymmetry during a word generation task between a group of 30 dyslexic adults and a group of 30 non-dyslexic individuals. In light of previous evidence of atypical laterality in dyslexia, a reduced leftward asymmetry was predicted and confirmed. We know from previous research that most people with atypical language lateralisation have normal language and literacy skills: nevertheless, our results confirm that language laterality is reduced in those with dyslexia. Theoretical explanations for this apparent conundrum are discussed.

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Related in: MedlinePlus

Scatterplot showing distribution of laterality indices on word generation task for non-dyslexic and dyslexic males (squares) and females (triangles).
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fig1: Scatterplot showing distribution of laterality indices on word generation task for non-dyslexic and dyslexic males (squares) and females (triangles).

Mentions: Fig. 1 shows a scatterplot of the laterality indices (LI) for the word generation paradigm for non-dyslexic and dyslexic groups. Inspection of the figure suggests that dyslexics (M = 1.65, SD = 2.15) show less left lateralisation than non-dyslexics (M = 3.19, SD = 1.61). Because of skew in the data, we also considered degree of overlap between groups, and found that 73% of the dyslexics scored below the control mean; for normally distributed data this would correspond to an effect size (Cohen’s d) of 0.6. A Mann–Whitney test was used to test the significance of the difference; U = 267, p (2-tailed) = .007. In addition, the standard error of each participant’s LI was used to compute a 95% confidence interval to determine if it differed significantly from zero. This showed that of the non-dyslexics, 28 were left-lateralised, none was right-lateralised and two were bilateral (i.e. the LI was not significantly different from zero). For the participants with dyslexia, 23 were left-lateralised, four were right-lateralised and three were bilateral. The difference in frequency of left-lateralised cases between the dyslexic and non-dyslexic groups just fell short of statistical significance, Fisher exact test, p = .073. As can be seen from the scatter-plot, the quantitative analysis appears more sensitive to the group difference because the dyslexic distribution is shifted from leftward bias across the range, leading not only to more bilateral and right-lateralised cases, but also to fewer cases of strong left lateralisation. In addition, the correlation between the handedness quotient and the LI on fTCD was close to zero, r(60) = .06, p = .667.


Atypical cerebral lateralisation in adults with compensated developmental dyslexia demonstrated using functional transcranial Doppler ultrasound.

Illingworth S, Bishop DV - Brain Lang (2009)

Scatterplot showing distribution of laterality indices on word generation task for non-dyslexic and dyslexic males (squares) and females (triangles).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2977530&req=5

fig1: Scatterplot showing distribution of laterality indices on word generation task for non-dyslexic and dyslexic males (squares) and females (triangles).
Mentions: Fig. 1 shows a scatterplot of the laterality indices (LI) for the word generation paradigm for non-dyslexic and dyslexic groups. Inspection of the figure suggests that dyslexics (M = 1.65, SD = 2.15) show less left lateralisation than non-dyslexics (M = 3.19, SD = 1.61). Because of skew in the data, we also considered degree of overlap between groups, and found that 73% of the dyslexics scored below the control mean; for normally distributed data this would correspond to an effect size (Cohen’s d) of 0.6. A Mann–Whitney test was used to test the significance of the difference; U = 267, p (2-tailed) = .007. In addition, the standard error of each participant’s LI was used to compute a 95% confidence interval to determine if it differed significantly from zero. This showed that of the non-dyslexics, 28 were left-lateralised, none was right-lateralised and two were bilateral (i.e. the LI was not significantly different from zero). For the participants with dyslexia, 23 were left-lateralised, four were right-lateralised and three were bilateral. The difference in frequency of left-lateralised cases between the dyslexic and non-dyslexic groups just fell short of statistical significance, Fisher exact test, p = .073. As can be seen from the scatter-plot, the quantitative analysis appears more sensitive to the group difference because the dyslexic distribution is shifted from leftward bias across the range, leading not only to more bilateral and right-lateralised cases, but also to fewer cases of strong left lateralisation. In addition, the correlation between the handedness quotient and the LI on fTCD was close to zero, r(60) = .06, p = .667.

Bottom Line: In this study fTCD was used to compare functional asymmetry during a word generation task between a group of 30 dyslexic adults and a group of 30 non-dyslexic individuals.We know from previous research that most people with atypical language lateralisation have normal language and literacy skills: nevertheless, our results confirm that language laterality is reduced in those with dyslexia.Theoretical explanations for this apparent conundrum are discussed.

View Article: PubMed Central - PubMed

Affiliation: University of Oxford, Department of Experimental Psychology, OX1 3UD, United Kingdom.

ABSTRACT
Functional transcranial Doppler ultrasound (fTCD) is a relatively new and non-invasive technique that assesses cerebral lateralisation through measurements of blood flow velocity in the middle cerebral arteries. In this study fTCD was used to compare functional asymmetry during a word generation task between a group of 30 dyslexic adults and a group of 30 non-dyslexic individuals. In light of previous evidence of atypical laterality in dyslexia, a reduced leftward asymmetry was predicted and confirmed. We know from previous research that most people with atypical language lateralisation have normal language and literacy skills: nevertheless, our results confirm that language laterality is reduced in those with dyslexia. Theoretical explanations for this apparent conundrum are discussed.

Show MeSH
Related in: MedlinePlus