Badcock, N. 1 , Ewing, L. 2 , Preece, K. 1 , Jeffery, L. 2 , Rhodes, G. 2 & McArthur, G. 1
1 ARC Centre of Excellence in Cognition and its Disorders, Macquarie University
2 ARC Centre of Excellence in Cognition and its Disorders, University of Western Australia
We investigated auditory perceptual anchoring in dyslexia using a frequency discrimination (FD) task, as described by Ahissar et al. (2006, Nature Neuroscience, doi:10.1038/nn1800). We recruited 24 6- to 13-year-old children whose accuracy for reading regular words, irregular words, or non-words fell below the average range for their age. We also recruited 19 children with age-appropriate regular, irregular, and non-words reading accuracy (controls). In two FD conditions, children were presented with two tones between 1000 and 1500 Hz and asked to judge whether the first or second tone was higher in pitch. In the ?standard? condition one of the two tones was always 1000 Hz. In the ?no standard? condition, one tone was randomly chosen between 1000 and 1400 Hz. Previous work by Ahissar et al. (2006) has demonstrated that controls produce poorer (i.e., higher) thresholds in the ?no standard? condition than the ?standard? condition. In contrast, children with dyslexia perform equally poorly in both conditions. In this study, our group analysis replicated this effect. However, analysis of the individual data revealed two subgroups within the dyslexia group. The largest subgroup produced poor thresholds in both the ?standard? and ?no standard? condition. In contrast, a smaller subgroup performed well in the ?standard? condition and very poorly in the ?no standard? condition. Further comparison of these subgroups revealed that the smaller subgroup group had performed significantly better on language measures (non-word repetition and recalling sentences). A regression analysis within the dyslexia group revealed that non-word repetition and poor non-word reading significantly predicted ?standard? FD thresholds. Considered together, these findings suggest that only a subgroup of children with dyslexia have perceptual anchoring deficits, and these children tend to perform poorly on reading, language, and psychoacoustic tasks that tax the ability to reproduce the order of sounds.