Gertsovski, A. & Ahissar, M.
The Hebrew University of Jerusalem
Developmental dyslexia has been associated with a difficulty in efficient long-term use of task-relevant statistics in the environment (the 'anchoring deficit' hypothesis; Ahissar et. al, 2006). While adequate readers are able to 'anchor' to repeated stimuli and perform faster and more accurately in reading, language and perceptual tasks that include useful repetitions, individuals with dyslexia fail to do so. We now asked which brain areas show reduced sensitivity to sound statistics. Adult participants with and without dyslexia performed a two-tone frequency discrimination task during fMRI scanning. We tested performance and neural activity in conditions with and without repetition of the first tone in each pair. Control participants benefited more from stimulus repetition, and this successful learning was associated with reduced activity in the primary auditory cortex. In contrast, individuals with dyslexia showed reduced behavioral gain from repetition, and no reduction in activity in the primary auditory cortex. The two groups showed opposite activity patterns in higher-level auditory cortices, suggesting that while beneficial repetition enabled the control group to perform the repetition condition automatically using low-level predictions, the dyslexia group had to develop complex higher-level strategies for dealing with this condition.