Abstract
Studies of the performance of individuals with dyslexia in perceptual tasks suggest that their implicit inference of sound statistics is impaired. Previously, using two-tone frequency discrimination, we found that the effect of previous trials' frequencies on the judgments of individuals with dyslexia decays faster than the effect on controls' judgments, and that the adaptation (decrease of neural response to repeated stimuli) of their ERP responses to tones is shorter (<xref ref-type="bibr" rid="bib22">Jaffe-Dax et al., 2017</xref>). Here, we show the cortical distribution of these abnormal dynamics of adaptation using fast-acquisition fMRI. We find that faster decay of adaptation in dyslexia is widespread, although the most significant effects are found in the left superior temporal lobe, including the auditory cortex. This broad distribution suggests that the faster decay of implicit memory of individuals with dyslexia is a general characteristic of their cortical dynamics, which also affects sensory cortices.
Highlights
Dyslexia, a specific and significant impairment in the development of reading skills that is not accounted for by mental age, visual acuity problems, or inadequate schooling (World Health Organization, 2016), affects ~5% of the world’s population (Lindgren et al, 1985)
Good readers performed better than dyslexic participants (Mean ± SEM: 82.5 ± 1.6% vs. 76.3 ± 2.2%, z = 2.6, p
For each of these voxels, we calculated the dynamics of adaptation, among control participants and among participants with dyslexia, as follows
Summary
A specific and significant impairment in the development of reading skills that is not accounted for by mental age, visual acuity problems, or inadequate schooling (World Health Organization, 2016), affects ~5% of the world’s population (Lindgren et al, 1985). Though individuals with dyslexia are diagnosed for their reading impairments, they often have difficulties in simple non-linguistic perceptual tasks (Mcanally and Stein, 1996; Ahissar et al, 2000; Sperling et al, 2005; Giraud and Ramus, 2013) These can be largely explained as resulting from inefficient use of stimulus statistics that characterize the experiment (the ‘Anchoring Deficit hypothesis’; Ahissar et al, 2006; Oganian and Ahissar, 2012; Jaffe-Dax et al, 2015). In these tasks, participants are not aware of the effect of previous stimuli. This contraction to the mean merges the (implicit) predicted stimulus (based on previous exposures) with the current sensory estimate, forming a coherent percept
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