Abstract
Neuroscience findings have recently received critique on the lack of replications. To examine the reproducibility of brain indices of speech sound discrimination and their role in dyslexia, a specific reading difficulty, brain event-related potentials using EEG were measured using the same cross-linguistic passive oddball paradigm in about 200 dyslexics and 200 typically reading 8–12-year-old children from four countries with different native languages. Brain responses indexing speech and non-speech sound discrimination were extremely reproducible, supporting the validity and reliability of cognitive neuroscience methods. Significant differences between typical and dyslexic readers were found when examined separately in different country and language samples. However, reading group differences occurred at different time windows and for different stimulus types between the four countries. This finding draws attention to the limited generalizability of atypical brain response findings in children with dyslexia across language environments and raises questions about a common neurobiological factor for dyslexia. Our results thus show the robustness of neuroscience methods in general while highlighting the need for multi-sample studies in the brain research of language disorders.
Highlights
Neuroscience findings have recently received critique on the lack of replications
Our results show the robustness of change detection related responses in the study of auditory and speech perception while highlighting the need for multi-sample studies in the brain research of language disorders
Our study with four national samples shows results, which could have been interpreted, if they had been found in separate studies, as an indicator of a general impairment in basic auditory or speech processing in dyslexic readers as it has previously been suggested in several studies (e.g.11,19)
Summary
Neuroscience findings have recently received critique on the lack of replications. To examine the reproducibility of brain indices of speech sound discrimination and their role in dyslexia, a specific reading difficulty, brain event-related potentials using EEG were measured using the same crosslinguistic passive oddball paradigm in about 200 dyslexics and 200 typically reading 8–12-year-old children from four countries with different native languages. An increasing number of studies currently report single results, which can be false positive findings unless they are replicated[2] This applies to the past two decades of research uncovering causes of developmental dyslexia, a disorder leading to dysfluent reading in about 3–7% of the population[3]. Atypical MMN11–18 or LDN13,19 in dyslexia are independently reported by different research groups from several language environments, for example Chinese, English, Finnish, German, Hungarian (for reviews, see[20,21]) This might seem to imply that the altered MMN in dyslexia is a universal phenomenon. MMN in individuals with dyslexia have been sometimes found exclusively for speech sounds and sometimes for non-speech sounds[23,24,25] This indicates the possibility that experimental designs, study samples or stability of the ERP responses can lead to slightly different results in the group comparisons. We (1) selected dyslexic and control participants according to the same procedure, using nationally normed behavioral tests for reading fluency, (2) used the same stimulus set and experimental procedure, (3) applied the same data recording parameters and processing steps to extract averaged ERPs, and (4) followed a systematic and automatized analysis procedure using R packages[26] (see Materials and methods)
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