Abstract
Poor neural speech discrimination has been connected to dyslexia, and may represent phonological processing deficits that are hypothesized to be the main cause for reading impairments. Thus far, neural speech discrimination impairments have rarely been investigated in adult dyslexics, and even less by examining sources of neuromagnetic responses. We compared neuromagnetic speech discrimination in dyslexic and typical readers with mismatch fields (MMF) and determined the associations between MMFs and reading-related skills. We expected weak and atypically lateralized MMFs in dyslexic readers, and positive associations between reading-related skills and MMF strength. MMFs were recorded to a repeating pseudoword /ta-ta/ with occasional changes in vowel identity, duration, or syllable frequency from 43 adults, 21 with confirmed dyslexia. Phonetic (vowel and duration) changes elicited left-lateralized MMFs in the auditory cortices. Contrary to our hypothesis, MMF source strengths or lateralization did not differ between groups. However, better verbal working memory was associated with stronger left-hemispheric MMFs to duration changes across groups, and better reading was associated with stronger right-hemispheric late MMFs across speech-sound changes in dyslexic readers. This suggests a link between neural speech processing and reading-related skills, in line with previous work. Furthermore, our findings suggest a right-hemispheric compensatory mechanism for language processing in dyslexia. The results obtained promote the use of MMFs in investigating reading-related brain processes.
Highlights
In developmental dyslexia, which is highly prevalent and cumbersome for individuals in modern societies, reading-skill acquisition is compromised despite appropriate education and normal intelligence (Lyon et al, 2003)
Dyslexia has been associated with significant difficulties in phonological processing (Laasonen et al, 2010; Ramus, 2001; Ramus et al, 2018), which may result from poor phonological representations or their accessibility (Ramus, 2001; Ramus et al, 2013)
Acoustic–phonological processes pertinent for speech functions can be investigated with mismatch negativity (MMN) responses recorded by electroencephalography (EEG) or magnetoencephalography (MEG; N€a€at€anen, 2001)
Summary
In developmental dyslexia, which is highly prevalent (up to 17%, Elliot and Grigorenko, 2014) and cumbersome for individuals in modern societies, reading-skill acquisition is compromised despite appropriate education and normal intelligence (Lyon et al, 2003). Dyslexia has been associated with several structural and functional brain abnormalities relevant for speech and language processing (Eckert et al, 2016; Giraud and Poeppel, 2012; Lehongre et al, 2011; Linkersdo€rfer et al, 2012; Richlan et al, 2013, 2011; 2009; Schulte-Ko€rne et al, 2001). Acoustic–phonological processes pertinent for speech functions can be investigated with mismatch negativity (MMN) responses recorded by electroencephalography (EEG) or magnetoencephalography (MEG; N€a€at€anen, 2001). The left-hemisphere generator contributes more to speech processing than the right one, presumably reflecting native phonology (e.g., N€a€at€anen et al, 1997; Shestakova et al, 2002; Shtyrov et al, 2000)
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