Evidence for a specific cross‐modal association deficit in dyslexia: an electrophysiological study of letter–speech sound processing

Abstract

The phonological deficit theory of dyslexia assumes that degraded speech sound representations might hamper the acquisition of stable letter-speech sound associations necessary for learning to read. However, there is only scarce and mainly indirect evidence for this assumed letter-speech sound association problem. The present study aimed at clarifying the nature and the role of letter-speech sound association problems in dyslexia by analysing event-related potentials (ERP) of 11-year-old dyslexic children to speech sounds in isolation or combined with letters, which were presented either simultaneously with or 200 ms before the speech sounds. Recent studies with normal readers revealed that letters systematically modulated speech sound processing in an early (mismatch negativity or MMN) and late (Late Discriminatory Negativity or LDN) time-window. The amplitude of the MMN and LDN to speech sounds was enhanced when speech sounds were presented with letters. The dyslexic readers in the present study, however, did not exhibit any early influences of letters on speech sounds even after 4 years of reading instruction, indicating no automatic integration of letters and speech sounds. Interestingly, they revealed a systematic late effect of letters on speech sound processing, probably reflecting the mere association of letters and speech sounds. This pattern is strongly divergent from that observed in age-matched normal readers, who showed both early and late effects, but reminiscent of that observed in beginner normal readers in a previous study (Froyen, Bonte, van Atteveldt & Blomert, 2009). The finding that the quality of letter-speech sound processing is directly related to reading fluency urges further research into the role of audiovisual integration in the development of reading failure in dyslexia.

A General Audiovisual Temporal Processing Deficit in Adult Readers With Dyslexia

“…The MMN is evoked in an oddball paradigm when, in a sequence of auditory stimuli, a rarely presented sound (the deviant) deviates from a frequently presented sound (the standard). Typical readers showed an enhancement of the MMN in response to deviant spoken syllables compared with standards when letters were presented with the speech stimuli (Froyen, Willems, & Blomert, 2011) but not when scrambled images were presented with the speech (Mittag, Thesleff, Laasonen, & Kujala, 2013). This enhancement of the MMN was absent in children with dyslexia (Froyen et al, 2011) and adults (Mittag et al, 2013).…”

“…This enhancement of the MMN was absent in children with dyslexia (Froyen et al, 2011) and adults (Mittag et al, 2013). The lack of enhancement of the MMN in people with dyslexia suggests that early and automatic letter-speech sound integration is absent (Froyen et al, 2011;Mittag et al, 2013).…”

“…Typical readers showed an enhancement of the MMN in response to deviant spoken syllables compared with standards when letters were presented with the speech stimuli (Froyen, Willems, & Blomert, 2011) but not when scrambled images were presented with the speech (Mittag, Thesleff, Laasonen, & Kujala, 2013). This enhancement of the MMN was absent in children with dyslexia (Froyen et al, 2011) and adults (Mittag et al, 2013). The lack of enhancement of the MMN in people with dyslexia suggests that early and automatic letter-speech sound integration is absent (Froyen et al, 2011;Mittag et al, 2013).…”

Beyond the usual cognitive suspects: The importance of speechreading and audiovisual temporal sensitivity in reading ability

“…As mentioned before, reading impairment might reflect a deficit in audiovisual processing and, indeed, children and adult dyslexic readers have been shown to inadequately process audiovisual objects, for instance, while being presented with audiovisual and unisensory letters and speech sounds (Blau, van Atteveldt, Ekkebus, Goebel, & Blomert, 2009;Blau et al, 2010;Froyen, Willems, & Blomert, 2011;Kast, Bezzola, Jäncke, & Meyer, 2011;Kronschnabel, Brem, Maurer, & Brandeis, 2014;Mittag, Thesleff, Laasonen, & Kujala, 2013), while identifying unisensory and audiovisual speech (e.g., Hayes, Tiippana, Nicol, Sams, & Kraus, 2003), and while matching non-linguistic audiovisual materials (e.g., rectangles and tones, Widmann, Schröger, Tervaniemi, Pakarinen, & Kujala, 2012). For a subset of the sample of participants tested in this study, we have recently shown differences between dyslexic and typical adult readers in their audiovisual temporal sensitivity (Francisco, Jesse, Groen, & McQueen, 2017).…”

EEG Resting State Functional Connectivity in Adult Dyslexics Using Phase Lag Index and Graph Analysis

“…These systems include auditory processing, multisensory integration and visual processing areas, their mutual interactions playing an important role at different stages of reading development (see review in Schlaggar and McCandliss, 2007). Neuroimaging studies of dyslexia have suggested deficits in activation of specific brain areas (e.g., Pugh et al, 2000a; Shaywitz et al, 2002; Froyen et al, 2011; Fraga González et al, 2014; Kronschnabel et al, 2014; Žarić et al, 2014) as well as in connectivity across the various brain systems for reading (Horwitz et al, 1998; Pugh et al, 2000b; Quaglino et al, 2008; van der Mark et al, 2011; Žarić et al, 2017). Studies using diffusion tensor imaging (DTI) suggested that dyslexics and typical readers may differ in the main white matter pathways that constitute the anatomical basis of the reading network (see review and meta-analysis in Vandermosten et al, 2012).…”