Deficits in Letter-Speech Sound Associations but Intact Visual Conflict Processing in Dyslexia: Results from a Novel ERP-Paradigm

Abstract

The reading and spelling deficits characteristic of developmental dyslexia (dyslexia) have been related to problems in phonological processing and in learning associations between letters and speech-sounds. Even when children with dyslexia have learned the letters and their corresponding speech sounds, letter-speech sound associations might still be less automatized compared to children with age-adequate literacy skills. In order to examine automaticity in letter-speech sound associations and to overcome some of the disadvantages associated with the frequently used visual-auditory oddball paradigm, we developed a novel electrophysiological letter-speech sound interference paradigm. This letter-speech sound interference paradigm was applied in a group of 9-year-old children with dyslexia (n = 36) and a group of typically developing (TD) children of similar age (n = 37). Participants had to indicate whether two letters look visually the same. In the incongruent condition (e.g., the letter pair A-a) there was a conflict between the visual information and the automatically activated phonological information; although the visual appearance of the two letters is different, they are both associated with the same speech sound. This conflict resulted in slower response times (RTs) in the incongruent than in the congruent (e.g., the letter pair A-e) condition. Furthermore, in the TD control group, the conflict resulted in fast and strong event-related potential (ERP) effects reflected in less negative N1 amplitudes and more positive conflict slow potentials (cSP) in the incongruent than in the congruent condition. However, the dyslexic group did not show any conflict-related ERP effects, implying that letter-speech sound associations are less automatized in this group. Furthermore, we examined general visual conflict processing in a control visual interference task, using false fonts. The conflict in this experiment was based purely on the visual similarity of the presented objects. Visual conflict resulted in slower RTs, less negative N2 amplitudes and more positive cSP in both groups. Thus, on a general, basic level, visual conflict processing does not seem to be affected in children with dyslexia.

Deficient Letter-Speech Sound Integration Is Associated With Deficits in Reading but Not Spelling

“…Similar results were borne out by Bakos et al ( 2017 ), using an adapted Stroop-like letter-speech sound interference paradigm (Posner and Mitchell, 1967 ). Throughout the task, participants saw two letters, and had to decide whether the two letters are visually identical or not by pressing a response key.…”

“…Conflict emerges from the same letters presented in different cases (e.g., “T t”): they are visually different but are associated with the same phoneme. A novel ERP study used this task to compare neural correlates of conflict in RSD and TD children, and found a similar reaction time (RT) increase to conflict trials in both groups, but conflict-related ERP amplitude modulation was missing in RSD (Bakos et al, 2017 ).…”

“…However, knowing letters and corresponding speech-sounds is not sufficient to develop proficient reading; these associations also need to be automatized (letter-sound integration hypothesis, Blomert, 2011 ). It has been suggested that letter-speech sound integration is deficient in poor readers (Bakos et al, 2017 ). The current experiment tests the automaticity of letter-speech sound associations with a Stroop-like interference task in 9-year-old children with developmental dyslexia—conceptualized as combined reading and spelling deficit (RSD), a group with isolated spelling deficit (ISD), and a group of typically developing (TD) children.…”

“…The following section reviews previous results of letter-speech sound associations in dyslexia, and describes a classical method (Posner and Mitchell, 1967 ) that has been applied to assess letter-speech sound associations using event-related potential (ERP) in a novel study (Bakos et al, 2017 ). Since the current study is an ERP study, the introduction follows with the description of conflict-related ERP components, and then turns to the description of the current study.…”

A Longitudinal Study of Early Reading Development: Letter-Sound Knowledge, Phoneme Awareness and RAN, but Not Letter-Sound Integration, Predict Variations in Reading Development

“…Most studies that support this hypothesis are concurrent ERP or fMRI studies comparing lettersound processing in small groups of children or adults with dyslexia, to typically developing readers matched for age (Bakos, Landerl, Bartling, Schulte-Körne, & Moll, 2017;Blau et al, 2010;Blau, van Atteveldt, Ekkebus, Goebel, & Blomert, 2009;Jones, Kuipers, & Thierry, 2016;Karipidis et al, 2017;Kronschnabel, Brem, Maurer, & Brandeis, 2014;Moll, Hasko, Groth, Bartling, & Schulte-Körne, 2016). These studies report atypical (or developmentally delayed) associations between letters and speech-sounds in children with dyslexia, but with little agreement between different studies.…”