Are the literacy difficulties that characterize developmental dyslexia associated with a failure to integrate letters and speech sounds?

Hannah M Nash,Margaret J Snowling,Genevieve Mcarthur,Charles Hulme,Kurt Steinmetzger,Debbie Gooch,Yatin Mahajan

doi:10.1111/desc.12423

Abstract

The ‘automatic letter‐sound integration hypothesis’ (Blomert, 2011) proposes that dyslexia results from a failure to fully integrate letters and speech sounds into automated audio‐visual objects. We tested this hypothesis in a sample of English‐speaking children with dyslexic difficulties (N = 13) and samples of chronological‐age‐matched (CA; N = 17) and reading‐age‐matched controls (RA; N = 17) aged 7–13 years. Each child took part in two priming experiments in which speech sounds were preceded by congruent visual letters (congruent condition) or Greek letters (baseline). In a behavioural experiment, responses to speech sounds in the two conditions were compared using reaction times. These data revealed faster reaction times in the congruent condition in all three groups. In a second electrophysiological experiment, responses to speech sounds in the two conditions were compared using event‐related potentials (ERPs). These data revealed a significant effect of congruency on (1) the P1 ERP over left frontal electrodes in the CA group and over fronto‐central electrodes in the dyslexic group and (2) the P2 ERP in the dyslexic and RA control groups. These findings suggest that our sample of English‐speaking children with dyslexic difficulties demonstrate a degree of letter‐sound integration that is appropriate for their reading level, which challenges the letter‐sound integration hypothesis.

Highlights

Dyslexia is a difficulty in learning to read that affects 3– 8% of children (Peterson & Pennington, 2012)
According to a recent alternative hypothesis, the cause of dyslexia is a failure to adequately integrate letters and speech sounds into fully automated audiovisual objects, which in turn arises from a neural crossmodal binding deficit (Blomert, 2011)
Using children’s behavioural and event-related potentials (ERPs) responses in the congruent and baseline conditions of the priming task, we addressed three aims: 1 To determine whether typically developing (TD) children learning to read in English show evidence of automatic letter-sound integration’ (LSI) at the level of behaviour or the brain and whether there are developmental differences in this related to age or reading experience

Summary

Introduction

Dyslexia is a difficulty in learning to read that affects 3– 8% of children (Peterson & Pennington, 2012). The ‘letter-sound integration’ (LSI) hypothesis distinguishes between knowing letter sounds, and the development of automatic associations. Such automatic associations enable the efficient activation of speech sounds from letters that are essential for decoding. According to the LSI hypothesis, it is a lack of automatization that causes the decoding problems that characterize dyslexia. The purpose of the current study was to test the validity of the LSI hypothesis in English-speaking children with dyslexia. Children completed the Sight Word Efficiency (SWE) and Phonetic Decoding Efficiency (PDE) subtests from the Test of Word Reading Efficiency (TOWRE; Torgesen et al, 1999). Children read as many words or nonwords as possible in 45 seconds

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