Late, not early mismatch responses to changes in frequency are reduced or deviant in children with dyslexia: an event-related potential study.

Lorna F Halliday,Johanna G Barry,Dorothy Vm Bishop,Mervyn J Hardiman

doi:10.1186/1866-1955-6-21

Abstract

BackgroundDevelopmental disorders of oral and written language have been linked to deficits in the processing of auditory information. However, findings have been inconsistent, both for behavioural and electrophysiological measures.MethodsIn this study, we examined event-related potentials (ERPs) in 20 6- to 14-year-old children with developmental dyslexia and 20 age-matched controls, divided into younger (6–11 years, n = 10) and older (11–14 years, n = 10) age bands. We focused on early (mismatch negativity; MMN) and late (late discriminative negativity; LDN) conventional mismatch responses and associated measures derived from time-frequency analysis (inter-trial coherence and event-related spectral perturbation). Responses were elicited using an auditory oddball task, whereby a stream of 1000-Hz standards was interspersed with rare large (1,200 Hz) and small (1,030 Hz) frequency deviants.ResultsConventional analyses revealed no significant differences between groups in the size of the MMN to either large or small frequency deviants. However, the younger age band of children with dyslexia showed an enhanced inter-trial coherence in the theta frequency band over the time window corresponding to the MMN to small deviants. By contrast, these same children showed a reduced-amplitude LDN for the small deviants relative to their age-matched controls, whilst the older children with dyslexia showed a shorter and less intense period of event-related desynchronization over this time window.ConclusionsInitial detection and discrimination of auditory frequency change appears normal or even enhanced in children with dyslexia. Rather, deficits in late-stage auditory processing appear to be a feature of this population.

Highlights

Developmental disorders of oral and written language have been linked to deficits in the processing of auditory information
We focused our analyses on the intertrial coherence (ITC) and event-related spectral perturbation (ERSP) in the theta range that corresponded to the periods associated with the MMN and late discriminative negativity (LDN), respectively
Because of the differences in stimuli between the two tasks, it was not possible to statistically compare frequency discrimination thresholds of the two groups, as lower frequency discrimination thresholds have been found to be associated with tones of longer duration [67,68,69]

Summary

Introduction

Developmental disorders of oral and written language have been linked to deficits in the processing of auditory information. [2,3,4,5]) These theories propose a variety of different auditory processing impairments as underlying dyslexia, from deficits in ‘rapid’ auditory temporal processing [5], to frequency discrimination [6], and the detection of rate of change of amplitude at the onset (rise time) and/or during the speech envelope [2,3]. They are united in the premise that these impairments lead to difficulties in analysing the incoming speech stream and subsequent problems with phonological processing (i.e. in discriminating, categorizing, and manipulating speech sounds). A subset of these theories accounts for the oral language problems of those with specific language impairment (SLI) (e.g. [3,5])

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