Phonemic restoration in developmental dyslexia

Stephanie N Del Tufo,Emily B Myers

doi:10.3389/fnins.2014.00134

Abstract

The comprehension of fluent speech in one's native language requires that listeners integrate the detailed acoustic-phonetic information available in the sound signal with linguistic knowledge. This interplay is especially apparent in the phoneme restoration effect, a phenomenon in which a missing phoneme is “restored” via the influence of top-down information from the lexicon and through bottom-up acoustic processing. Developmental dyslexia is a disorder characterized by an inability to read at the level of one's peers without any clear failure due to environmental influences. In the current study we utilized the phonemic restoration illusion paradigm to examine individual differences in phonemic restoration across a range of reading ability, from very good to dyslexic readers. Results demonstrate that restoration occurs less in those who have high scores on measures of phonological processing. Based on these results, we suggest that the processing or representation of acoustic detail may not be as reliable in poor and dyslexic readers, with the result that lexical information is more likely to override acoustic properties of the stimuli. This pattern of increased restoration could result from a failure of perceptual tuning, in which unstable representations of speech sounds result in the acceptance of non-speech sounds as speech. An additional or alternative theory is that degraded or impaired phonological processing at the speech sound level may reflect architecture that is overly plastic and consequently fails to stabilize appropriately for speech sound representations. Therefore, the inability to separate speech and noise may result as a deficit in separating noise from the acoustic signal.

Highlights

Developmental dyslexia refers to an inability to read at grade level despite adequate instruction, intellectual ability, motivation and regardless of socioeconomic status (Berninger, 2001)
Across a continuum of abilities, individuals with less intact phonological abilities may rely more on lexical-semantic information, as suggested by prior evidence from studies of individuals with phonological deficits in dyslexia (Frith and Snowling, 1983). This pattern suggests that the acousticphonetic processing or retention of acoustic-phonetic detail is not as reliable in both poor and dyslexic readers
The current findings suggest that there may be subtle deficits at the single segmental level in poor readers and individuals with dyslexia, it is noteworthy the types of tasks that are used to characterize the poor reading and dyslexic population are tasks that require subjects to combine sounds in childhood at the level of phonological processing and as adults at the whole word or pseudoword level

Summary

Introduction

Developmental dyslexia refers to an inability to read at grade level despite adequate instruction, intellectual ability, motivation and regardless of socioeconomic status (Berninger, 2001). An effort to discover a more general deficit, that culminates in spectrum of reading difficulty, has led to this population being described as having a specific reading disability (RD) (see Shaywitz and Shaywitz, 2005 for review). It is hotly debated whether this reading impairment arises from deficits in phonological awareness, rapid auditory processing, visual motion, or noise exclusion. There has been some evidence suggesting that individuals with dyslexia exhibit a more general speech perception deficit (Manis et al, 1997; Hazan, 1998)

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