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A temporal sampling framework for developmental dyslexia

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Neural coding by brain oscillations is a major focus in neuroscience, with important implications for dyslexia research. Here, I argue that an oscillatory ‘temporal sampling’ framework enables diverse data from developmental dyslexia to be drawn into an integrated theoretical framework. The core deficit in dyslexia is phonological. Temporal sampling of speech by neuroelectric oscillations that encode incoming information at different frequencies could explain the perceptual and phonological difficulties with syllables, rhymes and phonemes found in individuals with dyslexia. A conceptual framework based on oscillations that entrain to sensory input also has implications for other sensory theories of dyslexia, offering opportunities for integrating a diverse and confusing experimental literature.

Section snippets

Dyslexia and auditory neuroscience

Developmental dyslexia affects ∼7% of children and is defined as a specific learning difficulty affecting reading and spelling that is not due to low intelligence, poor educational opportunities or overt sensory or neurological damage [1]. Across languages, children with dyslexia have poor phonological processing skills, leading to the dominant phonological core deficit [2] model of this heterogeneous disorder. Here, I propose a novel causal framework for developmental dyslexia, the temporal

The temporal sampling framework

Although current phonological models of dyslexia are based on deficits in subsyllabic phonology (e.g. awareness of onset-rimes and phonemes, see Glossary), developmental dyslexia also involves impaired syllabic and prosodic perception [17] (Table 1). A general difficulty in distinguishing different modulation frequency ranges, which particularly affects the slower temporal rate in speech processing and tracking of the AE, would affect the efficiency of syllabic segmentation. Rise times are

A developmental perspective

As both dyslexia and SLI are developmental disorders of learning, the phonological deficits in these disorders, according to the TSF, must arise because basic auditory processing is atypical from birth. Indeed, human infants show syllabic sensitivity as neonates [29], using rhythmic cues to segment syllables and words from the acoustic signal to build a lexicon of spoken word forms. Deficiencies in processing low-frequency modulations in infancy would reduce rhythmic sensitivity and impair

Predictions from the TSF

The TSF makes several novel predictions about sensory, cognitive and behavioural deficits in dyslexia, some of which have been previously been explored and some of which can be evaluated using data from other research perspectives [22]. In particular, the postulated rise-time deficits can explain a host of seemingly disparate perceptual and linguistic deficits. For example, rise time is a crucial cue to the perception of syllable stress and also to rhythmic timing [42]; therefore, both should

The temporal sampling framework and other sensory theories

As noted earlier, there are many sensory deficits in dyslexia (see Table 1 for examples). Theories of attention difficulties in dyslexia [37] fit the TSF, as attention is enhanced when stimuli arrive in phase with neural oscillations [26]. Impaired phase locking in dyslexia could explain the atypical visual and auditory cueing effects that underpin sluggish attention-shifting theory [37]. Theories based on magnocellular dysfunction [35] have suffered from inconsistent data [56]. Researchers now

Concluding remarks

The TSF proposes a specific deficit in dyslexia with low-frequency phase locking mechanisms in auditory cortex, which is argued to have an impact on phonological development. The proposed auditory phase locking deficit might also have implications for the efficient functioning of other sensory systems. Being able to define the core neural deficit(s) underlying dyslexia will improve the efficacy of educational interventions. The TSF suggests a novel focus on the syllable in educational

Acknowledgements

I thank David Poeppel, Steven Greenberg and Ian Winter for many helpful discussions during the development of this framework, and Vicky Leong, Denes Szücs and Martina Huss for their comments. U.G. is supported by a Major Research Fellowship from the Leverhulme Trust and funding from the Medical Research Council (G0400574).

Glossary

Allophone
acoustically different forms of the same phoneme; for example, the sound corresponding to the letter P in the spoken syllables ‘spin’ and ‘pin’ is acoustically different, the sound in ‘spin’ being more like /b/, but both sounds are treated in English as the phoneme /p/.
Amplitude
volume of sound (intensity).
Amplitude envelope (AE)
the summation over time of the intensity fluctuations (amplitude modulations) in the different frequency channels in the speech signal.
Formant
a concentration of

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