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Front Hum Neurosci. 2014 Jun 24;8:460. doi: 10.3389/fnhum.2014.00460. eCollection 2014.

Magnocellular-dorsal pathway and sub-lexical route in developmental dyslexia.

Author information

1
Developmental and Cognitive Neuroscience Laboratory, Dipartimento di Psicologia Generale, Università degli Studi di Padova Padova, Italy ; Developmental Neuropsychology Unit, Istituto Scientifico "E. Medea" di Bosisio Parini Lecco, Italy.
2
Ophthalmological Unit, Istituto Scientifico "E. Medea" di San Vito al Tagliamento Pordenone, Italy.
3
Developmental Neuropsychology Unit, Istituto Scientifico "E. Medea" di Bosisio Parini Lecco, Italy.

Abstract

Although developmental dyslexia (DD) is frequently associate with a phonological deficit, the underlying neurobiological cause remains undetermined. Recently, a new model, called "temporal sampling framework" (TSF), provided an innovative prospect in the DD study. TSF suggests that deficits in syllabic perception at a specific temporal frequencies are the critical basis for the poor reading performance in DD. This approach was presented as a possible neurobiological substrate of the phonological deficit of DD but the TSF can also easily be applied to the visual modality deficits. The deficit in the magnocellular-dorsal (M-D) pathway - often found in individuals with DD - fits well with a temporal oscillatory deficit specifically related to this visual pathway. This study investigated the visual M-D and parvocellular-ventral (P-V) pathways in dyslexic and in chronological age and IQ-matched normally reading children by measuring temporal (frequency doubling illusion) and static stimuli sensitivity, respectively. A specific deficit in M-D temporal oscillation was found. Importantly, the M-D deficit was selectively shown in poor phonological decoders. M-D deficit appears to be frequent because 75% of poor pseudo-word readers were at least 1 SD below the mean of the controls. Finally, a replication study by using a new group of poor phonological decoders and reading level controls suggested a crucial role of M-D deficit in DD. These results showed that a M-D deficit might impair the sub-lexical mechanisms that are critical for reading development. The possible link between these findings and TSF is discussed.

KEYWORDS:

dorsal stream; phonological decoding; reading acquisition; reading disability; transient system; visual disorder

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