Learning Disabilities

UNDER CONSTRUCTION

Developmental studies suggest that two distinct procedures
are implicated in the development of the reading system.
When learning to read, a child initially builds up a sight
vocabulary of familiar words where mappings are formed
between visual patterns of written words and their
pronunciations. Words with irregular sound-to-spelling
correspondences can only be read via this strategy, known
as the lexical procedure. However, to be able to decode the
many new words encountered when learning to read, the
child must develop an alternative reading strategy, based on
the component letters of the word and the corresponding
letter sounds. This phonological strategy operates at a
subword level, first by segmenting any unfamiliar written
word into its individual letters or letter segments
(graphemes) and then by blending together the
corresponding speech sounds (phonemes).

Many children experience difficulties in acquiring the
phonological strategy of reading. These difficulties are
thought to arise from a deficit in the awareness of the
phonological structure of words, which prevent learning of
letter-to-sound correspondences needed for phonological
reading. Recent studies of brain function have highlighted
abnormalities in the neural mechanisms underlying
phonological treatment in individuals with phonological
dyslexia. Adults and children with dyslexia show decreased
activity in the left temporal cortex, as well as significant
overactivation of the left inferior frontal region during
phonological processing. Such abnormal neural responses
have been observed in a number of studies, using different
methodologies, such as PET and fMRI techniques, and
across multiple tasks (e.g., rhyming, nonword vs word
reading, and explicit and implicit reading)]. These findings
strongly suggest an implication of both temporal and frontal
lobes in the phonological processing of reading.