||Vol.6 No.3 (May 2001)
Dyslexia and other Specific Learning Disabilities
Dr. Catherine Lam
Child Assessment Service, Hong Kong
Dyslexia and other specific learning disabilities are still not universally
recognized as conditions that cause difficulties in children's learning. Indeed
they have been often referred to as "hidden handicaps" because of
the lack of awareness by teachers, physicians and parents. There is also the
erroneous belief by many that these are rare and mild problems despite evidence
to the contrary. Attempts to achieve a universally accepted definition for specific
learning disabilities have been plagued by continuing and often bitter disagreements
among the various professions who have legitimate interest in this field. These
disciplines include neuroscience, neurology, clinical and neuropsychology, education
professions including educational psychology, teaching and education administration,
speech and language pathology and so on. This fragmentation arises from differences
in focus by individual professions on the various aspects of specific learning
disabilities, with each discipline often not being aware of practices and advances
in other fields. Territorial interests add to the poor communication. Finally,
differences in identification criteria for subjects often make sharing of research
data across professions all but totally meaningless.
"Specific Learning Disabilities" (sometimes referred to as "Specific
Learning Difficulties" in the United Kingdom and "Learning Disabilities"
in the United States) is a generic term which here refers to a group of learning
disorders with respective cognitive specific deficits. Prevailing evidence based
upon sound theories as well as replicable, valid prospective longitudinal studies,
indicate that specific learning disabilities involve the following features.
- A heterogenous group of disorders of constitutional origin,
- Specific psychological process deficits causing impairment in corresponding
domains of learning. Major forms include dyslexia, specific disability in
oral language, specific disabilities in mathematics and non-verbal learning
- These disabilities may occur alone or co-occur in various combinations.
- Specific learning disabilities often exist in spite of adequate intelligence,
normal sensory and motor apparatus, and adequate educational opportunity;
but could occur concomitantly with other handicapping conditions (sensory
impairment, mental impairment, social and emotional disturbance) or extrinsic
influences (cultural differences, insufficient or inappropriate instruction),
although they are not the result of these conditions.
- While problems such as attention deficit disorder are not specific learning
disabilities in themselves, they may exist as comorbid conditions in an individual
with specific learning disabilities.
Non-validated general definitions are unfortunately still being used despite
extensive research evidence which support the above understanding of specific
learning disabilities. These include:
- "Exclusionary Criteria": These define an individual with specific learning
disabilities as one who demonstrates difficulties in learning despite "not
being mentally retarded, not suffering from sensory handicaps, not being emotionally
or socially deprived" etc. Such a definition is not helpful in delineating
what the nature of the disorder is. It results in a group of extremely varied
conditions, and cannot contribute to specific intervention prescription nor
- "IQ-Achievement Discrepancy Criteria": Increasing evidence points to the
lack of validity of the IQ-discrepancy as an identifier of specific learning
deficits. A specific disability such as dyslexia, for example, could only
be identified through detection of the corresponding specific process deficit.
- "Operational Definitions": These may define an individual with specific
learning disabilities as one who performs in specified domains below a certain
percentile standard, or who demonstrates a certain grade level lag in those
areas. They are often used in education policy for resource gate keeping,
and bear limited relation to theoretical considerations.
Definition of Dyslexia
- Dyslexia is one of the most prevalent types of specific learning disabilities.
It is a developmental language based disorder which affects an individual's
ability to acquire skills for individual word reading (i.e. word recognition).
Problems with automatic retrieval of words are also present, hence the difficulty
with dictation and spelling.
- Dyslexia is a constitutional disorder, hence it is lifelong and often occurs
in families. It is not an all-or-nothing phenomenon but occurs in degrees
similar to other biological disorders, so manifestation occurs in a continuum.
- Prognosis depends on the severity of the disorder, the specific pattern
of other strengths and weaknesses within the individual, and the availability
and appropriateness of intervention.
- Difficulties with receptive and expressive oral language often co-exist.
- Difficulties with writing (i.e. handwriting), a visuomotor impairment,
is not a feature of dyslexia itself although they could co-exist in an individual.
- Literature quotes an average of 10-20% of children being affected with
specific reading difficulties, with around 5% being severely affected. This
would mean that 2 children per class of 40 students may be significantly affected!
Contributory Etiological Bases for Dyslexia
- Dyslexia is believed to be due to a central nervous system dysfunction
leading to a core deficit in reading because of a failure to rapidly, accurately
and automatically recognition and recall individual written words. Such individual-word
recognition difficulties are in turn obvious obstacles to understanding what
is being communicated in a sentence, paragraph or passage.
- Substantial evidence is available to support the role of deficient phonological
(speech sound) processing as the major cause of this disability.
- Simultaneous efficient processing of the sound of a word, efficient analysis
of its appearance (orthographic analysis), and access to its meaning are necessary
to allow skilled word recognition and fluent reading. This language based
ability is deficient in individuals with dyslexia.
Genetic, neuroanatomical, neurophysiological and neuobiological features have
been identified in dyslexic individuals.
- Genetic Findings
Large longitudinal twin studies have shown that consitutional factors of genetic
origin are involved in dyslexia. Both major gene form and polygenic modes
of transmission are supported. In some families genetic markers on chromosome
15 have been detected, and chromosome 6 is possibly implicated in other families.
- Neuroroantomical Features
The left planum temporale on the superior temporal lobe of the brain is believed
to be responsible for language processing in the majority of people. In dyslexic
individuals, ectopia and heterotopias within the left perisylvian cortical
area were detected, and the usual asymmetry between the left and right brains
were absent. The relationship between planum temporale morphology, language
and psycholinguistic function is significant in understanding the etiology
- Neurophysiological Features
Studies in brain electrical activity mapping recordings distinguished between
dyslexic and non-dyslexic individuals, with aberrant physiology found in cortical
areas usually involved in speech and reading in dyslexic individuals. Positron
emission tomography (PET) scanning showed functional alterations in dyslexia
adults during the act of reading, and Xenon-133 photon emission computed tomography
(SPECT) indicated decreased regional cerebral flow (rCBF) in left prefrontal
and perisylvian regions in children with developmental language learning disabilities.
- Neurobiologiccal Features
Most recently, fMRI studies of the neurobiology of reading in dyslexic and
non-dyslexic children and adults have suggested a tentative neural architecture
for word reading involving a) the extrastriate cortex within the occipital
lobe in identification of letters, b) the inferior frontal gyrus in phonological
processing, and c) the middle and superior temporal gyri in accessing meaning.
Gender difference in brain representation for phonological processing have
provided explanation why women are less likely than men to suffer significant
impairments in their language skills after a stroke and tend more often to
compensate for dyslexia, despite an equal gender incidence of the condition.
The identification of unique brain activation patterns in individuals promises
more precise diagnosis of dyslexia and may allow access to the effects of
Other Types of Specific Learning Disabilities
Specific Learning Disability in Spoken Language
Specific language impairment occur in individuals who exhibit linguistic
deficits which outwardly appear subtle. These deficits affect different
aspects of linguistic performance, including phonology (speech sounds),
semantics (meaning), grammar and so on, presenting as expressive language
and comprehension disorders which affect academic achievement and social
Specific Learning Disability in Mathematics
Impairment in ability to learn mathematics may result from a variety of
deficits: linear thinking and rapid recall of learned facts such as those
required in mechanical arithmetic; linguistic analysis of problems in mathematical
reasoning; visual-spatial abilities for comprehension of many mathematical
concepts, and problem solving skills for complex mathematical tasks.
Non-Verbal Learning Disabilities
Motor Planning and Coordination Disorders
Individuals with motor planning and coordination problems have difficulties
in gross and fine motor execution, in postural control and balance,
in graphomotor skills (i.e. controlling pencil and paper during writing),
and are commonly described as "clumsy".
Visual Spatial Organization and Perceptual Disorders
These individuals have difficulty in understanding spatial relations,
left/right concepts, and in perceptual organization of nonverbal output
(including for drawing and handwriting).
Dyslexia and other specific learning disabilities bring with them many secondary
problems. With good intellectual potential, these individuals' discrepantly
low attainment in one or more scholastic areas cause perplexity and misunderstanding.
The following are some common sequelae.
- Increasing amounts of time are spent on homework with progressive restriction
of extra-curricular and social activities and its ensuing problems.
- Deterioration of relationship between child and parents (typically the
mother, who supervises homework), and frequent increase in strife between
parents on how school demands and failures should be dealt with.
- Teachers often complain that the affected child who appears normally intelligent
is being lazy or oppositional, and the child may be stigmatized as such by
the school and classmates.
- These children's self esteem gradually becomes eroded, secondary emotional
and behavioural problems arise, and many may drop out of school - either literally
or in spirit - and later end up as problematic young people and unemployed
Non-validated Beliefs about Dyslexia and Specific Learning Disabilities
- Misconception that dyslexia is a writing problem manifesting as mirror
writing and reversals due to visual perceptual problems. Dyslexia is a language
based disorder due to constitutional differences in the brain area which subserves
- Non-validated belief that Chinese characters, being "picture-like", is
interpreted through visual-spatial processes, and that the right hemisphere
of the brain is more involved in reading Chinese than alphabetic languages.
Research evidence indicates that Chinese reading draws on linguistic skills
in the same way does English, and that the above assumptions are to date not
- Misconception that individuals will "grow out of dyslexia. Being a constitutional
difference dyslexia persists in an individual who may, however, compensate
successfully in life. Dyslexics who are more severely affected or who are
not given appropriate intervention may be permanently handicapped.
- Misconceptions about the intellectual potential of dyslexic individuals.
Being dyslexic neither implies that the individual is "retarded" nor that
he must have special talents and superior intelligence.
- Misconception that dyslexic individuals cannot read well because of eye
problems such as impaired ocular movement or abnormal sensitivity to glare
or certain colour frequencies. These problems may lead to inefficiency or
strain during text reading, but do not cause a single word learning linguistic
disorder as in dyslexia.
Non-Validated or Controversial Treatment Approaches
The following controversial therapies are either found not to have proven value,
to be misapplied, or in some cases to be groundless in their claims towards
treatment of dyslexia or other specific learning disabilities.
- Optometric therapy for dyslexia, including vision training, prism or coloured
lenses. Ocular movement disorders, light sensitivity etc. should be managed
as such and not as causes of word recognition deficits.
- Auditory Integration Training for learning and other developmental disabilities.
- Sensory integration therapy for dyslexia. Sensori-motor training may be
appropriate for certain types of motor planning and coordination related learning
- Medications for dyslexia. These include herbs, trace elements and psychotropic
drugs, often with the claim that they target its basic pathophysiology. Medications
which improve attention control are sometimes added in polypharmacy, and may
cause change in behaviour which is reported as "improvement in the dyslexic
- Neurophysiological therapies for learning and emotional disorders. There
is claim that such therapy may help to "reset" brain waves.
The Paediatrian's Role
- History taking should include perinatal and developmental information,
in particular on language development, motor development and behaviour.
- Family history of dyslexia and other specific learning disabilities should
be specifically asked for.
- Examinations include general and elemental neurological evaluation, together
with hearing and visual function assessments.
- Evaluation of learning difficulties by the neurodevelopmental paediatrician
should include a detailed history of observations by parents and teachers
on the child's learning, a careful review of the child's recent school work
to search for clues on the nature of his problems, and an extended neurologic
examination which taps sensori-motor and cognitive processes as well as behavioural
features that affect learning .
- The neurodevelopmental paediatrician should be able to prescribe the involvement
of relevant multidisciplinary team members, and to understand the significance
their findings. Members include the clinical psychologist (preferably one
with experience in paediatric neuropsychology), speech and language pathologist,
occupational and physical therapists, optometrist and medical social worker.
- Explanation of findings and counselling should be provided by the paediatrician
to the parents and when appropriate to the child.
- The paediatrician should lead team coordination in providing relevant therapy
or interim support for the child and parents.
- He should ensure that arrangements for further management by educational
professionals are effected, including by educational psychologists, teachers
and if available, special educational needs teachers. Review sessions should
be scheduled as appropriate.
- Not least, the paediatrician should be ready to act as the child's advocate.
Principles of Management
- Management of dyslexia and other specific learning disabilities begins
with accurate identification and characterization of the deficits and of other
strengths and weaknesses of the child. Evaluation of the support which he
may receive from parents and school are also essential.
- Intervention for dyslexia and other specific learning disabilities should
- a. Direct teaching and remediation for the specific deficit(s).
- b. Accommodations in school so that the child may circumvent his handicap
and continue to learn as other children: e.g. having examination questions
given and answered orally for a dyslexic child.
- c. Allowances in tasks where he needs to overcome his disability: e.g.
less copying tasks for a child who has graphomotor output difficulties.
- The above measures should be available in adequate amounts and throughout
the child's learning years. Short, one-off instructional courses to the child
or parents will not suffice. Interim reassessment of intervention efficacy
should be carried out, and modification of strategies made along the way as
- Finally, it is not the substance of the education which needs to be changed
for these children (unlike for example, educational targets for mentally retarded
children which need to be lowered), but the process through which these educational
goals are achieved which need to be specifically and professionally adapted.
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