|SPECIAL FEATURE||Vol.6 No.3 (May 2001)|
Definition of Specific Learning Disabilities:
The Hong Kong Society of Child Neurology &
Scientific Committee of the Working Party on SLD
The last 20 years has seen significant advances in the neurosciences which are pertinent to the domains of learning and education. As recently as a quarter century ago, developmental disorders that adversely affected learning were largely attributed to perinatal stress. Through recent remarkable advances in the understanding of biological underpinnings of cognition and learning, genetically determined factors in the etiology of Specific Learning Disabilities (SLD) became increasingly evident. These impinge on perceptual motor skills, reading, communication skills, written expression, mathematics and emotional components of learning. A variety of disorders which affect attention and hyperactivity may further co-exist in a significant percentage of these individuals. Neuroanatomical data at macroscopic and microscopic levels, in vivo data through functional neuroimaging and neurophysiological studies, genetic data through studies of monozygotic and dizygotic twins and linkage studies, and longitudinal research data in educational assessment and intervention based on these theoretical grounds have merged coherently towards explaining the neurobiological bases of these disorders. The co-occurrence of attentional disorders with SLD may point to an underlying shared genetic mechanism, a finding suggested by recent family studies.
Specific Learning Disabilities (SLD) is thus a generic term that refers to a heterogeneous group of disorders that covers a variety of disorders in areas of spoken and written language, mathematics, perceptual motor skills and the social and emotional components of learning. SLD is inherent in the individual and is developmental in nature. These disabilities may impact to varying degrees on all aspects of affected children's lives: at school, at home and at play. Unless given intervention appropriately, systematically and in good time, SLD may persist to adulthood. Even though SLD may co-occur concomitantly with other disabling conditions including sensory impairment, social and emotional disturbances, or external factors including cultural differences and insufficient or inappropriate instruction, they are not the result of these conditions. These factors may nevertheless, produce further adverse effects on the manifestations and prognosis of these individuals.
Among the different SLD subgroups there are varying degrees of overlap in occurrence and symptoms. The largest SLD subgroup is that of developmental dyslexia. An individual with dyslexia (difficulties with lexis or words) shows measurably below-age reading and written language development despite average or above-average intelligence, intact emotional adjustment and instruction. Such an individual shows severe difficulties in learning the script-speech sound connection (phonological processing) and the spelling/writing pattern (orthographic and morphological processing) of words to the automatic level, even though reading comprehension may be adequate. Acute disorders in individual word spelling/writing and consequently in composing also severely impede the individual's learning in both language and subject content areas.
Another common subgroup after dyslexia is that of specific language impairment. An individual with specific language impairment shows significant expressive, or receptive and expressive speech and/or language difficulties despite normal (peripheral) speech and hearing mechanisms, intelligence within normal limits, and normal emotional functioning. The impairment may be restricted to speech, or speech problems may co-occur with language, or language problems may occur on their own. Language problems can include any or all of the following: receptive delay, slow vocabulary development, word retrieval difficulties, and delayed grammatical development. Specific language impairment in preschool children can provide an early warning sign for possible later written language disorder (even if the spoken language problems have resolved).
Mathematics learning is not unitary in the cognitive processes it draws upon, and mathematics learning disabilities are multi-faceted. Individuals with mathematics learning disabilities show delayed procedural skills (such as needing to use counting to solve arithmetic problems) and in the representation or retrieval of basic arithmetical facts from long-term memory. Even when a basic fact is retrieved there tends to be a high error rate and the retrieval is unsystematic and speed poor.
The coexistence of developmental dyslexia and mathematics learning disorders in many children may reflect a more general deficiency in precise representation of symbol systems in working and semantic memory.
Specific difficulties in motor execution and/or planning are widely observed in individuals with SLD. Children with developmental coordination disorders often show inefficiencies in visual, tactile, kinesthetic and/or vestibular related motor processing. These difficulties can be manifested in either or both fine and gross motor areas such as balance, postural control and graphomotor skills.
Non-verbal learning disorders are developmental disabilities which are often observed as a cluster in some children with SLD. These individuals are motorically awkward, and characteristically weak in perceptual organization and visuospatial memory. There is poor awareness of social propriety both receptively and expressively, and although they have good vocabulary, word decoding skills and memory for verbal facts, speech is often flat and pedantic and reading comprehension impaired. Some individuals within this group may show features of a mathematics calculation disorder. The exact combination of symptoms and signs in this group is variable and subclassification of subtypes of this condition is expected. It is likely, as for other SLD, that a genetic origin underlie this condition.
Outcome studies have shown that far too many individuals with learning disabilities have unfavourable outcomes in terms of educational attainment, mental health and adult social functioning. These negative outcomes most often reflect inadequate effective help and intervention in early years. Early identification and intervention and preventive strategies against the effects of learning disabilities are hence of great priority in management. Intervention practices must in turn be supported by research in educational practices and in the biological and psychological processes that underlie learning disabilities, as well as through professional preparation that enables resulting evidence-based practices to be delivered effectively.
As the above domains are legitimate concerns of those in medicine, speech and language, occupational and physical therapy, educational and clinical psychology and of education generally. Multidisciplinary cooperation in prevention, assessment and in intervention, in close partnership with parents and families of affected individuals, is essential for minimizing the difficulties and in promoting the opportunity for success in helping these persons.