Deficit or Delay: Neuropsychological Models of Developmental Dyslexia

Abstract

This review examines issues and research relating to the involvement of the central nervous system in reading disorders. Questions regarding subtypes, pre-and perinatal influences, genetics, sex differences, and early identification are briefly surveyed along with a summary of major research findings in neuropsychology and neurology. Particular attention is devoted to the assessment of the brain-deficit model vis-à-vis the maturational-lag model of developmental dyslexia. Neither theory can adequately account for the entire population of dyslexics. For progress to be made in this area, attention must be focused on theory articulation and reformulation in addition to methodological and taxonomic advances. Specific reading disorders in children are often thought to reflect abnormalities in the central nervous system. The term developmental dyslexia is typically applied to children with reading problems after other factors -such as emotional disturbance, environmental deprivation, inadequate teaching, and sensory impairment -have been dismissed as causal agents. This indirect means of classification is strewn with sources of error. For example, Roswell and Natchez (1977) noted that rarely can emotional difficulties be isolated in order to determine precisely how they interfere with learning. One has to confront the question of whether emotional problems are the cause or product of reading failure. Difficulty is also encountered with other items in the exclusion clause: What constitutes environmental deprivation, inadequate teaching, or even sensory impairment? While it is important to examine all elements which could potentially contribute to reading disabilities, it must be emphasized that they rarely appear alone. If research is to explore the role of the brain in relation to reading disabilities, criteria that are directly relevant to this association must be studied. Concurrent review of other factors may lead to useful information regarding interrelationships. Unfortunately, the criteria to define dyslexia by inclusion alone are not yet available, and clinicians along with researchers have had to be content with ruling out factors such as emotional problems or environmental disadvantage as prirrcary causal factors.The purpose of this article is to examine research findings on the role of the brain in developmental dyslexia. Of particular importance will be an evaluation of the theoretical models advanced to elucidate this relationship. The deficit model proposes that there is a cerebral dysfunction underlying the inability to acquire appropriate reading skills. Descriptions or speculations on the nature

Comorbidity between mathematics and spelling difficulties

“…Thomson's study (50) showed that pupils suffering from dyslexia had poor knowledge of tables, and found it difficult to carry out the four basic mathematical operations. Other researchers have interpreted observed comorbidity in the light of dysfunction of the short-term memory and/or long-term memory (7,17,26,54), or of weak functional skills in phonemic analysis (e.g., (6,13)). …”

Long-Term Follow-up Studies of Learning-Disabled Persons

“…Several investigators have proposed such subgroupings of LD persons (Dalby, 1979;Doehring, Hoshko & Bryans, 1979;Fisk & Rourke, 1979;Rourke & Orr, 1977;Rymantas & Rourke, 1979). Nevertheless, few followup studies have identified meaningful subgroup distinctions in their LD samples in order to determine differential outcomes.…”

The Neurobiological and Neuropsychological Foundations of Learning Disabilities

“…Dichotic listening and visual half-field techniques have been used primarily to investigate this hemispheric organization. Although these research techniques have accounted for most of the experimental behavioral methodology, other methods such as hemispheric time-sharing (Dalby & Gibson, 1981;Hiscock & Kinsbourne, 1978;Obrzut, Hynd, Obrzut, & Leitgeb, 1980) and monitoring of manual gestures (Kimura, 1973) also have been employed as techniques to examine lateralization of language (Dalby, 1979).…”