2.7 Reflecting on explanations of ‘abnormal’ development: the case of dyslexia
We can draw the following general conclusions about cognitive and biological explanations of abnormality from the material presented above.
Both cognitive and biological accounts of dyslexia are offered as theories which explain the behavioural difficulties that are observed. While some theories may dominate accounts of a given condition (e.g. the phonological deficit hypothesis), and may result in influencing the nature of interventions, they are still only theories and always need to be validated by consistent empirical evidence.
Any single level of description, taken in isolation, will provide an incomplete account of what may cause the behavioural symptoms. Evidence and theories from different levels of description give a fuller account of a condition and better reflect the systemic nature of dyslexia.
Research evidence provided at one level of description can support a theoretical idea offered at a different level. For example, the evidence suggesting that people with dyslexia show neurological abnormalities in the magnocellular visual pathway (biological evidence) lends support to the visual deficit hypothesis (cognitive explanation).
The case of dyslexia illustrates a general finding that few conditions are caused by a single biological problem, which affects a single cognitive process, which in turn results in a consistent set of behavioural symptoms. Within most conditions there will be a good deal of potential variability in the symptoms manifested, the cognitive processes affected and the biological factors proposed to explain them. This is because human behaviour is the product of the complex interplay between cognitive and other processes, influenced by a whole range of interconnected and modifiable biological systems. Our ‘environment’ (physical, psychological and biological) can impact on all these levels and either exacerbate or temper the severity of the condition as a result.
Summary of Section 2
Theoretical explanations of ‘abnormal’ development conditions need to take into account behavioural, biological, cognitive and environmental evidence.
Cognitive explanations of dyslexia include deficits in phonological awareness, visual perception and automatisation of skills.
Biological explanations of dyslexia refer to observed abnormalities in brain architecture, perceptual pathways and biochemistry.
External environmental explanations are specifically excluded from current definitions of dyslexia. However, evidence suggests that certain home and school environments can contribute to successful reading development.