ABSTRACT
In this chapter, I focus on two issues: (1) What is the causal relation between problems in verbal STM, including problems in phonological coding
Typically, discussions of the causal relation between verbal STM problems and dyslexia focus on two alternatives: Such problems are either a cause or a result of dyslexia. Given these two alternatives, one need only provide longitudinal evidence showing that verbal STM problems precede the onset of dyslexia to argue against such problems being merely a result of dyslexia. However, we feel that addressing this issue first requires a careful conceptual analysis of what the possible relations are between a symptom (e.g., verbal STM problems) and a disorder (e.g., dyslexia) with which it is associated. Following Ehri (1979), we can distinguish at least four possibilities: (1) VSTM problems are a prerequisite for dyslexia (a primary symptom); (2) VSTM problems are a facilitator of dyslexia (a contributing symptom); (3) VSTM problems are a consequence of dyslexia (a secondary symptom); (4) VSTM problems are a correlate of the prerequisite deficit (a correlated symptom). To this list we can add two other possibilities: (5) The symptom is both a prerequisite for and a consequence of the disorder (reciprocal causation); (6) the symptom is artifactually related to the disorder (artifactual symptom).
