For many years, research on individual differences was plagued by the failure to carry out thorough process analyses on the experimental tasks employed. Thus, it was rarely possible to ascribe any cognitive specificity to an observed group difference. This problem has partially been alleviated due to the general influence of a paradigmatic assumption of cognitive psychology: that performance on any single task is the result of the simultaneous or successive operation of many different information-processing operations. However, it took a long time for reading disability researchers to accept an implication of this assumption: that one could not merely observe a difference on, for example, a perceptual task, and then announce that "visual processing" was the key to reading failure, based on one's introspection about what the task tapped. It was sometimes hard to understand that no matter how large the performance difference observed on a single task, such an outcome represented not the end, but instead the beginning of a careful task analysis that one hoped would reveal the cognitive locus of the difference. The rise and fall of many of the popular hypotheses in the dyslexia literature mirrors this belated realization (see Vellutino, 1979).
Paring Down the Number of Causal Relationships
It will be argued here that these bootstrapping effects of reading experience and other secondary effects have been inadequately considered in the extensive literature on individual differences in the cognitive processes of reading. Although it might seem that a consideration of the effects of these reciprocal relationships would complicate our models, it actually has great potential to clarify reading theory. If only a few of these reciprocal effects control a large portion of the variance in reading ability, we will be able to exercise parsimony elsewhere. Such a consideration will