Double-deficit hypothesis poses that reading disorders can be traced to deficits in phonological processing and/or naming speed. The presence of both a deficit in phonological processing and slow naming speed is predictive of the most severe reading problem. Double-deficit hypothesis likewise refers to the theory of Dyslexia which suggests that dyslexic children have biological deficits in two (2) areas: phonological processing (interpreting sounds) and in naming speed (for example, identifying letters such as b versus d, or w versus m).
Lexicon of Psychology - Terms, Treatments, Biographies,