The characterization of dyslexia as a language learning impairment can be traced back to Samuel Orton who in 1937 wrote that ‘strephosymbolia’ (his term for the condition) was due to an impairment of the ‘language faculty’. Some 40 years later, Vellutino (Theory and research, 1979) published his classic text, Dyslexia: Theory and Research in which he argued that dyslexia could be characterized as a verbal processing deficit. However, in more recent times, the language difficulties of dyslexia have been underplayed Adlof et al. (Language, speech, and hearing services in schools, 49(4):762-773, 2018). First, the discrepancy definition of dyslexia considers it a specific learning disability ‘diagnosed ’ when reading skills are below expectation given IQ, typically ruling out children with lower verbal abilities (Snowling et al., 2020). Second, the phonological deficit hypothesis states that phonological (speech) processing skills are impaired in dyslexia, regardless of IQ Stanovich et al. (In Perspectives on the classification of specific developmental disorders :105-136, 1998) and hence often despite good oral abilities. Within these views, dyslexia is a disorder of written language distinct from developmental language disorder (DLD) in which spoken language skills are impaired. In this paper we take a close look at the similarities and differences between dyslexia with and without DLD and discuss their shared cognitive risk factors, drawing out implications for assessment and intervention.
