The ability to read is believed to depend on two skills.

Phonological processing skills make up the ability to identify and manipulate sounds in speech.

Automatic naming skills compose the ability to translate visual information into a phonological code.

The double-deficit theory of reading disability (Wolf & Bowers 1999) proposes that a deficit in both these skills gives rise to the lowest level of reading performances, known as dyslexia.

References

Wolf, M., & Bowers, P. (1999). The "Double-Deficit Hypothesis" for the developmental dyslexias. Journal of Educational Psychology, 91, 1-24.