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This work was supported by grants from the National Institute of Child Health and Human Development (P50 HD25802, RO1 HD046171, R01 HD057655).
No doubt since humans first began to read, there have been those who struggled with the printed word. The seeming ease with which most children learn to read contrasts sharply with the travails of a surprisingly large subgroup of children as they try to extract meaning from print. How we read and why some very bright children and adults struggle to read has intrigued and challenged generations of investigators. More recently, particularly with the advent of the powerful tools of modern neuroscience, the very act of reading has become visible. The ability to image reading (and dyslexia) has provided a neurobiological framework within which to incorporate advances in cognitive psychology, developmental psychology, linguistics, neurology, genetics, epidemiology, and education to provide an increasingly specified and fine-grained account of reading and dyslexia. The perspectives gained from such a multilevel integration, particularly emerging insights into the role of attentional processes in deciphering the code, suggest new avenues of scientific exploration and perhaps newer therapeutic targets and strategies to improving reading. We first consider how children learn to read and why reading is much more difficult than speaking.
How We Read
Although print emerged from, and maintains its roots in, the language system, the differences between written and spoken language provide an account of why reading is difficult and speaking is easy. This relationship between spoken and written language is perhaps best captured by the statement, "Writing is not language, but merely a way of recording [spoken] language by visible marks" (Bloomfield, 1933, p. 21). A number of theories of dyslexia have been proposed, including phonological theory (Liberman, Shankweiler, & Liberman, 1989; Ramus et al., 2003), rapid auditory processing theory (Tallal, 1980, 2000; Tallal, Miller, & Fitch, 1993), visual theory (Livingstone, Rosen, Drislane, & Galaburda, 1991; Lovegrove, Bowling, Badcock, & Blackwood, 1980), cerebellar theory (Nicolson & Fawcett, 1990; Nicolson, Fawcett, & Dean, 2001), and magnocellular theory (Galaburda, Menard, & Rosen, 1994; Livingstone et al., 1991; Stein, 2003; Stein & Walsh, 1997). Ramus et al. (2003) provide a review and critique of the various theories. Of the several theories suggested, an explanation reflecting what is known about the...