Psychologists Denis Pelli and Katharine Tillman have shown that reading is a team effort in the sense that the three reading processes of letter decoding, whole world recognition, and using sentence context, each make a unique, additive contribution to reading speed.
Eleven participants read passages from the mystery novel Loves Music, Loves to Dance by Mary Higgins Clark. The researchers knocked out the contribution of the three reading processes, one at a time, or in combination, by manipulating the text, and observed the effect this had on reading speed. This is the first time all three processes have been studied at once in this way.
To knock out sentence context, they changed word order (e.g. “Contribute others. The of Reading measured”). To knock out whole word recognition, they alternated capital and lower case (e.g. “ThIs tExT AlTeRnAtEs iN CaSe”). And to knock out letter-by-letter decoding, they substituted letters in such a way that word shape was maintained (e.g. “Reading” becomes “Pcedirg”).
Letter decoding was found to account for 62 per cent of reading speed; whole word recognition 16 per cent; and sentence context 22 per cent. Crucially, while the influence of the different processes was additive, there was no redundancy. So when letter decoding was knocked out, the contribution of the other processes to reading rate didn't increase. That is, the three processes don't work on the same words. Speed reading proponents will be interested to note that among the faster readers, predicting words from sentence context made a bigger contribution to reading speed than among the slower readers.
“That letters, words and sentences are all involved in reading is nothing new, but finding that their contributions to reading rate is additive is startling” the researchers said.
Pelli, D.G. & Tillman, K.A. (2007). Parts, wholes, and context in reading: A triple dissociation. PloS one, 8, e680. (Open access).
Link to speed reading discussion in Slate.