Reading errors following right hemisphere injection of sodium amobarbital

The role of the nondominant hemisphere in reading is controversial. We characterized the reading errors made by 64 right-handed adults with complex partial seizures (half with seizure foci on the right and half on the left), after right hemisphere injection of sodium amobarbital. Subjects were presented with 20 six-word sentences and all were found to have speech associated with the left hemisphere only. A variety of reading errors occurred, most of which fell under the syndrome of "neglect dyslexia" including deletions and substitutions of whole words on the left side of a line of text as well as within-word neglect errors. The nature of these errors indicated that they may have been caused by an interaction between a peripheral processing deficit and more centrally located conceptual knowledge of linguistic structure. Other errors could be attributed to a general decrease in attentional mechanisms. Neglect errors at the level of the sentence occurred in the absence of neglect errors at the level of the word although the converse was not true. This suggests that the latter may represent a more severe deficit in the mechanism that causes the former. A double dissociation existed between single word neglect dyslexia errors and "visual" errors, indicating separate processing mechanisms.