The interaction of lexical and sublexical processes in reading, writing and repetition.

It has recently been proposed that in the course of repetition, reading aloud and writing to dictation, lexical representations are activated and selected for output by the joint operation of the semantic system and of sublexical conversion mechanisms--the Summation Hypothesis [Hillis and Caramazza, Brain Lang. 40, 106-144, 1991]. The hypothesis predicts that semantic errors in oral reading and in writing to dictation should only occur when both the semantic system and the sublexical component involved in that task (orthography to phonology and phonology to orthography conversion, respectively) are damaged. The performance of Italian patient E.C.A. indicates damage to the semantic system, and to sublexical phonology to phonology and phonology to orthography conversion mechanisms, but with substantial sparing of sublexical orthography to phonology conversion processes. In agreement with expectations derived from the Summation Hypothesis, E.C.A. produced semantic errors in repetition and in writing to dictation, but not in reading aloud. The paucity of semantic errors in speakers of languages with relatively transparent orthographies is discussed in the context of the Summation Hypothesis.