It has recently been proposed that in the course of repetition, readin
g aloud and writing to dictation, lexical representations are activate
d and selected for output by the joint operation of the semantic syste
m and of sublexical conversion mechanisms-the Summation Hypothesis [HI
LLIS and CARAMAZZA, Brain Lang. 40, 106-144, 1991]. The hypothesis pre
dicts that semantic errors in oral reading and in writing to dictation
should only occur when both the semantic system and the sublexical co
mponent 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 con
version mechanisms, but with substantial sparing of sublexical orthogr
aphy to phonology conversion processes. In agreement with expectations
derived from the Summation Hypothesis, E.C.A. produced semantic error
s in repetition and in writing to dictation, but not in reading aloud.
The paucity of semantic errors in speakers of languages with relative
ly transparent orthographies is discussed in the context of the Summat
ion Hypothesis.