One problem, raised by Alfonso Caramazza in the form of a question after a talk I gave, is that sometimes conduction aphasics get stuck on the simplest of words. Case in point, in my talk, I showed an example of such an aphasic who was trying to come up with the word cup. He showed the typical conduit d'approche, "its a tup, no it isn't... it's a top... no..." etc. Alfonso justifiably noted that conduction aphasics shouldn't have trouble with such simple words if the damaged sensory-motor circuit wasn't needed as critically in these cases.
My suggestion in the previous post was that this may be explained in terms of a difference in the processes involved in naming versus repetition. I further speculated that part of the problem might be related to neighborhood density issues. Several very interesting and useful comments on that post, e.g., by Matt Goldrick, convinced me that my idea may not be all that solid.
Ok, enough back story. Here is another possible solution to the problem raised by Alfonso. It is actually one that I used to discuss in my talks, and may have even written about in print, but (duh) I seemed to have forgotten it until now (getting older sucks):
It seems likely that the lesion/deficit in conduction aphasia is not restricted to the sensory-motor network (i.e., area Spt), but also involves phonological processing/representation systems in the STG/STS. The lesions clearly involve these regions:
patients with conduction aphasia generally had more posterior lesion that overlapped in the superior temporal gyrus and inferior parietal cortex (Baldo et al., 2008, Brain and Language, 105, 134-140).
So perhaps the naming deficit in at least some conduction aphasics reflects damage to phonological systems in the left hemisphere (in addition to the load-dependent deficits caused by damage to Spt). The idea is that partial damage to phonological systems in the left hemisphere will disrupt phonological access during naming (which is harder and may be left dominant) more than recognition (which is easier and more bilaterally organized).