I think the morphemic shift you are referring to is the way in which stress shifts from one morpheme to another in different derivations. Thus, in photograph
and its derivatives the stress shifts back and forth between the first morpheme, phot
, and the second, graph
, the o
being a non-morphemic linking particle. For instance, in photograph
there is primary stress on the first morpheme and secondary stress on the second with no stress on the particle. But in the word photographer
neither of the morphemes is stressed, the primary stress now falling on the linking particle o
. And in photographic
the the first morpheme has secondary stress, and the second has primary stress, the particle again being unstressed.
If this is not the issue you were asking about, let me know, and Ill try again.