Original sentence: The modal approach has been to search for invariant cues that have somehow been missed -- that is, to hypothesize that there is no lack of invariance problem aside from the fact that researchers have not discovered how to detect invariant cues available to listeners
Edited sentence: The modal approach has been to search for invariant cues that have somehow been missed—that is, to hypothesize that there is no lack of invariance problem aside from the fact that researchers have not discovered how to detect invariant cues available to listeners