I read something similar once I Googled it after I made my first post, so my use of stammer can be misleading for some I guess. Though some sources I read specifically mentioned a stammer as the blocking of words, so I can't say for sure. As an American, since most people call any kind of speech impediment a stutter (and usually referring to the repetition of words), using stammer makes the distinction that it's something similar but different. A more universal term could be just "silent blocks", but it could be confusing for people who don't know much about speech impediments.