subvocalization
Noun
Meaning
(uncountable) The formation in thought of words or statements, which are expressed inwardly but not uttered aloud.
(countable) Subvocal words or statements so formed.
Source: en.wiktionary.orgExamples
It replaces vocalization with “subvocalization,” or “silent speech.”
One aim of the speed-reading movement of the 1960s was to eliminate this “subvocalization,” as it’s known.