To make any progress on this question at all, we need first to come up with some definition of internal monologue. Even if we may need to modify it later, there has to be a starting point.
Otherwise, nothing can be established at all, because for any statement there always will be someone's understanding of "internal monologue" for which the statement is true, and someone's else understanding for which the statement is false...
Otherwise, nothing can be established at all, because for any statement there always will be someone's understanding of "internal monologue" for which the statement is true, and someone's else understanding for which the statement is false...