The gemara develops a 3 way machlokes as to whether one is required to hear what they are saying for mitzvos that are dependent on amira such as kriash shema and brachos. We pasken like R. Yehuda that lichatchila one must hear what they are saying but they can be yotzei bidieved even if they don't hear what they are saying. In the discussion the gemara compares this to one who says ברכת המזון בלבו, which would seem to imply that a person can be yotzei even without articulating the words with their mouth. However, Rashi 15a implies that when the braisa speaks about saying birchas hamazon in one's heart, it doesn't literally mean in one's heart, it means that they don't hear the words that they are saying. Rabbeinu Yona writes this explicitly, we pasken הרהור לאו כדבור דמי, so the entire discussion here is when there is actual dibur, just not audible. The gemara at the very end asks, how can one be yotei brachos that aren't audible, the pasuk says הסכת ושמע ישראל, which implies that hearing what you are saying is essential. The gemara responds that the pasuk of הסכת ושמע ישראל is not speaking about other mitzvos and brachos, rather about talmud torah. Rashi explains that this does not mean that when one learns there is a requirement to hear what one is reading. Rather, the gemara 63b darshens from this הסכת that one should form groups and not study alone. Rashi is clearly bothered by interpreting the gemara to say that one must read out loud when learning, because the mitzvah of limud ha'torah is a mitzvah in the mind, not in the mouth. A similar idea is expressed by the Gr"a cited in the biur halacha in hilchos birchas hatorah. The Shulchan Aruch seems to make the halacha of whether הרהור in Torah requires a birchas hatorah to be dependent on הרהור כדבור דמי, to which the Gr"a responds that even if הרהור is not like speech, it would still require a birchas hatorah because the mitzvah of talmud torah is והגית בו יומם ולילה. Meaning the mitzvah of Talmud Torah is not a speech related mitzvah, it is a mitzvah for one to be mentally involved in Torah study.
However, the Shulchan Aruch HaGraz in Hilchos Talmud Torah (2:12) writes:
וכל אדם צריך ליזהר להוציא בשפתיו ולהשמיע לאזניו כל מה שלומד בין במקרא משנה ותלמוד, אלא אם כן בשעת עיון להבין דבר מתוך דבר. וכל מה שלומד בהרהור לבד ואפשר לו להוציא בשפתיו ואינו מוציא, אינו יוצא בלימוד זה ידי חובת מצות ולמדתם אותו וכו' וכמו בכל המצות התלויות בדבור שאינו יוצא בהן ידי חובתו בהרהור אא"כ שומע מפי המדבר שהשומע כעונה בפיו.
The Ba'al Hatanya seems to learn our gemara כפשוטו, that the mitzvah of Talmud Torah is essentially a mitzvah of dibur and can only be fulfilled if it is read in an audible way. According to this approach, Talmud Torah is actually stricter than other brachos and krias shema where one can be yotzei bidieved even if they don't hear what they are saying. The gemara considers the pasuk of הסכת ושמע ישראל to be me'akeiv, so that one is not yotzei talmud torah even bidieved unless they actually hear what they are saying.