The Talmud interprets the phrase “speak in your hearts” (Tehillim ) as a reference to Torah study. The Maharsham (Responsa VIII, 19) brings support from this that one fulfills the mitzvah of Torah study through thought, without speaking. The Shulchan Arukh (O.C. 47:3, 4) rules that one does not recite birkhot haTorah for merely thinking, unless one is also writing. The distinction, as expressed by the Levush, is that writing is an action, and thus deserves a b’rakhah.
The Gra argues on the Shulchan Arukh, and assumes that mental study also requires a b’rakhah. The Sha’agat Aryeh (#24) understands the position of the Rambam to be that even if the mitzvah of Talmud Torah is fulfilled mentally, the b’rakhah was only instituted for verbalized learning. The Arukh HaShulchan understands such a position to be reflective of the fact that the primary venue for Torah study is the spoken word, and the written word as well, which ensures that Torah will not be forgotten, and is thus equivalent to speech.
In any event, the Sh’arim Mitzuyanim B’Halakhah, who discusses this topic extensively, disputes the notion of this Talmudic passage as a prooftext. The context of the citation is an internal struggle with one’s negative impulses. Thus, the message is “Speak” words of Torah, to impact upon “your hearts”, where this struggle is taking place.