Actually, we not only hear and participate, but we are there to assist at Mass. 
I really do not want to get into the scrum that is going on here in this thread, but "assist", in this context, is a curious turn of phrase to the everyday English-speaker. It seems that here, it is in the sense of the French
assister à, which does not mean "help with" or "participate in", but rather, "attend". There is a similar construction in Spanish. It is a figure of speech peculiar to the traditional Mass, and for that reason, I use it assertively when referring to the Mass and my presence at it. My son hears me use it liberally when, in homeschool religion class, I say that "we assist at the Holy Sacrifice of the Mass". It's a shamelessly pre-Vatican II turn of phrase, and as such, is to be cherished and maintained.
We do not "assist" the priest --- he and the acolyte have got that entirely under control --- rather, we unite
spiritually with the Holy Sacrifice, which is no way is dependent upon us for its proper celebration. If you want to follow along in the missal and recite the acolyte's responses
sotto voce, that's your prerogative --- Pope St Pius X urged us to "pray the Mass" (no quarrel with that, far from it) --- but such recitation is entirely optional and adds nothing to the Mass.