the listener valued only as an ear — "Bruce Green inserts low affirmatives and…"
Bruce Green inserts low affirmatives and ‘No shit’s and ‘Fucking-A’s, etc., at just the right places to communicate his attentions to Lenz. Which Lenz admires.
Context
For Lenz, talking is not communication but cognition — he thinks by talking at someone — so the other person is needed not as an interlocutor but as an ear, a source of well-timed "No shit"s that keep the monologue running. What Lenz admires in Green is exactly his fitness as an instrument: attentive, non-rat, and content to supply affirmations rather than replies. The relationship is real to Lenz and one-directional by design; the listener's whole value is that he receives.