I heard it helps if you select a few people who seem to pay the most attention—better sitting at far end of audience to make sure you don't lower your voice too

I heard it helps if you select a few people who seem to pay the most attention—better sitting at far end of audience to make sure you don't lower your voice too much—and ‘talk’ to those few listeners, cycling between them. I encountered this once and I suspect it was because I was thinking about presentation, not focused on delivering my point to the audience, not caring about it enough. Possibly also the audience that time didn't really care about my point. (Hard to find origin, as factors seem to worsen one another: you care less → audience cares less → … → your thoughts wander, you lose context.)