system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When I'm in a crowded room and want to focus on one conversation happening across the room, why does that conversation seem to become more audible, or more easily discerned?

Mostly just curious about how your body knows to essentially block out, or make most other sounds fade out as you focus on that one particular sound, conversation, etc.
gpt
It's called selective focus or sometimes it's called the cocktail party effect. There is a difference between perception (actually putting brain power to interpret stimuli) and simple detection by your senses. So when you focus on this one conversation, your brain only interprets signals here and effectively ignores the rest of the sounds in the room.