The cocktail party effect is the ability to listen selectively despite a noisy environment. The term comes from the observation that even in a crowded cocktail party room, a person can carry on a conversation with one person by “tuning in” to them and “tuning out” everything else.

If you think about it, it’s amazing that we can direct our focus to parse a desired noise source—say, a television—over the voice of the person sitting next to you. Of course, it ...