Yesterday, Isabella was sitting with her boyfriend at a café, arguing about politics. Neither of them noticed all of the other voices in the room or that some people were staring at them. The allowed Isabella and her boyfriend to focus their attention on their heated discussion, ignoring others around them.

The correct answer is cocktail-party effect

A phenomenon of selective attention in speech perception that allows a listener to attend one of several conversations equally loud that occur simultaneously, factors such as voice quality and directional cues facilitating the task. Conversations recorded on audio tapes in similar circumstances are much more difficult to understand.