"What?" "Huh?" "Sorry, I just didn't hear you." Turns out, your friend who never seems to be paying attention to you while they're texting away might actually be temporarily deaf and not completely ignoring you like a total jerk.

For real. A study from University College London found that focusing on a visual task, like choosing the perfect emoji, can render you temporarily deaf to normal-level sounds around you, like someone telling you to put away your phone and pay attention to them.

It's called inattentional deafness and it happens to us all the time. Especially when we try to multi-task, which we actually kind of suck at.

"Modern environments are designed with the assumption that providing information through multiple senses simultaneously will help us process more information more efficiently," Dr. Maria Chait, a professor of neuroscience who worked on the study, told The Huffington Post. "Our work demonstrates that that this assumption is incorrect."

Here's how it works: When you hear a sound, your ear sends information to your brain about it. The brain pulls that information into your awareness. BUT! If your brain is busy doing something visual, it can't properly process that sound input because all of your precious brain resources are occupied. Anything the ear sends to you brain won't be heard.

The study, published in the Journal of Neuroscience, scanned the brains of 13 participants as they completed a demanding visual task. Easier tasks don't suck up brain resources the same way and louder sounds, like a siren or a thunderclap, are strong enough to come through loud and clear, even if the task is as difficult as trying to decipher the subtle nuances of a text that just says "K."