Imagine you're getting a BMI that can send data into your brain, but doesn't measure any signals from your brain. So you can feed arbitrary data into your brain, but you don't have any ability to control stuff through the BMI. What would the most useful data-stream to plug into the brain be?

pic related, it's a wristband with several vibrating nubs that can be hooked up to arbitrary data sources to pass information to your brain through your skin. The primary use of the device is to assist deaf people. The wristband has a mic on it and can translate the audio into vibrations on the skin to give deaf people some of the awareness that you can only get through sound, but there's an API that lets you stream any data you want to it through a bluetooth network.