They're not transcribing it, so much as selecting the keys one would need to press in order to type the text. That is, the correct key lights up, and they move the cursor and mentally "click" to select it. This serves two purposes:
- WPM is a difficult metric to "game", since if they make a mistake they have to select the backspace key, and then select the correct key again.
- It's a proof of concept demonstration that a human (e.g. in the BrainGate[1] clinical trial) could use this prosthetic system to communicate in text. When a human were driving the system, the keys wouldn't light up; they'd just type freely.