Based on past work I've done with external EEG caps (not implants), I would imagine this prices requires training before brainwaves can be interpreted as words. E.g. the subject thinks the word "hello" as brain activity is recorded, and later the computer tries to fuzzy match current brain activity with previous records to identify the correct word (or image).

If that process applies with this implant, you'd have to very intentionally focus on a pre-trained word before it would show up on the screen.