Keyboard response rate is too low, and character suggestion popups appear periodically I'm typing on my Retina MacBook Pro, and the response rate on the keyboard is terrible. It's like typing on an LCII that is trying to run Mac OS X. As I type, the computer seems to be thinking ridiculously hard about what it is doing. Periodically, these silly character suggestions will appear next to the cursor:



The response rate is so bad that I am literally typing this message one painstaking character at a time, and waiting for it to appear on the screen before typing the next. I estimate &lt; 20 WPM. Keys are randomly repeating as well. 

Any idea what this is or why it is happening? This is the second time  I've had this issue. I haven't been able to find any info in the Apple forums about it, I'm guessing because I don't know what this phenomenon is called.
The characters appear when a key is held down, it's the same as on an iPhone to make it easier to type accents and things. Those are alternative S characters.

You can turn it off using:

defaults write -g ApplePressAndHoldEnabled -bool true


in Terminal.

However, that doesn't explain the overall response rate, just the characters.

For the keyboard rate check Accessibility in System Prefs. You might have Slow Keys enabled in the Keyboard section. You might also want to check under options at the Acceptable Delay in that panel.