Internal microphone does not register input in System Preferences -> Sound but registers in dictation and speech

My machine is MacBook Pro (Retina, 13-inch, Late 2013), OS 10.10.1 (14B25).

I just tried to make a voice call in Google Hangouts, and Hangouts does not pick up any sound.

I checked System Preferences -> Sound -> Internal Microphone, and the Input Level meter shows no activity - not when I talk, clap, or hit the case.

How do I fix this and get my internal microphone to register an input correctly?

More info:

System Preferences -> Dictation and Speech -> Dictation has an icon that says "Internal Microphone" and appears to register sound. In fact, it seems to be very sensitive.

Some things I have checked:

• Under Sound -> Internal Microphone, Input volume is turned all of the way up.


• I have no devices plugged into the headphone jack.


• In Audio MIDI Setup, I've checked that Built-in Microphone isn't muted.


• I shut down the computer and started it up again, and again while holding command-option-p-r (although I don't actually know what that does). It didn't help.