Flash Exposure Compensation

I typically adjust the flash exposure compensation down a stop or two when using fill flash outdoors, so I'm familiar with the effect it has on exposure, but how does the camera adjust exposure when this value is set?

In my limited understanding, the following parameters will affect exposure:

• Shutter speed
• Aperture value
• Metering method
• ISO speed

It seems these values are not modified in a flash exposure compensation mode.
So exactly what does the camera do in this situation?
Is it just adjusting the final brightness value or is something more complex going on?

The flash fires a pre-flash to determine what output it needs to produce a properly exposed image. When you dial in negative exposure compensation, the flash output is reduced according to the exposure calculation.

Ah, that makes sense.
Thanks Sean!