No, Abigal is not an alien baby and she wasn't abducted so that someone could study her. She is hooked up for her hearing test. I am always amazed by how our technology has brought us to where we are today.
Abby must be fully asleep in order for the hearing test to be performed and when ever the computer detects that she has awaken, the test is paused. Noise is sent through the ear muffs and her brain lengths are measured to determine whether she hears that sound or not.
She passed with flying colors, of course I could have told you that. Whenever Heidi speaks that little girl picks her head up to listen to her mom. She can hear just fine.