There have been experiments, I believe, where they have found that newborns will recognize their mother’s voice out of a selection of that and other women’s. So they probably hear something in there. Maybe it’s just insufficient research.
http://www.scientificamerican.com/article/fact-or-fiction-babies-ex/
Fact or Fiction?: Babies Exposed to Classical Music End Up Smarter
Is the so-called “Mozart effect” a scientifically supported, developmental leg up or a media-fueled “scientific legend”?
“I would simply say that there is no compelling evidence that children who listen to classical music are going to have any improvement in cognitive abilities,” adds Rauscher, now an associate professor of psychology at the University of Wisconsin–Oshkosh. “It’s really a myth, in my humble opinion.”
I know my daughter got really quiet, really quick when I started talking to her quietly right after she was C-Sectioned out of my wife. Not scientific, I know, but I am certain to this day as I was at the time that she recognized my voice while not recognizing the voices of the nurses or others in the room.