They're crazy! Kids start learning language much earlier than that.
When my daughter was born we had deaf foster kids and used Total Communication. That's signing and talking at the same time and was encouraged by the school our foster kids attended.
Our daughter began making up her own signs at about five months,. When she wanted her diaper changed she'd hold her feet up in the air and when she wanted to nurse she'd pull my shirt up. A week or so later she began lifting her own shirt or skirt to signify that she wanted to nurse. She used her first legitimate sign at about seven months, and started using spoken words soon after that. By the time she was a year old she had a vocabulary of 30 words and signs, but refused to use a word for something she knew the sign for and vice versa.
You may think she was unusually advanced, but babies born into deaf families often start using legitimate signs at about four months. Our daughter's learning was probably delayed because she was learning two languages at the same time.
Many people are using sign language with their babies now, but if they don't use it all the time to communicate with each other as well as with the baby it won't have the same effect. (And if you want to teach your baby Sign language please use real ASL, not made up "Baby Signs." You wouldn't use a bunch of nonsense syllables and call them "Baby Chinese" or "Baby Spanish.")
If you want to read about the study you can see it at http://www.sciencedaily.com/releases/2006/03/060322141610.htm but don't believe everything you read just because scientists say it's true.