Taken from this list of research summaries. Skepticism warning: taken from a website that sells sign language courses for babies, and those papers were written by the people running the website (I had originally found the research summaries on another website, TinyFingers.com, but it appears they just copied the text off of BabySigns.com without any attribution - not even in their links section). So, how much is marketing and how much is sound research?This is the article in which we present the most important findings from our NIH-sponsored longitudinal study of the impact on verbal development of purposefully encouraging infants to use symbolic gestures. Standardized tests of both receptive and expressive language development had been administered at 11, 15, 19, 24, 30, and 36 months to both an experimental group of babies (Baby Signers) and two control groups. Results demonstrated a clear advantage for the Baby Signers, thereby laying to rest the most frequently voiced concern of parents – that Baby Signing might hamper learning to talk. In fact, the good news is that Baby Signing actually facilitates verbal language development.
I looked a bit for some more objective review of the research, I found this (summary only, the paper's behind a paywall):
Should parents be encouraged to teach their hearing infants to communicate using gestural signs? Does signing in infancy advance child behaviour and development as claimed by many commercially available products for parents? To answer these questions, a review was undertaken to evaluate currently available research studies that examined the effectiveness of prelingual signing for normally developing, hearing infants. Databases, reference lists and the Internet were searched for relevant documents using a pre-determined search protocol. Seventeen reports met the review’s inclusion criteria and were retrieved and evaluated. The review failed to support claims that signing facilitates language development, due to insufficiencies in scientific methods and to equivocal results.I also found this paper, which says:
Claims that signing with infants benefits language development are examined. Fourteen infants aged 19 to 23 months were tested on their comprehension and production of novel labels in a word learning task. Infants participated in two conditions. In the Sign + Word condition, infants learned both a signed and vocal label for a novel toy, whereas in the Word Only condition, infants were taught only a vocal label for the novel toy. Results showed that when children participated first in the Sign + Word condition, their comprehension and production abilities were lower than when trained first in the Word Only condition. Previous exposure to sign language was not related to infants’ performance on the word learning task, although there was a marginal effect of previous language ability on performance. Contrary to previous findings (e.g., Goodwyn, Acredolo, & Brown, 2000), the sign and word combination did not facilitate children’s learning of spoken labels. Possible explanations for these findings are discussed.It includes a review of the literature (many of which is papers by Goodwyn and Acredo), and in conclusion:
This study does not directly debunk any of the fundamental claims from the baby signing programs, i.e. that teaching baby signs to infants between 6 and 9 months of age will aid in communication. It simply debunks some of the extrapolations many of these programs use in order to recruit more customers.I'd have to read up a bit more on this, but I'm less warm to the idea of sign language for babie than I was when I started off.