Plus, some parents of deaf babies adopt a "speech first" approach, saying that they are OK with their children signing later. Also, some professionals discourage signing by newly identified deaf babies to make sure they learn to talk.
Does sign hurt speech?
Available ResearchDr. Linda Acredolo and Dr. Susan Goodwyn are the authors of the book Baby Signs: How to Talk with Your Baby Before Your Baby Can Talk. Acredolo, Goodwyn, and Catherine Brown teamed up on a research paper, "Impact of symbolic gesturing on early language development," that was published in 2000 in the Journal of Nonverbal Behavior.
The study involved 103 11-month-old hearing babies. The babies were divided between a group learning sign language, and a group that did not learn sign language. By the time the signing babies were two years old, they were talking more than the average two year old. At three years old, the signing babies were talking more than the average three year old. By age eight, the signing babies scored higher on IQ tests than the non signing babies.
The full study is lengthy and technical. The key sentence in the study is:
Thus, at every level of analysis, the data are consistent in demonstrating an advantage in verbal language development for those children who were encouraged to include symbolic gestures in their early communicative repertoires.Sources:
Summary: https://www.babysigns.com/index.cfm/fuseaction/institute.research/research.cfm (Accessed September 26, 2007).
Full study: https://www.babysigns.com/index.cfm/fuseaction/institute.language_development_study/language_development_study.cfm (Accessed September 26, 2007). Originally published in Journal of Nonverbal Behavior, 24 (2), pp. 81-103.