WASHINGTON Recordings that claim to stimulate baby brain development may actually slow vocabulary development in infants if they are overused, U.S. researchers reported on Wednesday.
For every hour per day spent watching baby DVDs and videos, infants aged 8 to 16 months understood an average of six to eight fewer words than babies who did not watch them, Frederick Zimmerman of the University of Washington and colleagues found.
Older toddlers were not harmed or helped by the videos, the researchers reported in the Journal of Pediatrics.
"The most important fact to come from this study is there is no clear evidence of a benefit coming from baby DVDs and videos, and there is some suggestion of harm," Zimmerman said in a statement.
"The bottom line is the more a child watches baby DVDs and videos, the bigger the effect. The amount of viewing does matter."
Zimmerman and colleagues conducted random telephone interviews with more than 1,000 families in Minnesota and Washington with babies and asked detailed questions about television and video viewing.
Parents of the 8- to 16-month-olds were asked how many words like "choo-choo," "mommy" and "nose" their child understood. Parents of the toddlers were asked how many words like "truck," "cookie" and "balloon" their children knew.
"The results surprised us, but they make sense. There are only a fixed number of hours that young babies are awake and alert," said Andrew Meltzoff, a psychologist who worked on the study.
"If the 'alert time' is spent in front of DVDs and TV, instead of with people speaking in 'parentese'-- that melodic speech we use with little ones -- the babies are not getting the same linguistic experience," Meltzoff added.
"Parents and caretakers are the baby's first and best teachers. They instinctively adjust their speech, eye gaze and social signals to support language acquisition. Watching attention-getting DVDs and TV may not be an even swap for warm social human interaction at this age. Old kids may be different, but the youngest babies seem to learn language best from people."
Dr. Dimitri Christakis, a pediatrician at Seattle Children's Hospital Research Institute who worked on the study, said parents frequently asked him about the value of such videos.
"The evidence is mounting that they are of no value and may in fact be harmful," Christakis said.