Babies are born ready to learn any language in the world, and they have linguistic super-powers that many adults don't.
For instance at 6 months old, they can distinguish between sounds in different languages that non-bilinguals hear as the same, such as an English "d" and a Hindi "d." They can also tell if someone is English or French without sound based on the mouth shapes of the speaker and rhythms. Only bilinguals retain these abilities throughout life.
Really cool, right? But around 10 months old, babies typically stop being able to make these distinctions. As they get better at perceiving a native language, they are less sensitive to non-native sights and sounds, says Janet Werker, psychologist at the University of British Columbia in Vancouver.
Researchers are interested in probing this "critical period" of language development. They want to know what factors affect the window of time after which a baby loses sensitivity to a non-native language.
Werker's new study in the journal Proceedings of the National Academy of Sciences explores babies' language development in relation to depression and a class of antidepressants called serotonin reuptake inhibitors. This is not a study designed to help researchers recommend for or against antidepressant medications, she says, but rather to explore language development milestones.
Given that as many as 20% of women have a mood disorder during pregnancy, and up to 13% of them take an antidepressant while carrying a child, assessing the impact of the condition and the treatment is important.
There were three groups of participants: 32 babies whose mothers who took antidepressants during pregnancy, 21 babies whose mothers had depression during pregnancy but did not take medication for it, and 32 babies whose mothers did not have depression.
The babies had to perform discrimination tasks involving sounds ("d" in English vs. Hindi) and visual speech (watching people speak different languages without sound).
Researchers found that depression and antidepressants did seem to make a difference in terms of when the babies showed sensitivity to different languages.
The babies in the control group, whose mothers did not have depression, performed as expected: They tended to succeed in language discrimination tasks at 6 months old and failed at 10 months old.
But the infants whose mothers had depression (but were not taking antidepressants) failed at 6 months and succeeded at 10 months. That means their critical period for language sensitivity was delayed.
Interestingly, the infants whose mothers were taking antidepressants failed both times. It appears that they were more "advanced" than both groups, in the sense that the language sensitivity window had already passed.
What's going on here? Researchers aren't sure, and they don't know if it's good or bad. One explanation for delay in the depressed-but-not-medicated group is that those kids weren't being exposed to as much engaging speech because their mothers were depressed.
Alternatively, the brain chemicals from the mother associated with depression could have something to do with it. And the antidepressants could be impacting the child's brain development in the group whose mothers took these medications.
Are there long-lasting consequences of delays, or advancements, in this critical period of language sensitivity? No one knows. More research needs to be done in order to determine the implications of the findings of this study.