by Emma Ilyaz
Depression is related to a whole host of outcomes, including changes to nonverbal emotional expressions. This can include one’s facial expressions, body language and posture, and their tone of voice (“vocal prosody”—i.e., not what you say, but HOW you say it). Despite some evidence that people with depression have altered vocal prosody, we don’t yet know how vocal prosody differs during emotional speech (e.g., when expressing anger or happiness). This type of speech is thought to be especially important for the parent-child relationship, because parents often use emotional-sounding speech (called “infant-directed speech”) when talking to their young ones. Is emotional vocal prosody different in parents who experienced depression during their child’s lifetime, vs. those who did not? Our study set out to understand whether mothers with or without a recent history of depression had differences in their vocal prosody during emotional expression.
Our study included eighty-one mothers and their 3- to 4-year-old children. Thirty-nine of the mothers had a history of depression during their child’s lifetime, while the rest of them did not. Mothers were recorded while they portrayed twenty different sentences in a neutral, angry, and happy tone of voice. The sentences were made to align with common phrases a mother might say to their child (e.g., “Did you put your shoes away?”). After this, we used a special software to objectively characterize their tone of voice! This involved editing each of the recordings to ensure they had good sound quality, then putting them into a software to extract the values of their pitch (the up and down pattern of speech), their intensity (their loudness), and their speech rate (how fast or slow they’re speaking). Additionally, we asked four hundred and ten other adults to listen to these recordings and tell us how intense, recognizable, and authentic mothers’ emotional speech was. We looked to see whether there were differences between mothers with and without a history of depression on our objective speech analysis and whether these differences were able to be picked up by listeners.
In our objective speech analysis, we found that when expressing happiness, mothers with a history of depression had less range in their pitch (i.e., sounded more monotone), and spoke slower than mothers without a history of depression. While we did not find that people with depression were rated any differently by the independent listeners, we did find that recordings with less pitch range and slower speech rate were rated to be less intensely, recognizably, and authentically happy. This signals to us that while there are objective differences in speech between mothers with and without a history of depression, the way that people are perceiving these differences could depend on each individual mother’s speech pattern.
These findings suggest that mothers with depression may be speaking in a way that blurs the emotional intent of their message. In turn, this might be affecting the way that their children learn about emotion. There is still much to learn about how different vocal prosody impacts children. But, since vocal prosody can easily be modified, an early suggestion might be to encourage mothers who have a history of depression to exaggerate their happy voice when speaking to their young children to help clarify their emotional messages!