Northwestern University, Institute for Policy Research:
America’s preoccupation with the “word gap”– the idea that parents in impoverished homes speak less to their children, which, in turn, predicts outcomes like school achievement and income later in life — has skyrocketed in recent years, leading to a rise in educational initiatives aiming to narrow the achievement gap by teaching young children more words.
In a forthcoming article titled “Listen Up! Speech Is for Thinking During Infancy,” to be published in Trends in Cognitive Sciences, Northwestern University psychologist Sandra Waxman and New York University’s Athena Vouloumanos broaden the scope of this issue by assessing the impact of human speech on infant cognition in the first year of life.
“It’s not because [children]have low vocabularies that they fail to achieve later on. That’s far too simple,” said Waxman, the Louis W. Menk Chair in Psychology, a professor of cognitive psychology and a fellow in the University’s Institute for Policy Research. “The vocabulary of a child — raised in poverty or in plenty — is really an index of the larger context in which language participates.”
The brief IPR piece doesn't say that the article will address the impact of speech on emotions, but qualities of speech--volume, rhythm, tonal qualities and tonal shifts--are certainly part of the dance of affective regulation between infant and caregiver. Based on mother-infant observational studies, The Interpersonal World of The Infant by Daniel Stern, offers a great introduction to the subject. While the book isn't primarily about speech, it is discussed briefly, and you can see the broader context of psychological development in which speech plays a significant role.