Colwyn Trevarthen studied babies and their mothers, observing the communication and subtle movements between them. He has links to music therapy with other theorists.^{[further explanation needed][11]}

There are numerous purposes and benefits of infant directed speech, including positive effects on the early development of infants and children, and aid in the ability of infants to bond with their caregivers. In addition, infants begin the process of speech and language acquisition and development through infant directed speech.^[12] Infant directed speech may also contribute to the modulation of infant attention, assist infants in determining relevant syntactic qualities including phonetic boundaries, and convey positive emotion to infants^{[citation needed]}. The more expressive infant directed speech is, the more likely infants are to respond to this method of communication by adults.^[13]

Perhaps the most important benefit of infant directed speech is what it provides to the development of language for infants and children. It has been found that the children who learn the fastest are those who receive the most acknowledgement and encouragement of what they say, who are given time and attention to speak and share, and who are questioned.^[14]For instance, it has been found that six-month-olds can discriminate between medial position syllables in words with multiple syllables when infant directed speech is used^{[citation needed]}. Therefore, infant directed speech is a powerful tool in providing a base for language acquisition. Infants are able to apply principles of this practice to larger words and sentences as they learn to process language.^[15]

Infant directed speech also aids infants in selecting appropriate social partners. Although infants have a range of social cues available to them regarding who will provide adequate care, infant directed speech serves as an additional indicator as to which caregivers will provide developmental support. When adults engage in infant directed speech with infants they are ultimately providing them with positive emotion and attention, signaling to infants that they are valued.^[16]

Infant directed speech can also serve as a priming tool for infants to notice the faces of their caregivers. Due to the nature of infant directed speech, infants are more sensitive to the pitch and emphasized qualities of this method^{[citation needed]}. Therefore, when caregivers utilize infant directed speech they are expanding the possibility for their infants to notice and process their facial expressions. This effect could in part be due to the fact that infants associate infant directed speech with positive facial expressions such as smiling. Infants may be more likely to respond to infant directed speech if they expect to receive a positive response from their caregiver. Regardless, infant directed speech serves as a tool to aid infants in responding to facial expressions from caregivers, which in turn stimulates both language and social development.^[17]

Research suggests that infant directed speech promotes the processing of word forms and allows infants to remember words when asked to recall them in the future. As words are repeated through infant directed speech, infants begin to create mental representations of each word. As a result, infants who experience infant directed speech are able to recall words more effectively than infants who do not.^[18]

Research has shown that infants can pick up on the vocal cues of infant directed speech and will often pattern their babbling after it.^[19]

The implications of the lack of the use of infant directed speech are equally as important to recognize. Research suggests that children of depressed mothers who do not regularly use infant directed speech display delayed language development^{[citation needed]}. Even when depressed mothers provide their infants with positive faces, infants do not respond to their attempts at infant directed speech, and in turn do not benefit from this important method of language acquisition. Infants are unable to create the link between speech and visual face movements in situations such as these. When fathers who are not depressed are able to provide the stimulation of infant directed speech for their children, infants respond well and are able to compensate from the deficit left by their mothers^{[citation needed]}. Unfortunately, it is likely that if infants do not receive adequate infant directed speech from their mothers they will generalize this response to all females^{[citation needed]}. This too can inhibit language and speech development. Therefore, this deficit can be especially harmful to infants with depressed mothers and little contact with male caregivers.^[20] Socioeconomic status has been found to influence the development of vocabulary and language skills. Lower-status groups tend to be behind the development of children in higher-status families. This finding is thought to be due to the amount of time parents spend with the child and the ways they interact; mothers from higher-status groups are found to say more to their children, use more variety, and speak in longer sentences.^[21] Families with a lower-status might just have less time to spend focusing on interactions.

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