Motherese, or infant-directed speech, is a form of speech used by mothers and caregivers with their infants. It is characterised by several distinct acoustic features (Binder et al 2009:1946) such as exaggerated prosody (Bryant & Barrett, 2007:746), longer vowels and higher pitch (Liu et al, 2009:909) and the use of shorter, grammatically simpler utterances (Williamson 2014). There have been numerous studies investigating the usage of infant directed speech (henceforth IDS) in situations of child/caregiver interactions, and the development of the child's linguistic abilities (Farran et al (2016), Liu et al (2009)). This paper will investigate the significance of IDS for the linguistic development of infants. This will be done by discussing several of the aforementioned studies as well as examining data from the CHILDES database, specifically targeting infants' reactions to IDS. Finally, this paper will conclude that motherese is indeed significant and beneficial for the child's linguistic development.
IDS is hypothesised to have developed in early hominin species due to the physiological changes seen in their evolution (Falk 2004:491). These included the enlargement of the birth canal, which allowed for increased brain size and mental capacity of the species. This resulted in the lack of development at birth compared to other animals, due to the length of time required for their full development, which increased dependence of infants on their mothers (Falk 2004:492). According to Ross (2001:765), infant riding of their mothers during foraging behaviour and other tasks diminished in humans, whereas it remains in some other primates to the present day. It is hypothesised (Falk 2004:492) that the early hominin mothers placed their dependent infants down while performing tasks, thus amplifying the need for comforting distal gestural and vocalised communication between mothers and their infants in place of physical contact.
The use of musical speech and exaggerated gestures acts as a scaffold upon which the infant develops linguistic competence later in life (Falk 2004:491). According to an investigation by Cooper et al (1997:477), infants prefer IDS of strangers over their adult directed speech, and show no preference over the type of speech of their mothers. This could indicate that IDS contributes to making the infant feel comfortable and open to communication with caregivers, enhancing their interest in speech (Binder et al 2009:1946), even if it is not necessarily the only speech style that facilitates the learning of their first language.
Evidence for this can be seen in several videos of child/caregiver interaction on the CHILDES database. For example the Demuth 2002 data, filmed in Lyon, France, shows 1 year old Anaïs's mother talking with her and an investigator in French. Initially the child is tentative yet inquisitive, and her mother attempts to capture her interest and help her relax into the recorded interaction, using IDS. The child is engaged with the adults, indicated by her facial expressions and eye contact. This behaviour demonstrates her curiosity and involvement in the interaction, and it is clear that she is encouraged by the use of IDS by the caregivers. The investigator asks Anaïs (line 24),
"Qui c'est?" ("Who is it?")
using IDS, raising her pitch before providing the answer herself (line 26)
"C'est Ana." (It's Ana.)
"C'est toi bébé." ("It's you baby") Anaïs' mother adds (line 28). These IDS interactions by the caregivers with the infant are to encourage her to engage with them, and also to help her become relaxed with them as they know she is apprehensive:
"petite timide" ("little shy") (line 33).
The utterances used by the adults are characteristic of IDS, using a soft gentle tone, higher pitch and simple phrases.
The mother asks (line 46)
"Tu avances?" ("are you coming (forwards)?")
and repeats her question in a hushed whispering tone.
Line 48 shows Anaïs responding with a short vocalisation. This is an example of IDS being used by caregivers to encourage an infant to engage in interaction with them, and to contribute her own prelinguistic vocalisations. While it cannot be claimed from this evidence that IDS exclusively supports the linguistic development of children, it is clear that its use by the caregivers in this situation allows the infant to feel more at ease in the interaction, and also encourages her attempts at communicating vocally by making it clear to her that her participation is desired and welcomed. The behaviour seen in this instance reinforces the suggestion by Bryant & Barrett (2007:746) that in the earlier stages of development, IDS functions as an attention and interaction instigating device rather than a source of specific linguistic instruction.
This leads on to the concept of recognising intentions in IDS, and whether it is easier to do so than with adult directed speech (ADS). If so, this would indicate that IDS is indeed a useful tool in supporting a developing child’s comprehension of linguistic meanings. Bryant & Barrett (2007) highlight the importance of prosody in the communication of intention, which is used in both ADS and IDS, but is exaggerated in the latter. In their innovative research, Bryant & Barrett (2007) collate recordings of American English speakers using both ADS and IDS to convey four 'intention categories' consisting of prohibition, approval, comfort and attention. They then use informants from an indigenous South American people known as Shuar, and observe whether they understand the intentions of a language they do not speak merely from the prosody. This is performed for both ADS and IDS, and aims to ascertain whether IDS is present and recognisable universally in all languages and cultures as a specialised infant/caregiver interaction mechanism.
The findings of the Bryant & Barrett (2007) study indicate that the Shuar subjects were able to not only distinguish ADS from IDS, but also distinguish intentions significantly more easily in IDS than ADS. While the informants did find the contrast between approval and comfort and between prohibition and attention somewhat ambiguous at times, the results still clearly show the significance of the exaggerated prosody and intonation of IDS for the communication of intentions, specifically the contrast between the positive and negative. The fact that these results were seen in informants of an indigenous and non-literate community who had no knowledge of the language in question also provides strong evidence for the universality of IDS as a human tool of infant/caregiver interaction.
In order to understand whether IDS is significant in the linguistic development of children it is also necessary to examine the cultural differences in the use of IDS, as all cultures raise linguistically competent offspring, but may possess different practices when interacting with their infants. It has been suggested that in some more traditional societies IDS does not exist at all (Broesch & Bryant (2015:32-33)). This is perhaps as infants are not seen as suitable speech partners while they are still to develop linguistically, such as the case of behaviour observed in Western Samoa (Ochs (1982), in Broesch & Bryant (2015:33)).
Broesch & Bryant (2015) examined the acoustic differences in the IDS of mothers from three different cultures: rural Fijians, Kenyan Bukusu (both grouped into non-Western) and middle class Americans (Western). The mothers in all cultures were recorded interacting with their infant positioned at arms length. They were instructed to interact vocally with their child as normal and that they should not hold their infant, but physical contact was permitted. The researcher spoke with the mothers at the beginning and end of the recording, to sample their adult directed speech. The observations were that the mothers from all cultures increased their vocal pitch when addressing their infants, and varied it when using adult directed speech. The mothers also slowed their speech rate in IDS compared to ADS, which was also consistent cross-culturally. Broesch & Bryant's 2015 research was the first of its kind to analyse the acoustic properties of IDS in such traditional cultures and compare the results with the IDS of Western mothers. Their results strongly support the hypothesis that IDS is a universal phenomenon and its prosodic features are similar cross-culturally. This would indicate that motherese is indeed significant for the process of child language acquisition, since language is a universal competence of humans. However, in order to fully understand the extent of its significance further investigation into the consequences of situations where IDS is perhaps lacking or neglected will be necessary. This may present difficulty due to ethical reasons, and opportunities for study may only present themselves in rare cases such as those of socially neglected children.
It can be concluded that motherese is certainly not irrelevant in the linguistic development of infants. It is a phenomenon that is seen across cultures, both industrialised and traditional, and is hypothesised to have evolved alongside human evolution (Falk 2004:492). The intentions of motherese can be understood by observers who do not speak or understand the language in which it is produced (Bryant & Barrett, 2007). While IDS is not necessarily vital for the acquisition of adult-level linguistic competence, the matters discussed in this paper show that motherese does not appear to be detrimental to child language acquisition. The benefits of IDS can be seen in the mother/child interaction from the Demuth (2002) data as discussed. IDS is clearly an effective attention attaining device (Bryant & Barrett, 2007:746), which also allows the caregiver to communicate intentions to the infant (Bryant & Barrett, 2007). The use of IDS also enhances the interest of infants in speech (Binder et al 2009:1946), and encourages them to make their own vocal contributions, especially during early development (observed in the Demuth 2002 data). The raised pitch, a characteristic of IDS, perhaps indicates to the infant that they are the one being addressed, and comforts them due to the distinction that they can make between the speech of a caregiver, one who provides security, and a non-interlocutor. This is indicated in the fact that infants have been observed to prefer the IDS of strangers over their non-IDS (Cooper et al, 1997:477). Motherese clearly makes a beneficial contribution to the linguistic development of an infant, it is a system that can be clearly identified by the infant from its acoustic and prosodic characteristics, and encourages them to engage and understand the meaning of the language that is being used, without the prerequisite of full linguistic proficiency. However, it cannot yet be claimed that IDS is so vital for child language acquisition that without it a child would be rendered alingual. It is preferred to consider motherese a framework upon which an infant attains linguistic competence, used in conjunction with other experiences over the course of the infant's development.