What is the effect of motherese on development?

Question

Most cultures (Falk, 2009) have a special type of language that is used to talk to children: infant-directed-speech (IDL; or informally, motherese, baby talk). For instance, Fernald (1992) argues that motherese is an evolved phenomena that was selected for. This suggests that it has a benefit to child development, hence my questions:

1. What benefit does IDL provide children?
2. How do the features of IDL benefit the cognitive development of children?
3. Are there benefits beyound effects on language-acquisition?

Notes

• The only benefit I am familiar with (shameless self plug) is in helping avoid reversal-errors in pronoun acquisition but Kaznatcheev (2010) is only a theoretical prediction based on a particular computational model of questionable (1, 2) empirical validity.

• I am interested in the developmental benefit of the very specific language used in IDL, not about the benefit of maternal care in general.

References

Fernald, A. (1992). "Human maternal vocalizations to infants as biologically relevant signals: An evolutionary perspective." In J. H. Barkow, L. Cosmides, & J. Tooby (Eds.) The adapted mind: Evolutionary psychology and the generation of culture (pp. 391-428).

Falk, D. (2009). Finding our tongues: Mothers, infants and the origins of language. New York: Basic Books.

Kaznatcheev, A. (2010). "A Connectionist Study on the Interplay of Nouns and Pronouns in Personal Pronoun Acquisition." Cognitive Computation 2(4): 280-284.

Answer 1

Motherese may play a role in emotional development.

Soken and Pick write:

Concurrent with the exaggerated speech of motherese, there are probably exaggerated facial displays, allowing infants to explore the particular aspects of the face... Child-centered displays may serve as opportunities for learning about affective events.

Walker-Andrews (1997) also suggests that

the presence of the face acts as a setting for attending to the affective quality of the voice.

Yet, according to a recent, extensive review on motherese (Saint-Georges et al., 2013), its role in emotion and cognition is still an open area of research.

References

• N. H. Soken and A. D. Pick, “Intermodal Perception of Happy and Angry Expressive Behaviors by Seven‐Month‐Old Infants,” Child development, vol. 63, no. 4, pp. 787–795, 1992.

• A. S. Walker-Andrews, “Infants' perception of expressive behaviors: differentiation of multimodal information.,” Psychological Bulletin, vol. 121, no. 3, p. 437, 1997.

• C. Saint-Georges, M. Chetouani, R. Cassel, F. Apicella, A. Mahdhaoui, F. Muratori, M. C. Laznik, and D. Cohen, “Motherese in Interaction: At the Cross-Road of Emotion and Cognition? (A Systematic Review),” PLoS ONE, vol. 8, no. 10, p. e78103, Oct. 2013.

Answer 2

I believe motherese exists to teach the infant to discriminate phonemes in the native language. Kuhl et al. (2005) show that during the first year language critical period, infants gain an increased ability to discriminate between phonemes of the native language, while their ability to discriminate between phonemes of non-native languages declines. Additionally, their ability to discriminate phonemes is initially language-neutral. Kuhl (2003) further shows a strong correlation between mother speech clarity and infant phonetic discrimination ability.

So if clarity is so important, why talk to children in semi-gibberish and not normal speech? One possibility is that motherese emphasizes certain sounds to enhance the perceptual discrimination. Karzon (1983) investigates this idea, with positive results. To us motherese sounds odd, but in reality it is providing a clearer phonetic structure for the infant to learn.

It's likely that the mother's desire to talk to her baby in motherese, and the babies appreciation of it are traits that co-evolved. Perhaps, like Falk suggests, motherese is an exapted remnant of some early hominid proto-language.

This type of interaction might also have a role in the larger structure of mother/child bonding. But I feel it's unlikely that it evolved for that particular reason. What's more likely is that it was simply co-opted into that mechanism.

References

Karzon, R.G. (1985) Discrimination of polysyllabic sequences by one- to four-month-old infants Journal of Experimental Child Psychology 39(2): 326-342.

Kuhl, P.K., Conboy, B.T., Padden, D., Nelson, T., & Pruitt, J. (2005) Early Speech Perception and Later Language Development: Implications for the "Critical Period" Language Learning and Development 1(3-4): 237-264.

Liu, H-M., Kuhl, P.K., Tsao, F-M. (2003) An association between mothers’ speech clarity and infants’ speech discrimination skills Developmental Science 6(3): F1-F10.

Answer 3

Fonagy and Target, although they do not specifically cite the term 'Motherese', believe that what they call 'Marking'- signalling an unreality or playfulness in mirrored displays of affect can play a crucial role in the development of a faculty they call 'Mentalization'.

According to their model, newborns experience affect as all-pervading, and do not see it as limited to a self. By internalising mirrored affect displays by the primary caregiver they are able to conceptualise their own affect on a second order (symbolic) level, are able to 'play' with their own feelings as the mother brings affect into the realm of the pretend. Thus they implicate improper marking in later development of borderline personality disorders.

Here's a paper of theirs on the subject, although I recommend their book, which is considerably more expansive.

Edit: Sorry, off the internets for a month. Here are some useful quotes:

Take the case of pretend play: here markedness is conveyed by a series of salient perceptual features that distinguish a pretend action or pretend emotion expression from a real one. Knowing looks, slightly tilted head, high pitch and slowed down down, exaggerated intonation and contour, schematic, abbreviated or only partial execution of action schemes... ...all mark for the child that the pretend expression is categorically different from its realistic equivalent- that it is "not for real". We have argued... ...that in the case of adaptive parental affect-mirroring interactions, the affect-reflective emotion display is also modified by the same kinds of transformations... (Fonagy, Gergley, Jurist and Target, "Affect regulation, Mentalization and Development of the Self" p296 , Other Press 2002- linked above)

Frustratingly, this was the most explicit exposition of marking behaviours I could find in the book, which is mainly theoretical. You will immediately observe that what is described is not all motherese, nor only motherese- but you will agree, I hope, that there is a not-inconsiderable overlap between the two- and that the wedding of IDL to such concepts is not, so to speak, of shotgun ilk. To say that the function of motherese was precisely the above would certainly be wrong- but I would hope you would concurr that as an adaptation it would confer advantage in part for this reason, were Fonagy et al's hypothesis

...[T]hat the perception of markedness activates the yound child's metarepresentational system (Leslie 1987) which allows for "decoupling" of the expression from its referents in actual reality. (Ibid, p296)

true.