Maternal Responsiveness to Babbling

Over the course of my career the most exciting change in speech-language pathology practice has been the realization that we can have an impact on speech and language development by working with the youngest patients, intervening even before the child “starts to talk”. Our effectiveness with these young patients is dependent upon the growing body of research on the developmental processes that underlie speech development during the first year of life. Now that we know that the emergence of babbling is a learned behavior, influenced by auditory and social inputs, this kind of research has mushroomed although our knowledge remains constrained because these studies are hugely expensive, technically difficult and time consuming to conduct. Therefore I was very excited to see a new paper on the topic in JSLHR this month:

Fagan, M. K., & Doveikis, K. N. (2017). Ordinary Interactions Challenge Proposals That Maternal Verbal Responses Shape Infant Vocal Development. Journal of Speech, Language, and Hearing Research, 60(10), 2819-2827. doi:10.1044/2017_JSLHR-S-16-0005

The purpose of this paper was to examine the hypothesis that maternal responses to infant vocalizations are a primary cause of the age related change in the maturity of infant speech during the period 4 through 10 months of age. This time period encompasses three stages of infant vocal development: (1) expansion stage, that is producing vowels and a broad variety of vocalizations that are not speech like but nonetheless exercise vocal parameters such as pitch, resonance and vocal tract closures; (2) canonical babbling stage, that is producing speech like CV syllables, singly or in repetitive strings; and, (3) integrative stage, that is producing a mix of babbling and meaningful words. In the laboratory, contingent verbal responses from adults increase the production rate of mature syllables by infants. Fagan and Doveikis asked whether this shaping mechanism, demonstrated in the laboratory, explains the course of infant speech development in natural interactions in real world settings. They coded 5 and a quarter hours of natural interactions recorded between mothers and infants in the home environment from 35 dyads in a cross-sectional study. Their analysis focuses on maternal behaviors in the 3 second interval following an infant vocalization, defined as a speech-like vowel or syllable type utterance. They were specifically interested to know whether maternal vocalizations in this interval would be responsive (prompt, contingent, relevant to the infant’s vocal behavior, e.g., affirmations, questions, imitations) or nonresponsive (prompt but not meaningfully related to the infant’s vocal behavior, e.g., activity comment, unrelated comment, redirect). This is a summary of their findings:

  • Mothers vocalized 3 times more frequently than infants.
  • One quarter of maternal vocalizations fell within the 3 sec interval after an infant vocalization.
  • About 40% of the prompt maternal vocalizations were responsive and the remainder were nonresponsive, according to their definitions derived from Bornstein et al., 2008).
  • Within the category of responsive maternal vocalizations, the most common were questions and affirmations.
  • A maternal vocalization of some kind occurred promptly after 85% of all infant utterances.
  • Imitations of the infant utterance (also in the responsive category) occurred after approximately 11% of infant utterances (my estimate from their data).
  • Mothers responded preferentially to speech-like vocalizations but not differentially to CV syllables versus vowel-only syllables. In other words, it did not appear that maternal reinforcement or shaping of mature syllables could account for the emergence and increase in this behavior with infant age.

One reason I like this paper so much is that some of the results accord with data that we are collecting in my lab in a project coordinated by my doctoral student Pegah Athari who is showing great skill and patience, having worked her way through through 10 hours of recordings from 5 infants in a longitudinal study (3 months of recording from each infant but covering ages 6 through 14 months overall). The study is designed to explore mimicry specifically as a responsive utterance that may be particularly powerful (mimicry involves full or partial imitation of the preceding utterance). We want to be able to predict when mimicry will occur and to understand its function. In our study we examine the 2 second intervals that precede and follow each infant utterance. Another important difference is that we record the interactions in the lab but there are no experimental procedures, we arrange the setting and materials to support interactions that are as naturalistic as possible. These are some of our findings:

  • Mothers produced 1.6 times as many utterances as their infants.
  • Mothers said something after the vast majority of the infant’s vocalizations just as observed by Fagan and Doveikis.
  • Instances in which one member of the dyad produced an utterance that is similar to the other were rare, but twice as common in the direction of mother mimicking the infant (10%), compared to the baby mimicking the mother (5%).
  • Infant mimicry of the mother is significantly (but not completely) contingent on the mother modeling one of the infant’s preferred sounds in her utterance (mean contingency coefficient = .34).
  • Maternal mimicry is significantly (but not completely) contingent on perceived meaningfulness of the child’s vocalization (mean contingency coefficient = .35). In other words, it seems that the mother is not specifically responding to the phonetic character of her infant’s speech output; rather, she makes a deliberate attempt to teach meaningful communication throughout early development.
  • The number of utterances that the mother perceives to be meaning increase with the infant’s age although this is not a hard and fast rule because regressions occur when the infant is ill and the canonical babbling ratio declines. Mothers will also respond to nonspeechlike utterances in the precanonical stage as being meaningful (animal noises, kissing and so forth).

We want to replicate our findings with another 5 infants before we try to publish our data but I feel confident that our conclusions will be subtly different from Fagan and Doveikis’ despite general agreement with their suggestion that self-motivation factors and access to auditory feedback of their own vocal output plays a primary role in infant vocal development. I think that maternal behavior may yet prove to have an important function however. It is necessary to think about learning mechanisms in which low frequency random inputs are actually helpful. I have talked about this before on this blog in a post about the difference between exploration and exploitation in learning. Exploration is a phase during which trial and error actions help to define the boundaries of the effective action space and permit discovery of actions that are most rewarding. Without exploration one might settle on a small repertoire of actions that are moderately rewarding and never discover others that will be needed as your problems become more complex. Exploitation is the phase during which you use the actions that you have learned to accomplish increasingly complex goals.

The basic idea behind the exploration-exploitation paradox is that long term learning is supported by using an exploration strategy early in the learning process. Specifically, many studies have shown that more variable responding early in learning is associated with easier learning of difficult skills later in the learning process. For early vocal learning, the expansion stage corresponds to this principle nicely: the infant produces a broad variety of vocalizations—squeals, growls, yells, raspberries, vowels, quasiresonants, fully resonant vowels and combinations called marginal babbles. These varied productions lay the foundations for the production of speech like syllables during the coming canonical babbling stage. Learning theorists have demonstrated that environmental inputs can support this kind of free exploration. Specifically, a high reinforcement rate will promote a high response rate but it is important to reinforce variable responses early in the learning process.

In the context of mother-infant interactions, it may be that mothers are reinforcing many different kinds of infant vocalizations in the early stages because they are trying to teach words but the infant is not really capable of producing real words and she has to work with what she hears. She does do something after almost every infant utterance however so she encourages many different practice trials on the part of the infant. It is also possible (although not completely proven) that imitative responses on the part of the mother are particularly reinforcing to the infant. In the short excerpt of a “conversation” between a mum and her 11 month old infant shown here, it can be seen that she responds to every one of the infant’s utterances, encouraging a number of variable responses, specifically mimicking those that are most closely aligned with her intentions.

IDV11E03A EXCERPT

It is likely that when alone in the crib, the infant’s vocalizations will be more repetitive, permitting more specific practice of preferred phonetic forms such as “da” (infants are known to babble more when alone than in dyadic interactions, especially when scientists feed back their vocalizations over loud speakers). The thing is, the infant’s goals are not aligned with the mothers. In my view, the most likely explanation for infant vocal learning is self-supervised learning. The infant is motivated to produce specific utterances and finds achievement of those utterances to be intrinsically motivating. What kind of utterances does the infant want to produce? Computer models of this process have settled on two factors: salience and learning progress. That is, the infant enjoys producing sounds that are interesting and that are not yet mastered. The mother’s goals are completely different (teach real words) but her behaviors in this regard serve the infant’s goals nonetheless by: (1) supporting perceptual learning of targets that correspond to the ambient language; (2) encouraging sound play/practice by responding to the infant’s attempts with a variety of socially positive behaviors; (3) reinforcing variable productions by modeling a variety of forms and accepting a variety of attempts as approximations of meaningful utterances when possible; and (4) increasing the salience of speech-like utterances through mimicry of these rare utterances. The misalignment of the infant’s and the mother’s goals is helpful to the process because if the mother were trying to teach the infant specific phonetic forms (CV syllables for example), the exploration process might be curtailed prematurely and self-motivation mechanisms might be hampered.

What are the clinical implications of these observations? I am not sure yet. I need a lot more data to feel more confident that I can predict maternal behavior in relation to infant behavior. But in the meantime it strikes me that SLPs engage in a number of parent teaching practices that assume that responsiveness by the parent is a “good thing”. However, it is not certain that parents typically respond to their infant’s vocalizations in quite the ways that we expect. In the mean time, procedures to encourage vocal play are a valuable part of your tool box, as described in Chapter 10 of our book:

Rvachew, S., & Brosseau-Lapre, F. (2018). Developmental Phonological Disorders: Foundations of Clinical Practice (Second ed.). San Diego, CA: Plural Publishing, Inc.

 

Advertisements
Leave a comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s

%d bloggers like this: