Caregivers Shift Their Response Behavior to Infants’ Vocal Sequences Over Development

• In Event: The Diversity of Caregiver-child Coordination and its Contributions to Language Development

Abstract

An important achievement in early vocal development is the emergence of multi-syllablic sequences of babbling. Few studies, however, have proposed developmental mechanisms for this phenomenon. Vocal learning studies on humans (Elmlinger, Schwade, & Goldstein, 2019), songbirds (Carouso-Peck & Goldstein, 2020), and primates (Gultekin & Hage, 2018) show that adults who coordinate their vocalizations with those of their offspring create contingent social feedback that facilitates learning of more advanced vocal patterns. While previous work has focused on the timing of feedback to individual syllables, here we investigate caregivers’ responses to babbling sequences to assess their sensitivity to sequential structure in infants’ vocalizations.

In a longitudinal design, 30 caregiver-infant dyads participated when infants were 5 (M = infant age = 5.32 mo) and 10 months of age (M = infant age = 9.73 mo; 17 females, 13 males). Dyads engaged in 15-minute free-play sessions. Caregivers were asked to play as they normally would at home. Audio-visual recordings of infants’ vocalizations and caregivers’ speech during free-play were obtained. Infants’ vocalizations were segmented into vocal sequences if they were bounded by silent gaps longer than 1 second in duration. Vocal sequences contained at least two syllables. For each infant vocalization, we determined whether it elicited a caregiver response. Caregiver responses were defined as any verbal behavior which occurred within 2 seconds after infants’ vocalizations.

We found that caregivers were more likely to respond to infants’ sequential vocalizations compared to individual syllables at 5 and 10 months (5 mo: t(24)=-2.52,p =.011; 10 mo: t(29)=-5.02,p=.0001) (Figure 1). To control for possible effects of vocalization duration on response elicitation, we compared the mean duration of sequences which did and did not elicit a caregiver response. The mean duration of 5-month-old’s sequences that elicited a response was almost significantly longer (M=3.22 s, SD=1.67 s) than those that did not elicit a response (M=2.33 s, SD=1.08 s,p=.050). However, 10-month-old’s sequences which elicited a response (M=2.12 s, SD=1.07 s) did not differ from the duration of sequences which did not elicit a response (M=1.82 s, SD=.88 s,p=.104). To the extent that caregivers shifted their response behavior to infants’ sequential vocalizations, caregivers may exhibit a higher ratio of responses to infants’ vocal sequences as compared to all vocalizations. We compared caregivers’ sequence response ratios to a chance-level sequence response ratio that was computed via pseudo-sampling, as in Suanda et al. (2017) (Figure 2).

We found that caregivers’ sequence response ratios were above chance levels to 10-month-old infants (M=.35, SD=.18, t(29)=2.05,p=.024), but at chance levels to 5-month-old infants (M=.19, SD=.17, t(29)=.90,p=.187) (Figure 2). Similar to effects found at the level of individual syllables (Goldstein & Schwade, 2008), the increase in responses that vocal sequences elicit from caregivers may drive infants to structure their vocalizations as sequences, a vocal precursor to spoken language.

Over infants’ development, caregivers selectively respond to infants’ vocalizations which incorporate sequential structure. By selectively responding to infants’ vocalizations that incorporate more mature speech characteristics, caregivers provide infants with additional sources of information which guide infants’ communicative development.

Authors

• Steven L Elmlinger, Cornell University
  Presenting Author

• Jennifer Schwade, Cornell University
  Non-Presenting Author

• Michael H. Goldstein, Cornell University
  Non-Presenting Author