A systematic review suggests marked differences in the prevalence of infant‐directed vocalization across groups of populations

Abstract

Anthropological reports have long suggested that speaking to young children is very infrequent in certain populations (notably farming ones), which is in line with scattered quantitative studies. A systematic review was undertaken to use available literature in order to estimate the extent of population variation. Database searches, expert lists, and citation searches led to the discovery of 29 reports on the frequency of vocalizations directed to infants aged 24 months or younger, based on systematic observations of spontaneous activity in the infant's natural environment lasting at least 30 min in length. Together, these studies provide evidence on 1314 infants growing up in a range of communities (urban, foraging, farming). For populations located outside of North America, the frequency with which vocalization was directed to urban infants was much higher than that for rural infants (including both foraging and farming, medians = 12.6 vs. 3.6% of observations contained infant‐directed vocalization behaviors). We benchmarked this effect against socio‐economic status (SES) variation in the United States, which was much smaller. Infants in high SES American homes were spoken to only slightly more frequently than those in low SES homes (medians = 16.4 vs. 15.1% of observations contained infant‐directed vocalization behaviors). Although published research represents a biased sample of the world's populations, these results invite further cross‐population research to understand the causes and effects of such considerable population group differences.

Characterization of children's verbal input in a forager-farmer population using long-form audio recordings and diverse input definitions

“…What counts towards children's input is defined in a wholly different way in another study using the LENA©automated algorithm [14], which only considers near and clear speech from adults, discarding faint speech, speech that overlaps with other sounds, and even speech from other children. Gilkerson and colleagues studied 329 North American English learners (aged 2-48 months), and their data suggests children hear an average of 3.5 min/h of speech in total, 3 including both child-directed and overheard speech. 4 Somewhere in between these two definitions of what counts as input, Wesleder and Fernald also used near and clear speech from adults from the automated LENA©algorithm, but complemented this with exhaustive listening of every 5-minute section in every recording from 29 Spanish-learning 19-month-old infants growing up in the USA, to decide whether speech in each 5-minute block was mostly child-directed or overheard [15].…”

“…suggesting that speech from other adults should be considered as part of children's effective 2 Note that in the Yélî sample, a significant increase with age was found for speech from other children, so the percentage of TCD coming from adults is higher for younger than older children in that sample. 3 They estimated that children encountered an average of 1,025 adult words per hour, which amounts to about 3.5 minutes per hour (henceforth min/h) of total input [assuming each word is about 200 milliseconds long; see supplementary material in 4]. 4 The authors report that speech quantity is higher for the younger infants in the sample (under 4 months).…”

“…Some work suggests that there is high variation in the prevalence of child-directed speech. For example, a recent systematic review estimated that children growing up in urban settings (in post-industrialized, larger, and richer societies, where formal schooling is compulsory) hear ~8 min/h of vocalization directed to them (henceforth, TCD vocalizations), whereas children in rural settings (which also happened to be from small-scale, subsistence farming or hunter-gatherer societies in the summarized literature) hear one third of that [3]. The review focused on estimates emerging from systematic behavioral observations: The observer follows the infant or child around (for, e.g., 2 hours), and notes whether anyone vocalized towards the child during an observation period (e.g., every 15 seconds).…”

Mothers Reveal More of Their Vocal Identity When Talking to Infants

“…Even though Swiss listeners showed a high sensitivity in differentiating IDS from ADS in the Swiss speakers (mean A' across 31 listeners = 0.79; see STAR methods), Swiss ADS had notable IDS influences. In addition, differences between ADS and IDS registers are continuous rather than categorical, and specific acoustic attributes and prevalence differ according to cultural background, geographic region, and individual identity [43][44][45] .…”

Combining observational and experimental approaches to the development of language and communication in rural samples: Opportunities and challenges

“…This paper brings together six researchers with expertise in the use of both observational and experimental child language research methods in rural settings. Young children from rural settings are under-represented in developmental research (e.g., Cristia, 2022), particularly in research taking an experimental approach. We here provide an overview of salient work that (a) combines observational and experimental perspectives on the same linguistic or communicative phenomenon and (b) is based in a rural community.…”