Publications

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Long, H. L., Eichorn, N., & Oller, D. K. (under review). A probe study on vocal development in two infants at risk for cerebral palsy.

A probe study on vocal development in two infants at risk for cerebral palsy.

The present work examined the utility of tracking canonical babbling ratios longitudinally as a measure of onset and consolidation of canonical babbling in two infants at risk for cerebral palsy. We collected all-day home audio recordings from both infants between 5-16 months of age. Canonical babbling ratios were calculated from five-minute segments and follow-up diagnostic data were collected around 24 months. Ten typically developing infants were included for comparison at four age points. Both the at-risk infants and the typically developing infants demonstrated greater variability than expected in their canonical babbling ratios over time. The infants at risk demonstrated somewhat delayed trajectories of CBRs compared to the TD infants. The two were later diagnosed with different levels of cerebral palsy and speech impairment severity. Studying canonical babbling and other prelinguistic milestones in this population may inform our perspective of the involvement of the motor system in the vocal domain.


Long, H. L., Ramsay, G., Bowman, D. D., Burkhardt-Reed, M. M., & Oller, D. K. (under review). Social and endogenous motivations in the emergence of canonical babbling in infants at low and high risk for autism.

Social and endogenous motivations in the emergence of canonical babbling in infants at low and high risk for autism

There is a growing body of research emphasizing the role of intrinsic motivation and endogenous activity to support the development of cognitive systems alongside the well-established role of social interaction. The present study longitudinally evaluated canonical babbling across the second-half year of life, when canonical babbling becomes well-established. We compared segments rated as having high and low levels of turn taking and independent vocal play in 98 children at low and high risk for autism spectrum disorder. Segments were extracted from all-day home audio recordings to observe infants in naturalistic settings. Canonical babbling ratios (CBR) were determined based on human coding along with Likert-scale ratings on the level of turn taking and vocal play in each segment. We observed highly significant differences in CBRs between risk groups during high and low vocal play, but high and low levels of turn taking yielded a weaker effect. There were also interactions of CBR with age, risk, and vocal function variables. We conclude that social and endogenous/exploratory motivations may drive both high- and low-risk infant tendencies to produce their most speech-like vocalizations.


Koopmans, C., Sakash, A., Soriano, J., Long, H. L., & Hustad, K. C. (in press). Functional communication abilities in students with cerebral palsy: Association with impairment profiles and school-based therapy goals. Language, Speech, and Hearing Services in the Schools. doi.org/10.31219/osf.io/c2q4m

Functional communication abilities in students with cerebral palsy: Association with impairment profiles and school-based therapy goals

Aim. To examine the relationship between functional communication skills, underlying speech, language, and cognitive impairments, and school-based speech pathology services in students with cerebral palsy (CP).

Method. Thirty-five participants with CP who had active Individualized Education Programs (IEPs) were classified according to the Communication Function Classification System (CFCS). Participants completed laboratory assessments of speech, receptive language, executive functioning, and non-verbal cognition. Each participant’s speech and language IEP goals were coded into treatment units, then categorized into seven, mutually exclusive target goal areas. Non-parametric analyses were employed to examine differences among CFCS groups in the number of deficit areas and the number of goal areas from the IEP. Descriptive analyses were used to evaluate the extent to which deficit areas and goal areas in the IEP co-occurred by CFCS level.

Results. Those in more involved CFCS levels demonstrated more severe speech, receptive language, and cognitive impairments. However, there were no significant differences in the number of deficit areas across CFCS group. Regardless of CFCS level, there were no differences in the number of treatment goals specified in the IEP. Literacy was the only goal area addressed across all CFCS levels. Those in the most involved CFCS levels had AAC goals, but those with more moderate restrictions on functional communication who also had markedly reduced speech intelligibility did not typically have speech or AAC goals.

Interpretation. Individuals with CP across CFCS levels demonstrate variability in their underlying deficit profiles, suggesting that measures of both functional communication and of underlying deficits are necessary to provide a complete picture of communication needs. Literacy goals were common across all CFCS levels, but AAC goals were limited to the most severely involved individuals, suggesting that continuing education may be necessary to support SLPs in developing treatments involving the integration of AAC and speech to foster functional communication at school.


Gipson, T. T., Ramsay, G., Ellison, E. E., Bene, E. R., Long, H. L., & Oller, D. K. (2021). Early vocal development in tuberous sclerosis complex. Pediatric Neurology, 125, 48-52. doi.org/10.1016/j.pediatrneurol.2021.08.009

Early vocal development in tuberous sclerosis complex

Objective: To determine whether entry into the canonical stage, canonical babbling ratios (CBR) and the level of volubility (vocal measures) are delayed in infants with Tuberous Sclerosis Complex (TSC), we completed human coding of their vocalizations at 12 months and compared the results to typically developing infants with no clinical features (TD/NCF). Methods: We randomly selected videos from 40 infants with TSC from the TACERN database. All 78 videos were coded in real-time in AACT (Action Analysis, Coding and Training). Results: Entry into the canonical stage was delayed in the great majority of the infants with TSC. The CBR for the TD/NCF infants was significantly higher than for the infants with TSC (TD/NCF mean = .346, SE = .19; TSC mean = .117, SE = .023). Volubility level in infants with TSC was less than half that of TD/NCF infants (TD/NCF mean = 9.82, SE = 5.78; TSC mean = 3.99, SE = 2.16). CBR and volubility were also lower in TSC infants than in TD/NCF infants recorded all-day at home. Conclusions: Entry into the canonical stage was delayed, while canonical babbling ratios and volubility were low in infants with TSC. Assessing prediction of neurodevelopmental outcome using these vocal measures in combination with non-vocal measures will be the focus of planned studies in this high-risk population.

Burkhardt-Reed, M. M., Long, H. L., Bowman, D. D., Bene, E. R., & Oller, D. K. (2021). The origin of language and relative roles of voice and gesture in early communication development. Infant Behavior and Development, 65, 101648. doi.org/10.1016/j.infbeh.2021.101648

The origin of language and the relative roles of voice and gesture in early communication development

Both vocalization and gesture are universal modes of communication and fundamental features of language development. The gestural origins theory proposes that language evolved out of early gestural use. However, evidence reported here suggests vocalization is much more prominent in early human communication than gesture is. To our knowledge no prior research has investigated the rates of emergence of both gesture and vocalization across the first year in human infants. We evaluated the rates of gestures and speech-like vocalizations (protophones) in 10 infants at 4, 7, and 11 months of age using parent-infant laboratory recordings. We found that infant protophones outnumbered gestures substantially at all three ages, ranging from >35 times more protophones than gestures at 3 months, to >2.5 times more protophones than gestures at 11 months. The results suggest vocalization, not gesture, is the predominant mode of communication in human infants in the first year.

Oller, D. K., Ramsay, G., Bene, E., Long, H. L., & Griebel, U. (2021). Protophones, the precursors to speech, dominate the human infant vocal landscape. Philosophical Transactions of the Royal Society B: Biological Sciences, 376(1836), 20200255. doi.org/10.1098/rstb.2020.0255

Protophones, the precursors to speech, dominate the human infant vocal landscape

Human infant vocalization is viewed as a critical foundation for vocal learning and language. All apes share distress sounds (shrieks and cries) and laughter. Another vocal type, speech-like sounds, common in human infants, is rare but not absent in other apes. These three vocal types form a basis for especially informative cross-species comparisons. To make such comparisons possible we need empirical research documenting frequency of occurrence of all three.

The present work provides a comprehensive portrayal of these three vocal types in the human infant from longitudinal research in various circumstances of recording. Recently the predominant vocalizations of the human infant have been shown to be speech-like sounds, or “protophones”, including both canonical and non-canonical babbling. The research shows that protophones outnumber cries by a factor of at least five based on data from random-sampling of all-day recordings across the first year. The present work expands on the prior reports, showing the protophones vastly outnumber both cry and laughter in both all-day and laboratory recordings in various circumstances. The data provide new evidence of the predominance of protophones in the infant vocal landscape and illuminate their role in human vocal learning and the origin of language.

Long, H. L., Bowman, D. D., Yoo, H., Burkhardt-Reed, M. M., Bene, E. R., & Oller, D. K. (2020). Social and endogenous infant vocalizations. PLoS ONE, 15(8), e0224956. doi.org/10.1371/journal.pone.0224956

Social and endogenous infant vocalizations

Research on infant vocal development has provided notable insights into vocal interaction with caregivers, elucidating growth in foundations for language through parental elicitation and reaction to vocalizations. A role for infant vocalizations produced endogenously, potentially providing raw material for interaction and a basis for growth in the vocal capacity itself, has received less attention. We report that in laboratory recordings of infants and their parents, the bulk of infant speech-like vocalizations, or “protophones”, were directed toward no one and instead appeared to be generated endogenously, mostly in exploration of vocal abilities. The tendency to predominantly produce protophones without directing them to others occurred both during periods when parents were instructed to interact with their infants and during periods when parents were occupied with an interviewer, with the infants in the room. The results emphasize the infant as an agent in vocal learning, even when not interacting socially and suggest an enhanced perspective on foundations for vocal language.


Oller, D. K., Griebel, U., Bowman, D. D., Bene, E. R., Long, H. L., Yoo, H., & Ramsay, G. (2020). Infant boys are more vocal than infant girls. Current Biology, 30, R417-429. doi.org/10.1016/j.cub.2020.03.049

Infant boys are more vocal than infant girls

Although it is generally assumed females have a language advantage over males, Oller et al., studying all-day recordings of 100 infants, found that boys in the first year of life produced more speech-like vocalizations than girls and that the effect size was more than four times larger than the commonly reported female language advantage.


Oller, D. K., Caskey, M., Yoo, H., Bene, E. R., Jhang, Y., Lee, C.-C., Bowman, D. D., Long, H. L., Buder, E. H., & Vohr, B. (2019). Preterm and full term infant vocalization and the origin of language. Scientific Reports, 9, 14734. doi.org/10.1038/s41598-019-51352-0

Preterm and full term infant vocalization and the origin of language

How did vocal language originate? Before trying to determine how referential vocabulary or syntax may have arisen, it is critical to explain how ancient hominins began to produce vocalization flexibly, without binding to emotions or functions. A crucial factor in the vocal communicative split of hominins from the ape background may thus have been copious, functionally flexible vocalization, starting in infancy and continuing throughout life, long before there were more advanced linguistic features such as referential vocabulary. 2-3 month-old modern human infants produce "protophones", including at least three types of functionally flexible non-cry precursors to speech rarely reported in other ape infants. But how early in life do protophones actually appear? We report that the most common protophone types emerge abundantly as early as vocalization can be observed in infancy, in preterm infants still in neonatal intensive care. Contrary to the expectation that cries are the predominant vocalizations of infancy, our all-day recordings showed that protophones occurred far more frequently than cries in both preterm and full-term infants. Protophones were not limited to interactive circumstances, but also occurred at high rates when infants were alone, indicating an endogenous inclination to vocalize exploratorily, perhaps the most fundamental capacity underlying vocal language.


Long, H. L., Oller, D. K., & Bowman, D. D. (2019). Reliability of listener judgments of infant vocal imitation. Frontiers in Psychology, 10, 1340. doi.org/10.3389/fpsyg.2019.01340

Reliability of listener judgments of infant vocal imitation

There are many theories surrounding infant imitation; however, there is no research to our knowledge evaluating the reliability of listener perception of vocal imitation in prelinguistic infants. This paper evaluates intra- and inter-rater judgments on the degree of "imitativeness" in utterances of infants below 12 months of age. 18 listeners were presented audio segments selected from naturalistic recordings to represent in each case a parent vocal model followed by an infant utterance ranging from low to high degrees of imitativeness. The naturalistic data suggested vocal imitation occurred rarely across the first year, but strong intra- and inter-rater correlations were found for judgments of imitativeness. Our results suggest salience of the infant's vocal imitation despite its rare occurrence as well as active perception by listeners of the imitative signal. We discuss infant vocal imitation as a potential signal of well-being as perceived by caregivers.