Early Detection Of Developmental Disorders: The Role Of Canonical Babbling

Theoretical Background: This article addresses early verbal capacities in children with late detected developmental disorders (LDDDs), i.?e., medical conditions that are commonly not diagnosed until toddlerhood. In particular, we focus on autism spectrum disorder (ASD), Rett syndrome (RTT), and fragile X syndrome (FXS), all associated with speech-language and socio-communicative impairments. Partly due to their generally late diagnostic age, little is known about the verbal phenomena during the first years, i.?e., the prediagnostic period, of these disorders. Canonical babbling (CB), for example, is an important preverbal milestone in early speech-language development typically achieved between 6 and 10 months of age. It is suggested that infants who fail to achieve CB within this time window will later present speech-language deficits. Objective: In this article, we review and discuss early verbal atypicalities associated with ASD, RTT, and FXS, with a special focus on CB. We aim to examine whether deviations related to CB may provide valuable cues to facilitate earlier identification of LDDDs. Method: We report on retrospective as well as prospective approaches to study early verbal development in LDDDs. Challenges and methodological issues investigating early verbal capacities in LDDDs are discussed. Results: Studies of CB in infants with ASD, and especially with RTT and FXS, are rare. Heterogeneous findings were revealed. While some studies reported a delayed onset and reduced rate of CB in infants with ASD, RTT, or FXS, others found that a proportion of infants with these disorders do achieve the CB milestone on time and they vocalize comparable ratios of CB to their typically developing peers. However, the existing studies are hard to compare due to differences in study design, measurements, and/or the definition of CB. Recently, researchers began to investigate potential differences in CB of children with LDDDs and typically developing peers at signal level, i.e., the acoustic parameters of CB, exploiting machine-learning technologies. Studies suggest that even if the CB milestone can be regarded as achieved in terms of onset time and ratio, differences may appear with respect to linguistic and acoustic qualities of vocalizations in infants with LDDDs. Discussion and Conclusion: While failing to achieve CB by 10 months of age may prove to be a sensitive sign associated with later speech-language deficits, it is not a specific marker pointing to an LDDD. Nonetheless, deviations in CB flag atypical speech-language development within the first year of life and justify intensive monitoring that may expedite the process of specific diagnosis and set out targeted interventions. This rationalizes the significance of investigating early vocalizations, including CB, aiming at an earlier identification of LDDDs. Further studies that incorporate, e.g., detailed linguistic and signal-level analyses to obtain a reliable picture of the role of preverbal development in general, and CB as age-specific pattern, in the early pathways of such disorders are urgently needed. Given that not all individuals with LDDDs, e.g., ASD, necessarily manifest speech-language deficits, studies of early verbal capacities of individuals with LDDDs ought to take the different outcomes, e.g., later language capacities, into account when interpreting the role of verbal development in the prediagnostic period in early detection of LDDDs.