Potential early identification markers for children with autism spectrum disorder: Unusual vocalizations and theoretical explanations

Abstract

<p id=C10>Early identification and intervention of children with autism spectrum disorder (ASD) are critical to their developmental outcomes. Vocalizations are sounds produced by children before they learn to talk. These can be divided into two categories: nonspeech-like and speech-like. Speech-like vocalizations include consonant and vowel sounds. Nonspeech-like vocalizations are natural, vegetative sounds that do not resemble speech. The common analysis indicators of nonspeech-like vocalizations in children with ASD are fundamental frequency, pause length, and duration of crying. Commonly used analytical indicators for speech-like vocalizations are vocal complexity and vocal communication. <p id=C11>Compared with typically developing children, those with ASD display a higher fundamental frequency of crying, yet shorter pauses in its length and duration. Atypical crying may represent an early biomarker for children with ASD that aids in early detection. The complexity of speech-like vocalizations in children with ASD is unusual and manifests as a lower or higher vocal complexity than those with typical development. Unusual vocal complexity appears to be a potentially useful indicator of emergent ASD, especially high vocal complexity, which may be an early identification marker for regression in children with ASD. When compared to typically developing children, children with ASD display low rates of vocal communication production, which may also be a useful early identification marker for the presence of ASD. <p id=C12>The theoretical explanations for unusual vocalizations mainly include: motivation orientation theories, neuromotor orientation theories, perceptual orientation theory, and social feedback orientation theory. In motivation orientation theories, potential sources of variation in vocal complexity are strong intrinsic motivation of special interests and social motivation deficits. The social motivation deficits may also lead to less communicative vocalizations in children with ASD. According to neuromotor orientation theories, the immaturity or disorder of nerves leads to atypical vocal complexity in children with ASD. The delay in the development of sitting posture limits the acquisition of speech-like vocalizations in children with ASD. Damage to the vagal cranial nerve complex leads to higher fundamental frequency, shorter pauses between cry episodes of crying, and shorter crying episodes in children with ASD. The perceptual orientation theory suggests that atypical auditory processing of speech sound stimuli in children with ASD makes them unable to learn speech-like vocalizations, affecting the development of vocal complexity. Social feedback orientation theory proposes that the effectiveness of the social feedback loop of children with ASD is reduced. Thus, if the number of iterations of the social feedback loop decreases, their speech-like vocalizations are further reduced. <p id=C13>Future research may consider in (1) exploring the possibility of unusual vocalizations as unique early identification markers for children with ASD, (2) strengthening the study of crying in early screening of children with ASD, (3) constructing an automatic learning classification model based on the strongest predictive acoustic parameters, (4) analyzing the influence of intrinsic and social motivation on speech-like vocalizations in children with ASD, and (5) investigating the neural mechanisms of unusual speech-like vocalizations. These evidence may be helpful for early identification and intervention of children with ASD.