Development of vocal repertoires in non- and minimally verbal autism spectrum disorder

Abstract

The autism spectrum comprises a substantial 30% of individuals said to be non- or minimally verbal. While these produce no phrase-speech by definition, they often do vocalize. However, their exact vocal repertoires remain unknown. The present study aimed to advance on this front by developing a new annotation scheme for nine such individuals, adapting categories used to profile pre-verbal neurotypical children. In a second step, vocalization variables were related to microstructural metrics (fractional anisotropy, FA, and myelin water fraction, MWF) of a crucial white-matter speech-related tract, the arcuate fasciculus (AF). Results revealed that at

a group level, participants produced significantly more syllabic, or speechlike, than non- syllabic vocalizations. The proportion of words marginally exceeded that of word

approximations. Furthermore, the vowel and consonant repertoire resembled that of neurotypical infants. There were no significant correlations between vocalization and either FA or MWF in the AF. These new findings refute the expectation that vocalizations in individuals with NMVA are predominantly non-speech-like and substantiate the need to look for the neural basis of NMVA also in non-speech-related language territory in the brain.