Vocalizations in Autism Spectrum Disorders Between 18 and 24 Months

Background: Since there is currently no biological marker for ASD, there is a need for research into possible early behavioral markers. Few studies have investigated vocal patterns in children with Autism Spectrum Disorders (ASD) under 24 months of age.

Objectives: The purpose of this prospective, longitudinal study of the FIRST WORDS Project was to describe differences in vocalizations within and outside of communicative acts produced by 18-24 month old children with ASD, developmental delay (DD), and typical development (TD). In addition, for children with ASD, concurrent and predictive relationships between vocalizations and developmental level were investigated.

Methods: Videotapes of Communication and Symbolic Behavior Scales (CSBS) Behavior Samples for 125 children between 18 and 24 months of age (50 ASD, 50 TD, and 25 DD) were analyzed to obtain precise measures of vocalizations. Transcribable vocalizations (TVs) were coded to describe phonetic complexity and number of syllables. Nontranscribable vocalizations (NTVs) were coded according to specific categories of typical and atypical sounds.  Social, speech, and symbolic composites were obtained from the CSBS (mean = 21.1 months) and Verbal Developmental Quotients (VDQ) were obtained from the Mullen Scales of Early Learning (MSEL; mean = 36.8 months).

Results: Children with ASD used a significantly lower proportion of vocalizations with consonants than children with TD. In addition, children with ASD used a significantly higher proportion of atypical NTVs than children with TD and a significantly higher proportion of distress NTVs than both children with TD and DD. For the ASD group, the frequency of vocalizations and the frequency of TVs correlated significantly with developmental levels both concurrently and at 3 years of age. In addition, communicative vocalizations late in the second year were found to uniquely predict expressive language outcome at age 3 over and above noncommunicative vocalizations.

Conclusions: By 18 to 24 months of age many vocalization measures significantly differentiated children with ASD from children with TD, with a higher proportion of distress vocalizations differentiating children with ASD from both children with TD and DD.  The importance of communicative vocalizations for later language development is highlighted by the results of this investigation.