Preverbal Vocalizations in Infant Siblings of Children with ASD

Background:

Prelinguistic vocal behavior is known to be related to speech development in typical children (Oller, 1999; McCune & Vihman, 2001). However, prelinguistic behavior has been shown to be atypical in preschoolers with ASD (Sheinkopf et al., 2000), and expressive language delay is a nearly universal feature of the development of children with ASD (Tager-Flusberg et al., 2005).

Objectives:

The present study examined prelinguistic vocal behavior in infants at high risk for developing ASD as a result of having older sibling diagnosed with ASD, and compared these to vocalizations of infants at low risk for ASD, who did not have a diagnosed sibling. Our aim was to determine whether infants at risk for ASD show delays or differences from typical development in terms of their production of speech sounds, syllable structures, and prosody in the prelinguistic period. Such differences, if identified, could be useful in early identification of high risk children who are in the greatest danger of developing ASD or related disorders.  

Methods:

Subjects were drawn from those participating in a longitudinal study of behavior and development of infant siblings of children with a diagnosis of ASD. As part of participation in the longitudinal study, infants are seen at at least four time points during the first year of life. At each visit standard assessments of behavior and development, as well as data from experimental tasks were collected. The present report presents cross-sectional analysis of vocal productions collected at the 6, 9, and 12 month visits. Vocal samples were audiorecorded during a five-minute free-play mother-child interaction, in which mothers were presented with quiet toys, asked to play with their baby and to attempt to encourage the baby to vocalize. Cross-sectional vocalization data from twenty children in each of the two diagnostic groups were analyzed at each of the three visits. Analyses included:

Consonant inventory (Shriberg & Kwiatkowki, 1994)

Syllable structure level (Olswang et al., 1987)

% Canonical syllable production (Oller, 1998)

Atypical prosodic productions (Sheinkopf et al., 2000).

Analyses were completed by two trained raters with experience in phonetic transcription who were blind to participants’ age and risk status. Point-to-point reliability for ratings was over 80%.

Results:

There were no between-group differences in vocal behavior at six months. At nine months, high risk infants, as a group, produced fewer canonical syllables, fewer consonant types, less mature syllable structures, and more atypical prosody than those in the low risk group. By twelve months, only differences in prosody persisted. The high risk group appeared to have “caught up” in terms of sound and syllable production with their low-risk peers.

Conclusions:

These findings suggest that infants at high risk for ASD do show differences from low risk peers in vocal production at certain points in the first year of life. These differences may be helpful, in conjunction with other measures,  in clarifying risk status. In addition, the suggestion of delay in prespeech development seen in these data may contribute to understanding the trajectory of expressive language acquisition in ASD.