The Relationship Between Rhythmic Movement and Babble Onset in Infants at Heightened Risk for ASD

Background:      In typically-developing infants, the onset of reduplicated babble (i.e., vocalizations with repeated consonant-vowel sequences; [bababa]) is accompanied by a significant increase in rhythmic motor activity in the upper limbs (e.g., shaking, banging; Iverson et al, 2007), suggesting coupling of the vocal and motor systems. However, research examining these behaviors in the infant siblings of children with autism spectrum disorder (ASD; High Risk; HR) finds that this relationship is attenuated relative to infants without an older sibling with ASD (Low Risk; LR; Iverson & Wozniak, 2007). It is possible that instability of the vocal and motor systems in the subset of HR infants who go on to have ASD accounts for differences between LR and HR infants; however, this hypothesis has yet to be tested.

Objectives:     The present study was designed to examine change in rhythmic movement at babble onset in LR infants and in three groups of HR infants: No Diagnosis, Language Delay, and ASD.

Methods:    Participants included 52 HR infants who were videotaped at home monthly from 5-14 months. A comparison group of 30 LR infants was observed bi-weekly from 2-19 months. Sessions for both samples consisted of 45 minutes of naturalistic and semi-structured play. The present study focused on the visits one month prior to and at the onset of reduplicated babbling. Babble onset was identified using parent report and experimenter observation. All instances of rhythmic movements (i.e., movements repeated in the same form at least 3 times within intervals of 1sec; Thelen, 1979) were coded, and rates of rhythmic movement per 10 minutes were calculated.

At 36 months, HR infants received a diagnostic evaluation using the ADOS-G (Lord et al., 2000) and clinical judgment.  Eight HR infants received an ASD diagnosis (HR-ASD). Seventeen HR children with language delays were identified (HR-LD); and the remaining 27 HR infants did not meet ASD or LD criteria (No Diagnosis; HR-ND).

Results:     Wilcoxon signed rank tests were used to assess whether rates of rhythmic movement changed significantly from pre-babble to babble onset. Rates of rhythmic movement increased significantly in both the LR (Mdn_pre = 3.73, Mdn_babble = 6.86) and HR-ND ( Mdn_pre = 3.38, Mdn_babble = 7.89) groups (p’s <.05). A similar increase was also apparent among HR-LD infants ( Mdn_pre = 5.08, Mdn_babble = 9.23), but the change was only marginally significant (p=.068). In contrast, rates of rhythmic movement decreased in the HR-ASD group ( Mdn_pre = 12.39, Mdn_babble = 10.70), although the change was not significant (Z=-.840, p>.05). Inspection of individual data revealed that 6 of the 8 ASD infants decreased in rate of rhythmic movement from pre-babble to babble onset.

Conclusions:      For infants with no diagnosis—regardless of risk status—rhythmic movement significantly increased at babble onset, suggesting a coupling of the vocal and motor systems. Only infants with an eventual ASD diagnosis displayed a different pattern in rhythmic movement, lending support to the hypothesis that disorganization and instability in the vocal and motor systems may be a component of development in ASD.