Directed Vocalizations and Smiles Can Differ As Early As At 6 Month of Age

Background:

Typical infants are innately social, demonstrating direct eye contact as early as in the delivery room. Socially directed vocalizations emerge by age ~12 weeks in the form of reciprocal cooing “conversations,” and consonant babbling by age ~6 months. Although most infant sibling studies report no or minimal abnormalities until after age 9-12 months, clinical experience, along with parental report, strongly suggest differences as early as at age 3-6 months. We previously reported the sensitivity of the Rossetti Infant-Toddler Language Scale to measure differences in social communication at ages 3 and 6 months. We now report additional differences in social interactions presenting by age 6 months. 

Objectives:

To examine whether 6-month-old infants later classified with ASD differed from those later classified as NonSpectrum (NS) in the amount of social interactions when face-to-face with an unfamiliar adult using a Still Face (SF) paradigm.  

Methods:

Twenty-seven infants were enrolled between birth and age 2 months (13 males, 63% Caucasian); they were followed at 2-6months with videotaped social interactions and psychometric instruments, and 9-12⁺months with the Mullen Scales of Early Learning (MSEL) and the ADOS-Toddler Module (ADOS-T). 

At age 6 months, infant-researcher interactions were videotaped with a fiberoptic eyeglass camera while the infant was seated in a car seat, during spontaneous infant-directed “motherese” paradigms, performed pre- (90sec) and post- (90sec) a Still Face (SF) maneuver (30sec).

Once the infants achieved a chronological age of 12 months, a mental age of 12 months measured by the Mullen Scale of Early Learning, and independent ambulation, they were assessed with the ADOS-T for ASD classification.

Videotapes were coded by blind research assistants using Noldus Observer^™ software for the following social interaction behaviors: Direct eye contact; Smiles: directed vs. undirected; and Vocalizations: directed vs. undirected, positive vs. negative. The Observer^™ calculated: a) Proportion of total time, b) Mean duration in seconds, and c) Rate per minute.

Results:

There were no differences between the ASD and NS infants on MSEL scores at 2 or 6 months of age. Eleven of the 27 infants met cutoff criteria for an ASD using the ADOS-T, 4 male and 7 female.

Compared to NS infants at 6 months of age, infants classified with ASD demonstrated:

• a significantly lower rate (p< 0.03)and proportion (p<0.04) of directed vocalizations throughout the entire Paradigm, particularly during the SF (p< 0.02) and Post-SF (p< 0.03) periods;
• a significantly briefer mean duration of directed smiles before the SF (p<0.002); however, the durations during and Post- SF were similar to NS infants.

Conclusions:

These data demonstrate further evidence that deficits in social interaction can be measured as early as at 6 months in at least some infants who are at risk for being diagnosed with an ASD in toddlerhood. This finding lends further support to the ongoing search for easily quantifiable measures which can be used as an early infant screening tool.  Study limitations include a socio-economically advantaged sample, a relatively small sample size, and early classification of ASD with ADOS-T rather than ADOS Module 1 or 2.