We hypothesized that infants and toddlers later diagnosed with a pervasive developmental disorder (PDD-NOS and autism), would have anomalies in their social interactions. Those children later diagnosed with PDD-NOS (by DSM IIIR criteria) have distinctive social behavior that is on a continuum between typically developing children and those eventually diagnosed with autism.

25 videotapes of children diagnosed with PDD were selectively copied to show social events (e.g., birthday parties, holidays) prior to diagnosis when the child was between the ages of 12 to 30 months. These tapes were assessed for social and object engagement. These data were compared with those of 25 typically developing children matched for age. Independent blinded observers, recorded percentage of time the subjects showed object and social engagement. The same videotapes were assessed for specific anomalies in social behavior(avoids being held) and communication (pointing, gazing). This aspect of the study used a coding system developed by Osterling and Dawson (1994). Independent blinded observers, coded the tape for 25 specific behaviors on 10 or more 1 minute samples from the tapes.

There was significant difference between the social engagement of the typical children and those later diagnosed with PDD (stat. value p=0.0001). There was no difference in the mean frequencies of object engagement across groups. Those items that showed significant differences included, “looks at faces” (p=0.012) and “follows verbal directions”(p=0.001). Those children later diagnosed with PDD-NOS had mean frequencies of some social interactions and communicative skills (facial regard, vague pointing, expressing words and following verbal directions) that were of higher frequency than those with autism but less than those with typical development.

Thus it appears that the children in our sample with PDD, could have been differentiated from their typical developing peers by impairments in their social interactions. The continuum of abnormal social interactions across the autistic spectrum supports these impairments as specific to the disorder. Therefore, careful assessment of social interactions will help identify children with PDD earlier.