Objectives: To compare infant siblings of children with autism (ASD sibs) and infant siblings of typically developing children (TD sibs) with respect to attention and rated emotional valence (affect) during interaction with a parent, and subsequent joint attention with an examiner.

Methods: 17 ASD and 17 TD sibs (both groups split almost evenly by gender) interacted with their parents in a face-to-face/still-face (FFSF) procedure at six months. A slightly smaller number of siblings participated in the Early Social Communication Scales (ESCS) at 8, 10, 12, 15, and 18 months. Coding was standard except that emotional valence was rated by non-expert students to determine if potential deficits were perceivable by untrained individuals.

Results: Male ASD sibs were rated as expressing more negative (less positive) emotional valence than male TD sibs in the FFSF. As a whole, the mean duration of ASD sibs' gazes directed away from their parents' faces were longer than those of TD sibs. ASD sibs also exhibited less frequent shifts between gazing at and away from the parent's face. Gaze shift frequency was positively associated with initiating joint attention in the ESCS. ASD Sibs showed deficits in initiating joint attention and responding to joint attention in the ESCS between 8 & 18 months.

Conclusions: The results suggest male-specific attenuations of positive affect in ASD sibs, consonant with the heightened risk status of these boys. ASD sibs show a general pattern of difficulty in disengaging from non-social stimuli at 6 months. This difficulty may be manifested between 8 & 18 months as a reduction in initiating and responding to joint attention (both of which require disengaging from a non-social stimulus).