Where are kin recognition cues in the face?

Observers accurately judge children's degree of kinship given facial photographs (Dal Martello & Maloney, VSS2002). We report two experiments intended to determine where in the face the cues signalling kinship fall. Since the upper face changes less than the lower during development (Enlow & Hans, 1996), we hypothesized that observers would rely on age-invariant features in the upper face. Stimuli:30 pairs of photographs, each photograph portraying a child's face with background removed. Half were of siblings, half, unrelated. The children's ages spanned 14 years. Observers: 220 observers judged each pair as siblings or not. We summarized performance in each condition by signal detection d' estimates. Experiment 1 Conditions: Full Face visible (FF); Upper Half face visible (UH); Lower Half face visible (LH). Different observers participated in each condition. Results: Performance in FF (d' = 1.19) and in UH condition (d''=1.12) did not differ significantly (p = n.s.). Performance in LH (d' = 0.41) was significantly lower (p < 0.0001) than that in other conditions.