Where is kinship information in the child's face? Signal detection study finds no evidence for lateralization.

Purpose. Dal Martello & Maloney (2006, JOV ) report signal detection experiments measuring the amount of kinship information in the upper and lower halves of children's faces. They found that the upper and lower halves each contained significant information about kinship with the upper half of the face containing considerably more than the lower. The information in the two halves was statistically independent. Previous work has shown that information about age, attractiveness, gender, identity, expression and lip-reading tends to be left-right lateralized. We test whether this is the case for kinship. Methods. 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: 124 adult observers who judged each pair as siblings or not. We summarized performance in each condition by signal detection estimates d\u2032 and \u3b2. Conditions: Full Face visible (FF); Right Half visible (RH); Left Half visible (LH). Different observers participated in each condition. Results. Performance in FF (d\u2032 = 1.079) did not differ significantly (p = n.s.) from performance in RH condition (d\u2032 = 1.024) or from performance in LH (d' = 1.004). Performance in RH and LH did not differ significantly (p = n.s.). The beta values of FF (\u3b2 = 0.888) and RH (\u3b2 = 0.896) did not differ (p = n.s.) and indicated an equal bias towards saying related. The beta for LH (\u3b2 = 1.102) differed significantly (p = 0.0001) from betas on the other conditions. Conclusion. Kinship cues appear to be evenly distributed across the vertical halves of the face and completely redundant. There is no superiority of one or the other side of the observed face for kinship. Observers have a bias against saying 'related' when the right half of the face is masked