No abstract

[Correction Notice: An Erratum for this article was reported in Vol 127(3) of Journal of Comparative Psychology (see record 2013-30238-001). In the article, the link to the supplemental material was not included. Supplemental material for this article is available at: http://dx.doi.org/10.1037/a0031494.supp.] The perception and production of facial expressions have traditionally been used to infer hemispheric specialization for emotions in both human and nonhuman primates. The authors examined orofacial asymmetries in Olive baboons using 2 methodologies. First, objective measures were used to assess hemimouth length and area for screeching and eyebrow-raising. Right-hemisphere specialization was found only for screeching. Second, subjective measures were acquired via a human judgment of the emotional intensity of baboons' chimeric faces for the 2 previous emotional behaviors plus a neutral expression. They also addressed the question of hemispheric lateralization for emotions in human judges by using a chimeric task with human faces. The left-composite chimeric faces of baboons and the human chimeric faces were judged to be emotionally stronger than the right ones for the emotional behaviors, and no preference was found for the neutral non emotional category. Human participants, especially those who displayed a left-hemisphere specialization for processing emotions, demonstrated higher ability to distinguish the most emotionally communicative signals in baboons' facial expressions than right-hemispheric dominant participants. These results are discussed within the theoretical framework of the human and the nonhuman primate literature on hemispheric specialization for perception and production of facial expressions of emotions.

Behavioural asymmetries reflect brain asymmetry in nonhuman primates (NHP) as in humans. By investigating manual laterality, researchers can study the evolution of brain hemisphere specialisation. Three dominant theories aim to establish an evolutionary scenario. The most recent theory relates different levels of manual laterality to task complexity. Our investigation aimed to evaluate the importance of two extrinsic factors (posture and the need for manual coordination) and two intrinsic factors (age and sex) on the expression of manual laterality by red-capped mangabeys. We observed 19 captive-born mangabeys, in spontaneous situations and under experimental conditions (seven experimental tasks varying in complexity). No directionality was observed in hand preference at the group level whatever the task. But our data revealed an effect of task complexity: more subjects were lateralised than not lateralised for the bipedal task and for the three most complex tasks. Finally, we evidenced an age and a sex effect. We compare our results with data for several other primate species and discuss them in the light of different manual laterality theories.