Baboon (Papio anubis) chimeric face processing by human (Homo sapiens) judges: Influence of stimuli complexity on the perception of oro-facial asymmetries.

Two methodologies have traditionally been used to measure hemispheric specialization for perception and expression of emotions in human and nonhuman primates. The first refers to objective measures, that is, measures of area and length of facial features, and the second concerns subjective "measures," that is, assessment of chimeric faces by human judges. We proposed a refined approach to the subjective assessment of hemispheric specializations, which aims at delimiting methodological issues in the study of orofacial asymmetries. The study focused on a baboon threat orofacial expression, which has led to discordant results according to the methodology used (Wallez & Vauclair, 2011, 2013). We presented human participants with two sets of chimeric stimuli varying the regions of the face likely to be processed. The whole face set was composed of classical chimeric faces, and the upper face set was made of chimeric faces for which the lower part was blurred. The purpose of this new procedure was to shed light on the perception process of baboon faces by human participants during a free-viewing chimeric task. Results showed a concomitant influence of the chimera structure depending on the order of the presentation of the set, revealing a training effect in our human judges. These factors combined together allowed the appearance of an overall left-left chimeric choice by human judges (i.e., which indicates a right hemisphere involvement in baboon threat expression). These findings bring novel insights into the study of orofacial asymmetries in nonhuman primates by human judgments. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Human (Homo sapiens) and baboon (Papio papio) chimeric face processing: right-hemisphere involvement.

[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.

Contrast of hemispheric lateralization for oro-facial movements between learned attention-getting sounds and species-typical vocalizations in chimpanzees: extension in a second colony.

Studies involving oro-facial asymmetries in nonhuman primates have largely demonstrated a right hemispheric dominance for communicative signals and conveyance of emotional information. A recent study on chimpanzee reported the first evidence of significant left-hemispheric dominance when using attention-getting sounds and rightward bias for species-typical vocalizations (Losin, Russell, Freeman, Meguerditchian, Hopkins & Fitch, 2008). The current study sought to extend the findings from Losin et al. (2008) with additional oro-facial assessment in a new colony of chimpanzees. When combining the two populations, the results indicated a consistent leftward bias for attention-getting sounds and a right lateralization for species-typical vocalizations. Collectively, the results suggest that both voluntary-controlled oro-facial and gestural communication might share the same left-hemispheric specialization and might have coevolved into a single integrated system present in a common hominid ancestor.

First evidence of population-level oro-facial asymmetries during the production of distress calls by macaque (Macaca mulatta) and baboon (Papio anubis) infants.

Infant distress calls are vocal communicative signals present in most animals. In nonhuman primates, they correspond to critical vocalizations for caregiving and contribute to the socio-emotional development of the individual. To our knowledge, no systematic study on the development of oro-facial hemispheric specialization in nonhuman primates infants is available. Thus, we proposed to assess to what extend emotional behaviors underlying distress calls in macaques and in baboons younger than 1 year of age may express lateralization. For the first time, a population-level cerebral lateralization was found for screaming and cooing calls in macaques and for the moaning call in baboons. However, differences in patterns of lateralization were found between the two vocalizations produced by macaques (for cooing, the left-side of the mouth opened widest than the right one and for screaming, a preference toward the right side of the mouth was noticed) as well as a sex effect for cooing. Our findings are discussed within the comparative literature in order to comprehend the ontogenetic and phylogenetic changes of hemispheric specialization for emotions in the primate order.

Task complexity, posture, age, sex: which is the main factor influencing manual laterality in captive Cercocebus torquatus torquatus?

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.

Right hemisphere dominance for emotion processing in baboons.

Asymmetries of emotional facial expressions in humans offer reliable indexes to infer brain lateralization and mostly revealed right hemisphere dominance. Studies concerned with oro-facial asymmetries in nonhuman primates largely showed a left-sided asymmetry in chimpanzees, marmosets and macaques. The presence of asymmetrical oro-facial productions was assessed in Olive baboons in order to determine the functional cerebral asymmetries. Two affiliative behaviors (lipsmack, copulation call) and two agonistic ones (screeching, eyebrow-raising) were recorded. For screeching, a strong and significant left hemimouth bias was found, but no significant bias was observed for the other behaviors. These results are discussed in the light of the available literature concerning asymmetrical oro-facial productions in nonhuman primates. In addition, these findings suggest that human hemispheric specialization for emotions has precursors in primate evolution.