Visual lateralization in artiodactyls: A brief summary of research and new evidence on saiga antelope

The visual system and lifestyle characteristics make the even-toed ungulates an excellent model for the studies of behavioural lateralization. Recent research has focused on these mammals providing evidence of lateralization in a wide range of behaviours. This provides an opportunity for the collation of the current theoretical assumptions and the existing empirical evidence for visual lateralization in artiodactyls. In the present study, we aim first to gain a fuller picture of hemispheric specializations in saiga antelopes by investigating the lateralization of vigilance and novel object inspection in the wild. Second, we summarized the results of the research into visual lateralization in even-toed ungulates and attempted to assess the applicability of two popular hypotheses about the division of hemispheric roles. The results on saigas show a significant preference for head turns to the right visual field during vigilance which was more robust in individuals in larger groups. When an unfamiliar artificial object was placed in their natural setting, saigas preferentially viewed it predominantly with the right eye. These results, together with the cumulative evidence in artiodactyls, do not follow either the approach-withdrawal or positivity-negativity dichotomous patterns widely used to explain the division of functions between the hemispheres.

Evolutionary relevance and experience contribute to face discrimination in infant macaques (Macaca mulatta)

In human children and adults, familiar face types-typically own-age and own-species faces-are discriminated better than other face types; however, human infants do not appear to exhibit an own-age bias, but instead better discriminate adult faces, which they see more often. There are two possible explanations for this pattern: Perceptual attunement, which predicts advantages in discrimination for the most-experienced face types; additionally or alternatively, there may be an experience-independent bias for infants to discriminate own-species faces, an adaptation for evolutionarily relevant faces. These possibilities have not been disentangled in studies thus far, which did not control infants' early experiences with faces. In the present study, we tested these predictions in infant macaques (Macaca mulatta) reared under controlled environments, not exposed to adult conspecifics. We measured newborns' (15-25 days; n = 27) and 6- to 7-month-olds' (n = 35) discrimination of human and macaque faces of three ages-young infants, old infants, and adults-in a visual paired comparison task. We found that 6- to 7-month-olds were the best at discriminating adult macaque faces; however, in the first few seconds of looking, additionally discriminated familiar face types-same-aged peer and adult human faces-highlighting the importance of experience with certain face categories. The present data suggest that macaque infants possess both experience-independent and experientially tuned face biases. In human infants, early face skills may likewise be driven by both experience and evolutionary relevance; future studies should consider both of these factors.