How Target Animacy Affects Manual Laterality in Hylobatidae: The First Evidence in Northern White-Cheeked Gibbons (Nomascus leucogenys)

Abstract

Our study presents the first evidence on how target animacy impacts on manual laterality in the Hylobatidae and contributes to filling the knowledge gap between monkeys and great apes in primate evolution of emotional lateralization. Eleven captive individuals of northern white-cheeked gibbons (Nomascus leucogenys) were chosen as focal subjects. There were significantly more ambipreferent individuals than left/righthanded individuals for both inanimate (χ 2 (1, n = 11) = 7.364, p = 0.007) and animate (χ 2 (1, n = 11) = 4.455, p = 0.035) targets, meaning no significant group-level hand preference. The right hand was more frequently used than the left hand for inanimate targets whereas the left hand was more frequently used than the right hand for animate targets, although the interaction between target animacy and hand use was not significant (proportion: F1, 10 = 0.283, p = 0.607; rate: F1, 10 = 0.228, p = 0.643). Our findings in N. leucogenys could not fully support either the tool use theory or the right hemisphere hypothesis.

Eye Preference for Emotional Stimuli in Sichuan Snub-Nosed Monkeys

“…Behavioral laterality, which is believed to be closely related to hemispheric lateralization [Levy, 1977;Rosa Salva et al, 2012], is defined as a preference to employ a preferred limb or sense organ during the process of dealing with various tasks [Ward and Hopkins, 1993;Rogers et al, 2013;Wiper, 2017]. Although it was initially thought that behavioral lateralization was unique to human beings [Porac and Coren, 1981], increasing evidence has been found that behavioral lateralization is commonly seen in both vertebrates and invertebrates [Bisazza et al, 1998;Hopkins, 2007;Frasnelli et al, 2012;Zhao et al, 2015;Rogers and Vallortigara, 2017;Zhao et al, 2019Zhao et al, , 2020. Motor laterality and perception laterality are generally known as 2 main sorts of behavioral laterality, among which the former refers to the lateral behavior related to motor function (e.g., hand and foot preference) while the latter is deemed as the lateral behavior linked to perceptual function (e.g., visual and auditory laterality) [Fitch and Braccini, 2013].…”