Cenni Camilla, Casarrubea Maurizio, Gunst Noëlle, Vasey Paul L, Pellis Sergio M, Wandia I Nengah, Leca Jean-Baptiste
Department of Psychology, University of Lethbridge, Lethbridge, AB, Canada.
Department of Biomedicine, Neuroscience and Advanced Diagnostics (Bi.N.D.), Human Physiology Section "Giuseppe Pagano", School of Medicine of Palermo, Palermo, Italy.
Physiol Behav. 2020 Aug 1;222:112938. doi: 10.1016/j.physbeh.2020.112938. Epub 2020 May 15.
Inferring functional components of behavioral sequences is a crucial but challenging task. A systematic comparison of their temporal structure is a good starting point, based on the postulate that more functional traits are less structurally variable. We studied stone handling behavior (SH) in Balinese long-tailed macaques, a versatile form of stone-directed play. We tested the hypothesis that stones are used by male monkeys to stimulate their genitals in a sexual context (i.e., "sex toy" hypothesis). Specifically, two SH actions (i.e., "tap-on-groin" (TOG) and "rub-on-groin" (ROG), respectively the repetitive tapping and rubbing of a stone onto the genital area) gained functional properties as self-directed tool-assisted masturbation. Owing to the structural organization of playful activities, we predicted that SH sequences without TOG/ROG would exhibit higher levels of variability, repeatability and exaggeration than SH sequences with TOG/ROG. We also predicted that TOG/ROG would occur more often and last longer in SH sequences in which penile erection - a sexually-motivated physiological response in primates - was observed than in SH sequences in which penile erection was not observed. To identify and compare recurring series of SH patterns otherwise undetectable by using conventional quantitative approaches across SH sequences containing TOG/ROG or not, we used a temporal analysis known as "T-pattern detection and analysis" (TPA). Our predictions about variability, exaggeration and temporal association between TOG/ROG in males and penile erection were supported. As expected, SH sequences without TOG/ROG were, on average, more repeatable than SH sequences with TOG/ROG, but the difference was not statistically significant. Overall, the "sex toy" hypothesis was partly supported, and our results suggested that TOG and ROG are two forms of tool-assisted genital stimulation, possibly derived from the playful handling of stones. These findings are consistent with the view that tool use may evolve in stages from initially non-functional object manipulation, such as object play.
推断行为序列的功能组成部分是一项至关重要但具有挑战性的任务。基于功能特征越多结构变异性越小的假设，对其时间结构进行系统比较是一个很好的起点。我们研究了巴厘岛长尾猕猴的玩石行为（SH），这是一种形式多样的指向石头的玩耍行为。我们检验了一个假设，即雄性猴子在性情境中使用石头刺激生殖器（即“性玩具”假设）。具体而言，两种SH行为（即“轻拍腹股沟”（TOG）和“摩擦腹股沟”（ROG），分别是将石头反复轻拍和摩擦到生殖器区域）具有作为自我导向的工具辅助自慰的功能特性。由于玩耍活动的结构组织，我们预测没有TOG/ROG的SH序列将比有TOG/ROG的SH序列表现出更高水平的变异性、重复性和夸张性。我们还预测，在观察到阴茎勃起（灵长类动物的一种性动机生理反应）的SH序列中，TOG/ROG会比在未观察到阴茎勃起的SH序列中更频繁出现且持续时间更长。为了识别和比较在包含或不包含TOG/ROG的SH序列中使用传统定量方法无法检测到的反复出现的SH模式系列，我们使用了一种称为“T模式检测与分析”（TPA）的时间分析方法。我们关于变异性、夸张性以及雄性中TOG/ROG与阴茎勃起之间时间关联的预测得到了支持。正如预期的那样，没有TOG/ROG的SH序列平均比有TOG/ROG的SH序列更具重复性，但差异没有统计学意义。总体而言，“性玩具”假设得到了部分支持，我们的结果表明TOG和ROG是两种工具辅助的生殖器刺激形式，可能源自对石头的玩耍性操作。这些发现与工具使用可能从最初的非功能性物体操纵（如物体玩耍）分阶段演变的观点一致。
