Gestural communication permeates all domains of chimpanzees' social life and is intentional in use. However, we still have only limited information on how young apes develop the sociocognitive skills needed for intentional communication. In this cross-sectional study, we document the development of behavioral adjustment to the recipient's visual attention—considered a hallmark of intentional communication—in wild immature chimpanzees' gestural communication. We studied 11 immature chimpanzees (Pan troglodytes schweinfurthii): three infants, four juveniles, and four adolescents gesturing towards their mother. We quantified silent-visual, audible, and contact gestures indexed to maternal visual attention and inattention. We investigated unimodal adjustment, defined by the capacity of young chimpanzees to deploy fewer silent-visual signals when their mothers did not show full visual attention towards them as compared with when they did. We then examined cross-modal adjustment, defined as the capacity of chimpanzees to deploy more audible-or-contact gestures than silent-visual gestures in the condition where their mothers did not show full visual attention as compared to when they did. Our results show a gradual decline in the use of silent-visual gestures when the mother is not visually attentive with increasing age. The absence of silent-visual gesture production toward a visually inattentive recipient (complete unimodal adjustment) was not fully in place until adolescence. Immature chimpanzees used more audible-or-contact gestures than silent-visual ones when their mothers did not show visual attention and vice-versa when they did. This cross-modal adjustment was expressed in juveniles and adolescents but not in infants. Overall, this study shows that infant chimpanzees were limited in their sensitivity to maternal attention when gesturing, whereas adolescent chimpanzees adjusted their communication appropriately. Juveniles present an intermediate pattern with cross-modal adjustment preceding unimodal adjustment and with variability in the age of onset.

中文翻译：

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对交流伙伴注意力状态的敏感性：野生黑猩猩母婴二元组的发育研究（Pan troglodytes schweinfurthii）

手势交流渗透到黑猩猩社会生活的所有领域，并且是有意使用的。然而，关于年幼的类人猿如何发展有意交流所需的社会认知技能，我们仍然只有有限的信息。在这项横断面研究中，我们记录了在野生未成熟黑猩猩的手势交流中对接受者视觉注意力的行为调整的发展——被认为是有意交流的标志。我们研究了 11 只未成熟的黑猩猩 ( Pan troglodytes schweinfurthii )：3 只婴儿、4 只幼年和 4 只指向母亲的青少年。我们量化了与母体视觉注意力和注意力不集中相关的无声视觉、听觉和接触手势。我们研究了单峰调整，定义为与母亲相比，当他们的母亲没有对他们表现出完全的视觉注意力时，年轻的黑猩猩部署更少的无声视觉信号的能力。然后，我们检查了跨模态调整，定义为黑猩猩在母亲没有表现出完全视觉注意力的情况下，与他们相比，它们比无声视觉手势部署更多的听觉或接触手势的能力。我们的研究结果表明，当母亲随着年龄的增长而视觉注意力不集中时，无声视觉手势的使用逐渐减少。对视觉注意力不集中的接受者没有无声的视觉手势产生（完全单峰调整）直到青春期才完全到位。当它们的母亲没有表现出视觉注意时，未成熟的黑猩猩会使用更多的听觉或接触手势而不是无声视觉的手势，反之亦然。这种跨模式调整在青少年和青少年中表达，但在婴儿中没有。总体而言，这项研究表明，婴儿黑猩猩在做手势时对母亲注意的敏感性有限，而青少年黑猩猩则适当地调整了他们的交流。青少年呈现出一种中间模式，在单峰调整之前有跨模式调整，并且发病年龄存在变异性。