Protracted development of stick tool use skills extends into adulthood in wild western chimpanzees.

Tool use is considered a driving force behind the evolution of brain expansion and prolonged juvenile dependency in the hominin lineage. However, it remains rare across animals, possibly due to inherent constraints related to manual dexterity and cognitive abilities. In our study, we investigated the ontogeny of tool use in chimpanzees (Pan troglodytes), a species known for its extensive and flexible tool use behavior. We observed 70 wild chimpanzees across all ages and analyzed 1,460 stick use events filmed in the Taï National Park, Côte d'Ivoire during the chimpanzee attempts to retrieve high-nutrient, but difficult-to-access, foods. We found that chimpanzees increasingly utilized hand grips employing more than 1 independent digit as they matured. Such hand grips emerged at the age of 2, became predominant and fully functional at the age of 6, and ubiquitous at the age of 15, enhancing task accuracy. Adults adjusted their hand grip based on the specific task at hand, favoring power grips for pounding actions and intermediate grips that combine power and precision, for others. Highly protracted development of suitable actions to acquire hidden (i.e., larvae) compared to non-hidden (i.e., nut kernel) food was evident, with adult skill levels achieved only after 15 years, suggesting a pronounced cognitive learning component to task success. The prolonged time required for cognitive assimilation compared to neuromotor control points to selection pressure favoring the retention of learning capacities into adulthood.

Functional fixedness in chimpanzees.

Differences in the tool use of non-human primates and humans are subject of ongoing debate. In humans, representations of object functions underpin efficient tool use. Yet, representations of object functions can lead to functional fixedness, which describes the fixation on a familiar tool function leading to less efficient problem solving when the problem requires using the tool for a new function. In the current study, we examined whether chimpanzees exhibit functional fixedness. After solving a problem with a tool, chimpanzees were less efficient in solving another problem which required using the same tool with a different function compared to a control group. This fixation effect was still apparent after a period of nine months and when chimpanzees had learned about the function of a tool by observation of a conspecific. These results suggest that functional fixedness in our closest living relatives likely exists and cast doubt on the notion that stable function representations are uniquely human.

Tool mastering today - an interdisciplinary perspective.

Tools have coined human life, living conditions, and culture. Recognizing the cognitive architecture underlying tool use would allow us to comprehend its evolution, development, and physiological basis. However, the cognitive underpinnings of tool mastering remain little understood in spite of long-time research in neuroscientific, psychological, behavioral and technological fields. Moreover, the recent transition of tool use to the digital domain poses new challenges for explaining the underlying processes. In this interdisciplinary review, we propose three building blocks of tool mastering: (A) perceptual and motor abilities integrate to tool manipulation knowledge, (B) perceptual and cognitive abilities to functional tool knowledge, and (C) motor and cognitive abilities to means-end knowledge about tool use. This framework allows for integrating and structuring research findings and theoretical assumptions regarding the functional architecture of tool mastering via behavior in humans and non-human primates, brain networks, as well as computational and robotic models. An interdisciplinary perspective also helps to identify open questions and to inspire innovative research approaches. The framework can be applied to studies on the transition from classical to modern, non-mechanical tools and from analogue to digital user-tool interactions in virtual reality, which come with increased functional opacity and sensorimotor decoupling between tool user, tool, and target. By working towards an integrative theory on the cognitive architecture of the use of tools and technological assistants, this review aims at stimulating future interdisciplinary research avenues.

Prior experience mediates the usage of food items as tools in great apes (Pan paniscus, Pan troglodytes, Gorilla gorilla, and Pongo abelii).

Humans use tools with specific functions to solve tasks more efficiently. However, functional specialization often comes at a cost: It can hinder the production of actions that are not usually performed with those tools, thus resulting in a fixation effect (functional fixedness). Little is known about whether our closest living relatives, the nonhuman great apes, are vulnerable to this detrimental effect of experience. We examined whether great apes from 4 species (N = 35) would become fixated on the familiar action with an object. More precisely, some subjects experienced a novel food item (grissini), either whole or broken into pieces, whereas others did not. Then, subjects faced a task that required them to use the food item to rake in an out-of-reach food reward. Results indicated that all 4 species could use a food item as a tool. Apes were more likely to do so in the first trial when they had not experienced the tool as food before, even though they tasted the food before using it as a tool. Orangutans and bonobos used the food item more often as a tool than chimpanzees. A preference test ruled out that performance was dependent on individual or species food preferences. Our results suggest that apes might have represented one object in two different ways (i.e., as "food" and as "tool") and then became fixated on one of these two representations. However, it is unclear whether the fixation occurred because of the item's prior function or its identity. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Object preferences in captive Sumatran orang-utans (Pongo abelii).

While preferences for perceptual features of objects are well studied in humans, little is known about this trait in other great apes. We therefore presented captive Sumatran orang-utans (Pongo abelii) with objects that differed in shape (spherical, cuboid), colour (red, green), or texture (hard, soft). Overall, orang-utans preferred spherical over cuboid and red over green objects. Soft objects were preferred over hard ones. However, this preference might be confounded by the decomposable characteristic of soft objects since the orang-utans often unwrapped them. This study shows object preferences in orang-utans similar to those in humans, suggesting that perceptual preferences for basic object features such as shape and colour may be shared across primate species.

Innovative problem solving in great apes: the role of visual feedback in the floating peanut task.

Nonhuman great apes show remarkable behavioural flexibility. Some individuals are even able to use water as a tool: They spit water into a vertical tube to make a peanut float upwards until it comes into reach (floating peanut task; FPT). In the current study, we used the FPT to investigate how visual feedback, an end-state demonstration and a social demonstration affect task performance in nonhuman great apes in three experiments. Our results indicate that apes who had acquired the solution with a clear tube maintained it with an opaque one. However, apes starting with an opaque tube failed to solve the task. Additionally, facing the peanut floating on a water-filled tube (i.e., an end-state demonstration) promoted success independent on the availability of visual feedback. Moreover, experiencing how water was poured into the tube either by a human demonstrator or by a water tap that had been opened either by the ape or a human did not seem to be of further assistance. First, this study suggests that great apes require visual feedback for solving the FPT, which is no longer required after the initial acquisition. Second, some subjects benefit from encountering the end-state, a finding corroborating previous studies.

How prior experience and task presentation modulate innovation in 6-year-old-children.

Low innovation rates have been found with children until 6-8 years of age in tasks that required them to make a tool. Little is known about how prior experience and task presentation influence innovation rates. In the current study, we investigated these aspects in the floating peanut task (FPT), which required children to pour water into a vertical tube to retrieve a peanut. In three experiments, we varied the amount of plants that 6-year-olds (N = 256) watered prior to the task (zero, one, or five plants), who watered the plants (child or experimenter), and the distance and salience of the water source. We expected that prior experience with the water would modulate task performance by either boosting innovation rates (facilitation effect) or reducing them given that children would possibly learn that the water was for watering plants (functional fixedness effect). Our results indicate robustly low innovation rates in 6-year-olds. However, children's performance improved to some extent with increased salience of the water source as well as with an experimenter-given hint. Due to the low innovation rates in this age group, we investigated whether watering plants prior to the FPT would influence innovation rates in 7- and 8-year-olds (N = 33), for which we did not find evidence. We conclude that 6-year-olds struggle with innovation but that they are more likely to innovate if crucial aspects of the task are made more salient. Thus, although 6-year-olds can innovate, they require more physical and social scaffolding than older children and adults.