How children come to (not) detect and apply multiple functions for objects: Rethinking perseveration and functional fixedness.

Although humans acquire sophisticated and flexible tool-use skills rapidly throughout childhood, young children and adults still show difficulties using the same object for different functions, manifesting in, for example, perseveration or functional fixedness. This paper presents a novel model proposing bottom-up processes taking place during the acquisition of tool-use abilities through active interaction with objects, resulting in two kinds of cognitive representations of an object: a lower-level, action-centered representation and a higher-level, purpose-centered one. In situations requiring the use of an object to attain a goal, the purpose-centered representation is activated quickly, allowing for an immediate detection of suitable tools. In contrast, activation of the action-centered representation is slow and effortful, but comes with the advantage of offering wide-ranging information about the object's features and how they can be applied. This differential availability and activation of action-centered versus purpose-centered representations also contributes to a deeper understanding of the cognitive mechanisms underlying perseveration or functional fixedness during multifunctional tool use. When applied to the teaching and acquisition of tool use, the model indicates that the form in which object-related information is provided determines which of the two object representations is fostered, thereby either facilitating or complicating the flexible application of an object as a tool for different functions.

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.