Synchronized practice helps bearded capuchin monkeys learn to extend attention while learning a tradition

Abstract

Culture extends biology in that the setting of development shapes the traditions that individuals learn, and over time, traditions evolve as occasional variations are learned by others. In humans, interactions with others impact the development of cognitive processes, such as sustained attention, that shape how individuals learn as well as what they learn. Thus, learning itself is impacted by culture. Here, we explore how social partners might shape the development of psychological processes impacting learning a tradition. We studied bearded capuchin monkeys learning a traditional tool-using skill, cracking nuts using stone hammers. Young monkeys practice components of cracking nuts with stones for years before achieving proficiency. We examined the time course of young monkeys' activity with nuts before, during, and following others' cracking nuts. Results demonstrate that the onset of others' cracking nuts immediately prompts young monkeys to start handling and percussing nuts, and they continue these activities while others are cracking. When others stop cracking nuts, young monkeys sustain the uncommon actions of percussing and striking nuts for shorter periods than the more common actions of handling nuts. We conclude that nut-cracking by adults can promote the development of sustained attention for the critical but less common actions that young monkeys must practice to learn this traditional skill. This work suggests that in nonhuman species, as in humans, socially specified settings of development impact learning processes as well as learning outcomes. Nonhumans, like humans, may be culturally variable learners.

Keywords: attention; development; learning; primates; tool use.

Fig. 1.

An adult bearded capuchin monkey has cracked a palm nut using a stone hammer on a log anvil and is removing and eating pieces of the kernel. A young monkey that cannot crack a nut itself watches closely. Image used with permission from Luca Antonio Marino, Roma Tre University (Rome, Italy).

Fig. 2.

Probability that a young monkey (n = 11) manipulated a nut in the 1 min before the onset of striking a nut performed by another monkey (No cracking) and during each of the 5 min following the onset of striking a nut by another monkey. The boxes display the median and interquartile range, and whiskers indicate minimum and maximum values. The solid line within the box depicts the median. Circles indicate values of outliers.

Fig. 3.

Rate per 10 min of manipulation of nuts by young monkeys (n = 16) when one or more other monkeys struck nuts (Cracking present) during each of the 7 min after others stopped striking a nut and in periods 8 min or longer after others stopped striking a nut (8 min or over). The exponential curve generated by model fitting is overlaid. The boxes display the median and interquartile range, and whiskers indicate minimum and maximum values. The solid line within the box depicts the median. Circles indicate values of outliers. The half-life of the decline occurred at 2.1 min.

Fig. 4.

Probability that a young monkey (n = 11) percussed a nut 1 min before the onset of striking a nut performed by another monkey (No cracking) and during each of the 5 min following the onset of striking a nut by another monkey. The boxes display the median and interquartile range, and whiskers indicate minimum and maximum values. The solid line within the box depicts the median. Circles indicate values of outliers.

Fig. 5.

Rate of direct percussion of nuts by young monkeys (n = 16) when one or more other monkeys struck nuts (Cracking present) during the 7 min after other monkeys stopped striking nuts and in periods 8 min or longer after others stopped striking a nut (8 min or over). The boxes display the median and interquartile range; whiskers indicate minimum and maximum values. The solid line depicts the median. Circles indicate values of outliers. The exponential curve generated by model fitting is overlaid. The half-life of the decline occurred at 0.62 min.

Fig. 6.

Rate of striking a nut with a stone by young monkeys (n = 16) when one or more monkeys in the group struck nuts (Cracking present) during the 7 min after other monkeys stopped striking and in periods 8 min or longer after others stopped striking a nut (8 min or over). The boxes display the median and interquartile range, and whiskers indicate minimum and maximum values. The solid line depicts the median. The exponential curve generated by model fitting is overlaid. Circles indicate values of outliers.

Fig. 7.

Percentage of time spent within an arm’s length of an anvil by young monkeys (n = 16) when one or more other monkeys struck nuts (Cracking present) during the 7 min after other monkeys stopped striking and in periods 8 min or longer after others stopped striking a nut (8 min or over). The boxes display the median and interquartile range, and whiskers indicate minimum and maximum values. The solid line depicts the median. Circles indicate values of outliers. The exponential curve generated by model fitting is overlaid. The half-life of the decline occurred at 2.8 min.