Ben Kenward

Development of tool use in New Caledonian crows: inherited action patterns and social influences

New Caledonian crows, Corvus moneduloides, are the most advanced avian tool makers and tool users. We previously reported that captive-bred isolated New Caledonian crows spontaneously use twig tools and cut tools out of Pandanus spp. tree leaves, an activity possibly under cultural influence in the wild. However, what aspects of these behaviours are inherited and how they interact with individual and social experience remained unknown. To examine the interaction between inherited traits, individual learning and social transmission, we observed the ontogeny of twig tool use in hand-reared juveniles. Successful food retrieval was preceded by stereotyped object manipulation action patterns that resembled components of the mature behaviour, demonstrating that tool-oriented behaviours in this species are an evolved specialization. However, there was also an effect of social learning: juveniles that had received demonstrations of twig tool use by their human foster parent showed higher levels of handling and insertion of twigs than did their naive counterparts; a choice experiment showed that they preferred to handle objects that they had seen being manipulated by their human foster parent. Our observations are consistent with the hypothesis that individual learning, cultural transmission and creative problem solving all contribute to the acquisition of the tool-oriented behaviours in the wild, but inherited species-typical action patterns have a greater role than has been recognized.

Over-imitation is better explained by norm learning than by distorted causal learning

In over-imitation, children copy even elements of a goal-directed action sequence that appear unnecessary for achieving the goal. We demonstrate in 4-year olds that the unnecessary action is specifically associated with the goal, not generally associated with the apparatus. The unnecessary action is performed flexibly: 4-year olds usually omit it if it has already been performed by an adult. Most 5-year olds do not verbally report the unnecessary action as necessary when achieving the goal, although most of them report an equivalent but necessary action as necessary. Most 5-year olds explain the necessary action in functional terms, but are unsure as to the function of the unnecessary action. These verbal measures do not support the hypothesis that children over-imitate primarily because they encode unnecessary actions as causing the goal even in causally transparent systems. In a causally transparent system, explanations for over-imitation fitting the results are that children are ignorant of the unnecessary actions purpose, and that they learn a prescriptive norm that it should be carried out. In causally opaque systems, however, for children and for adults, any action performed before achieving the goal is likely to be inferred as causally necessary—this is not over-imitation, but ordinary causal learning.

Over-imitating preschoolers believe unnecessary actions are normative and enforce their performance by a third party

Over-imitation, which is common in children, is the imitation of elements of an action sequence that are clearly unnecessary for reaching the final goal. A variety of cognitive mechanisms have been proposed to explain this phenomenon. Here, 48 3- and 5-year-olds together with a puppet observed an adult demonstrate instrumental tasks that included an unnecessary action. Failure of the puppet to perform the unnecessary action resulted in spontaneous protest by the majority of the children, with some using normative language. Children also protested in comparison tasks in which the puppet violated convention or instrumental rationality. Protest in response to the puppets omission of unnecessary action occurred even after the puppets successful achievement of the goal. This observation is not compatible with the hypothesis that the primary cause of over-imitation is that children believe the unnecessary action causes the goal. There are multiple domains that children may believe determine the unnecessary actions normativity, two being social convention and instrumental rationality. Because the demonstration provides no information about which domains are relevant, children are capable of encoding apparently unnecessary action as normative without information as to which domain determines the unnecessary actions normativity. This study demonstrates an early link between two processes of fundamental importance for human culture: faithful imitation and the adherence to and enforcement of norms.

Preschoolers Distribute Scarce Resources According to the Moral Valence of Recipients' Previous Actions.

Children aged 3 years and 4½ years old watched a puppet, struggling to achieve goals, who was helped by a 2nd puppet and violently hindered by a 3rd. The children then distributed wooden biscuits between the helper and hinderer. In Experiment 1, when distributing a small odd number of biscuits, 4½-year-olds (N = 16) almost always gave more to the helper. Children verbally justified their unequal distributions by reference to the helpers prosocial behavior or the hinderers antisocial behavior. In Experiment 2, when biscuits were more plentiful, 4½-year-olds (N = 16) usually gave equal numbers to helper and hinderer, indicating that 4½-year-olds usually preferred not to distribute unequally unless forced to by resource scarcity. Three-year-olds (N = 16 in Experiment 1, N = 20 in Experiment 3) gave more biscuits equally often to the helper and to the hinderer. In many cases, this was because they were confused as to the identities and actions of the puppets, possibly because they were shocked by the hinderers actions. Two fundamental moral behaviors are therefore demonstrated in young preschoolers: indirect reciprocity of morally valenced acts and a preference for equality when distributing resources, although the cognitive bases for these behaviors remain unclear. These results join other recent studies in demonstrating that the seeds of complex moral understanding and behavior are found early in development.

Lateralization of tool use in New Caledonian crows (Corvus moneduloides)

We studied laterality of tool use in 10 captive New Caledonian (NC) crows (Corvus moneduloides). All subjects showed near–exclusive individual laterality, but there was no overall bias in either direction (five were left–lateralized and five were right–lateralized). This is consistent with results in non–human primates, which show strong individual lateralization for tool use (but not for other activities), and also with observations of four wild NC crows by Rutledge & Hunt. Jointly, these results contrast with observations that the crows have a population–level bias for manufacturing tools from the left edges of Pandanus sp. leaves, and suggest that the manufacture and use of tools in this species may have different neural underpinnings.

Goal Directedness and Decision Making in Infants.

The term goal directed conventionally refers to either of 2 separate process types-motor processes organizing action oriented toward physical targets and decision-making processes that select these targets by integrating desire for and knowledge of action outcomes. Even newborns are goal directed in the first sense, but the status of infants as decision makers (the focus here) is unknown. In this study, 24-month-olds learned to retrieve an object from a box by pressing a button, and then the objects value was increased. After the objects subsequent disappearance, these children were more likely to press the button to try to retrieve the object than were control 24-month-olds who had learned to retrieve the object but for whom the objects value was unchanged. Such sensitivity to outcome value when selecting actions is a hallmark of decision making. However, 14- and 19-month-olds showed no such sensitivity. Possible explanations include that they had not learned the specifics of the action outcome; they had not acquired the necessary desire; or they had acquired both but did not integrate them to make a decision.

Infants help a non-human agent.

Young children can be motivated to help adults by sympathetic concern based upon empathy, but the underlying mechanisms are unknown. One account of empathy-based sympathetic helping in adults states that it arises due to direct-matching mirror-system mechanisms which allow the observer to vicariously experience the situation of the individual in need of help. This mechanism could not account for helping of a geometric-shape agent lacking human-isomorphic body-parts. Here 17-month-olds observed a ball-shaped non-human agent trying to reach a goal but failing because it was blocked by a barrier. Infants helped the agent by lifting it over the barrier. They performed this action less frequently in a control condition in which the barrier could not be construed as blocking the agent. Direct matching is therefore not required for motivating helping in infants, indicating that at least some of our early helpful tendencies do not depend on human-specific mechanisms. Empathy-based mechanisms that do not require direct-matching provide one plausible basis for the observed helping. A second possibility is that rather than being based on empathy, the observed helping occurred as a result of a goal-contagion process in which the infants were primed with the unfulfilled goal.

Four-year-olds’ strategic allocation of resources: Attempts to elicit reciprocation correlate negatively with spontaneous helping

Behaviour benefitting others (prosocial behaviour) can be motivated by self-interested strategic concerns as well as by genuine concern for others. Even in very young children such behaviour can be motivated by concern for others, but whether it can be strategically motivated by self-interest is currently less clear. Here, children had to distribute resources in a game in which a rich but not a poor recipient could reciprocate. From four years of age participants strategically favoured the rich recipient, but only when recipients had stated an intention to reciprocate. Six- and eight-year-olds distributed more equally. Children allocating strategically to the rich recipient were less likely to help when an adult needed assistance but was not in a position to immediately reciprocate, demonstrating consistent cross-task individual differences in the extent to which social behaviour is self- versus other-oriented even in early childhood. By four years of age children are capable of strategically allocating resources to others as a tool to advance their own self-interest.

A Computational Model of Social-Learning Mechanisms

In this article we propose a computational model that describes how observed behavior can influence an observer’s own behavior, including the acquisition of new task descriptions. The sources of influence on our model’s behavior are: beliefs about the world’s possible states and actions causing transitions between them; baseline preferences for certain actions; a variable tendency to infer and share goals in observed behavior; and a variable tendency to act efficiently to reach rewarding states. Acting on these premises, our model is able to replicate key empirical studies of social learning in children and chimpanzees. We demonstrate how a simple artificial system can account for a variety of biological social transfer phenomena, such as goal-inference and over-imitation, by taking into account action constraints and incomplete knowledge about the world dynamics.

Enactment of third-party punishment by 4-year-olds

When prompted, preschoolers advocate punishment for moral transgressions against third parties, but little is known about whether and how they might act out such punishment. In this study, adult demonstrators enacted doll stories in which a perpetrator child doll made an unprovoked attack on a victim child doll, after which an adult doll punished either the perpetrator (consistent punishment) or victim (inconsistent punishment). When asked to help retell the story, given free choice of their own preferred actions for the adult doll, 4-year-olds (N = 32) were influenced by the demonstrated choice of target when selecting a target for punishment or admonishment. This influence was weak following inconsistent punishment, however, because the participants tended to change the story by punishing or admonishing the perpetrator when the demonstrator had punished the victim. Four-year-olds’ tendency to select a moral rule violator as a target for punishment is therefore stronger than their tendency to copy the specific actions of adults, which itself is known to be very strong. The evidence suggests that 4-year-olds’ enactment of punishment is at least partially based on a belief that antisocial actions deserve to be punished.