Rational action selection in 1½- to 3-year-olds following an extended training experience

Context-Specificity of Locomotor Learning Is Developed during Childhood

Humans can perform complex movements with speed and agility in the face of constantly changing task demands. To accomplish this, motor plans are adapted to account for errors in our movements because of changes in our body (e.g., growth or injury) or in the environment (e.g., walking on sand vs ice). It has been suggested that adaptation that occurs in response to changes in the state of our body will generalize across different movement contexts and environments, whereas adaptation that occurs with alterations in the external environment will be context-specific. Here, we asked whether the ability to form generalizable versus context-specific motor memories develops during childhood. We performed a cross-sectional study of context-specific locomotor adaptation in 35 children (3-18 years old) and 7 adults (19-31 years old). Subjects first adapted their gait and learned a new walking pattern on a split-belt treadmill, which has two belts that move each leg at a different speed. Then, subjects walked overground to assess the generalization of the adapted walking pattern across different environments. Our results show that the generalization of treadmill after-effects to overground walking decreases as subjects' age increases, indicating that age and experience are critical factors regulating the specificity of motor learning. Our results suggest that although basic locomotor patterns are established by two years of age, brain networks required for context-specific locomotor learning are still being developed throughout youth.

Homo imitans? Seven reasons why imitation couldn't possibly be associative

Many comparative and developmental psychologists believe that we are Homo imitans; humans are more skilled and prolific imitators than other animals, because we have a special, inborn 'intermodal matching' mechanism that integrates representations of others with representations of the self. In contrast, the associative sequence learning (ASL) model suggests that human infants learn to imitate using mechanisms that they share with other animals, and the rich resources provided by their sociocultural environments. This article answers seven objections to the ASL model: (i) it presents evidence that newborns do not imitate; (ii) argues that infants receive a plentiful supply of the kind of experience necessary for learning to imitate; (iii) suggests that neither infants nor adults can imitate elementally novel actions; (iv) explains why non-human animals have a limited capacity for imitation; (v) discusses the goal-directedness of imitation; (vi) presents evidence that improvement in imitation depends on visual feedback; and (vii) reflects on the view that associative theories steal 'the soul of imitation'. The empirical success of the ASL model indicates that the mechanisms which make imitation possible, by aligning representations of self with representations of others, have been tweaked by cultural evolution, not built from scratch by genetic evolution.

Which way to take? Infants select an efficient path to their goal

In two experiments, we examined the development of the ability to select efficient means in order to attain a goal in 1.5- and 2-year-olds (N = 79) using a setup in which two paths led to a goal. One of the paths was shorter, and thus more efficient, than the other path. Experiment 1 showed a strong tendency in both age groups to choose the shorter path. In Experiment 2, the shorter path was initially blocked and became available only after infants repeatedly took the longer path. Children demonstrated increasing use of the more efficient path over time. The results of both experiments point to some abilities of efficient action selection in infants.

Impaired acquisition of goal-directed action in healthy aging

According to dual-system theories, instrumental learning is supported by dissociable goal-directed and habitual systems. Previous investigations of the dual-system balance in healthy aging have yielded mixed results. To further investigate this issue, we compared performance of young (17-24 years) and older (69-84 years) adults on an instrumental learning task. Following the initial learning phase, the behavioral autonomy of the motivational significance of the instrumental outcome was assessed with an outcome-devaluation test and slips-of-action test. The present study provides evidence for a disrupted dual-system balance in healthy aging, as reflected in reduced outcome-induced conflict during acquisition, as well as in impaired performance during the test stage, during which participants had to flexibly adjust their actions to changes in the current desirability of the behavioral outcome. These findings will be discussed in relation to previous aging studies into habitual and goal-directed control, as well as other cognitive impairments, challenges that older adults may face in everyday life, and to the neurobiological basis of the developmental pattern of goal-directed action across the lifespan.

The image-scratch paradigm: a new paradigm for evaluating infants' motivated gaze control

Human infants show spontaneous behaviours such as general movement, goal-directed behaviour, and self-motivated behaviour from a very early age. However, it is unclear how these behaviours are organised throughout development. A major hindrance to empirical investigation is that there is no common paradigm for all ages that can circumvent infants' underdeveloped verbal and motor abilities. Here, we propose a new paradigm, named the image-scratch task, using a gaze-contingent technique that is adaptable to various extents of motor ability. In this task, participants scratch off a black layer on a display to uncover pictures beneath it by using their gaze. We established quantitative criteria for spontaneous eye-movement based on adults' gaze-data and demonstrated that our task is useful for evaluating eye-movements motivated by outcome attractiveness in 8-month-olds. Finally, we discuss the potential of this paradigm for revealing the mechanisms and developmental transitions underlying infants' spontaneous and intentional behaviours.

Event-related potentials to intact and disrupted actions in children and adults

The current research used event-related potentials (ERPs) to investigate neurophysiological responses to intact and disrupted actions embedded within an event in children and adults. Responses were recorded as children (24-month-olds) and adults observed a relatively novel event composed of three actions. In one condition pauses were inserted at intact boundaries (i.e., at the endpoint of each action), whereas in the other condition they were inserted at breakpoints that disrupted the action (i.e., in the middle of each action). Evoked responses revealed differences across conditions in both groups; disrupted actions elicited a prolonged negative slow wave from 100 to 700 ms in children, whereas adults demonstrated two distinct negative peaks between 50-150 and 250-350 ms. These findings contribute the first electrophysiological evidence that children readily detect disruptions to ongoing events by the end of the second year, even with limited exposure to the event itself. Furthermore, they suggest that adults rely on two distinct mechanisms when processing novel events. Results are discussed in relation to the role of perceptual and conceptual levels of analysis in the development of action processing.

Early rationality in action perception and production? A theoretical exposition

Within recent years, the question of early rationality in action perception and production has become a topic of great interest in developmental psychology. On the one hand, studies have provided evidence for rational action perception and action imitation even in very young infants. On the other hand, scholars have recently questioned these interpretations and proposed that the ability to rationally evaluate actions is not yet in place in infancy. Others have examined the development of the ability to make rational action choices and have indicated limitations of young children's ability to act rationally. This editorial to the special issue on Early Rationality in Action Perception and Production? introduces the reader to the current debate. It elucidates the underlying theoretical assumptions that drive the debate on whether or not young children's action perception and production is rational. Finally, it summarizes the papers and their contributions to the theoretical debate.

Resolution of outcome-induced response conflict by humans after extended training

Studies of incongruent discrimination learning, where the outcome event of one response acts as the discriminative stimulus for the opposite response, suggest that humans rely on habitual stimulus-response (S-R) associations when outcome-response (O-R) associations would cause response conflict. Here, two experiments were conducted to investigate the robustness of this habitual strategy. In Experiment 1, we found that extensive instrumental discrimination training supported learning about the incongruent R → O contingencies, as assessed by an outcome devaluation test. Differential representations of the stimulus and the (associatively retrieved) outcome may have allowed for goal-directed incongruent performance. Experiment 2 failed to provide evidence for this possibility; direct presentation as well as associative retrieval of the incongruent events (by Pavlovian stimuli) activated the response that was associated with each event in its role of stimulus as opposed to outcome. We did find that participants successfully acquired explicit knowledge of the incongruent contingencies, which raises the possibility that propositional encoding allowed them to overcome the response conflict caused by O-R associations. Alternative associative and propositional accounts of successful goal-directed incongruent performance with extensive training will be discussed.