Edited by: Ivan Toni, Radboud University, Netherlands
Reviewed by: Birgit Elsner, Universität Potsdam, Germany; Maria Gräfenhain, Georg-August-Universität Göttingen, Germany
*Correspondence: Marlene Meyer, Donders Institute for Brain, Cognition and Behaviour, Radboud University, P.O. Box 9104, 6500 HE Nijmegen, Netherlands. e-mail:
This is an open-access article subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.
When acting jointly with others, adults can be as proficient as when acting individually. However, how young children coordinate their actions with another person and how their action coordination develops during early childhood is not well understood. By means of a sequential button-pressing game, which could be played jointly or individually, the action coordination of 2½- and 3-year-old children was examined. Performance accuracy and variability of response timing were taken as indicators of coordination ability. Results showed substantial improvement in joint action coordination between the age of 2½ and 3, but both age groups performed equally well when acting individually. Interestingly, 3-year-olds performed equally well in the joint and the individual condition, whereas 2½-year-olds did not yet show this adult-like pattern as indicated by less accurate performance in the joint action. The findings suggest that in contrast to 3-year-olds, 2½-year-olds still have difficulties in establishing well-coordinated joint action with an adult partner. Possible underlying cognitive abilities such as action planning and action control are discussed.
Joint actions are a part of everyday life. The success of a joint action is highly dependent on the ability to coordinate our own actions with those of our action partner (Sebanz et al.,
Action coordination entails the coordination between two people as well as intrapersonal action coordination. Though a large body of research is concerned with action and action coordination development, to date, investigations have often focused on intrapersonal coordination of actions (e.g., Clark et al.,
Also, the frequency of coordinated acts among peers was found to increase substantially between 16 and 32 months of age (Eckerman et al.,
One recent study investigated the continuous coordination of actions between young children and an adult during social interaction by examining 2½- to 4½-year-olds’ drumming behavior in social compared to non-social settings (Kirschner and Tomasello,
To investigate the development of joint and individual action coordination abilities, we tested 2½- and 3-year-old children by means of a sequential button-pressing game. The game could be played jointly with another person as well as individually. When playing jointly, the children were acting together with an adult experimenter. To keep the adult's behavior constant between children and avoid scaffolding, the adult's action timing was locked to the children's responses. By always acting 1 s after the child, the action partner played in a predictable manner which at the same time was dependent on the child and thus interactive in nature. In line with Deutsch and Newell (
Twenty-three young children were included in the final sample. They were recruited from a database of families who volunteered to participate in child studies. The total sample consisted of two age groups: ten 2½-year-olds (mean age = 30 months and 3 days, range = 29 months and 22 days to 30 months and 11 days; 7 girls) and thirteen 3-year-olds (mean age = 36 months and 1 day, range = 35 months and 22 days to 36 months and 9 days; 7 girls). All children were accompanied to the testing session by a parent who gave written consent for the restricted use of video recordings obtained during the experiment. Another 18 participants were tested but excluded from the analysis due to incomplete task demonstration caused by interference of the child (
A 2 × 2 mixed design with one between-subjects factor (age group) and one within-subjects factor (condition) was used in the current study. Each child played the button-pressing game together with the experimenter (joint condition) and alone (individual condition). The order of conditions within a session was counterbalanced across participants such that five out of ten 2½-year-old children as well as six out of thirteen 3-year-olds started with the individual condition. All data were collected by the same first experimenter (E1) who was the joint action partner of the children.
We designed a simple computer game playable by repeatedly pressing two buttons in alternation. The two buttons were positioned in front of a computer screen (see Figure
To make the buttons more distinct they were colored differently (left button: black; right button: red). Button presses triggered the presentation of visual and auditory stimuli programmed in Python (Version 2.5, Python Software Foundation;
In addition to the registration of button presses, video recordings were made throughout the experiment. A digital video camera (Sony Handycam, DCR-SR190E) was placed in the corner of the room to record children's behavior during the testing sessions.
The experiment was conducted in a quiet testing room. Before child and parent were introduced to the testing room, they were invited to spend a short period (<10 min) in an adjacent playroom. During this warming-up period parents were informed about the general course of the experimental session, while the child had the opportunity to get accustomed to the two experimenters E1 and E2. E1 was the active joint action partner of the children while E2 helped to demonstrate the joint condition. The warming-up phase was included to facilitate children's engagement in social contact with E1 during the actual testing phase.
After the short warming-up period child and parent were accompanied by E1 and E2 to the testing room. There, the parent was instructed to sit down at a table on which the set-up was installed. The caregiver was asked to sit with the child on his or her lap such that the child could comfortably reach the buttons. E1 then took a seat to the left of child and parent while E2 remained in the background. Parents were asked not to interfere throughout the testing phase. To introduce the general idea of the game, E1 pointed to the moving character on the screen (the frog), to the ladder and to the goal location (the piglet on the cloud). She explained that the frog wanted to climb up the ladder to reach the piglet on the cloud. After this general introduction, each child was asked to engage in two consecutive conditions, an individual, and a joint condition. Both conditions were preceded by a demonstration trial.
The child's task in the individual condition was to move the frog from the bottom of the screen to the goal position at the top by pushing the two buttons in turn using the left hand for the left button and the right hand for the right button. E1 demonstrated this task by completing one trial on her own. Moreover, a verbal instruction of the task was given. After demonstration, the frog was reset to its starting position and children were invited to play on their own. The experimenter encouraged the children to play individually for several, but maximally four times. The number of trials completed varied between children, but other than one child all participants engaged in the individual condition.
In the joint condition, children were instructed to play together with E1. The sequence of button presses (i.e., left, right, left etc.) required to accomplish the goal of the game was the same as in the individual condition. However, in the joint condition, the child was asked to use only the right button with the right hand whereas E1 had control over the left button such that the child and E1 had to take turns pushing the buttons to succeed in the task. As in the individual condition, a demonstration trial preceded the actual test trials. For this purpose, E2 joined and sat down left of E1 in a position visible for the child. In the demonstration trial E1 and E2 carried out the task together by taking turns to push the buttons until they reached the goal jointly. Consistent with the individual condition a verbal explanation of the task was given during the demonstration. After one demonstration trial, E2 left the table again and the game was reset to the start. Then, the test trial was started by inviting the child to play together with E1. Again, children were allowed to play several times up to a maximum of four trials. Except for two participants, all children participated in the joint condition. Throughout the joint play E1 heard via an earphone a metronome tone which was locked to the child's response. The metronome tone consisted of three consecutive beep tones with the last beep presented exactly 1 s after the right (i.e., the child's) button had been pressed. This button-locked metronome feedback was only audible for E1. It allowed E1 to respond to the child's button presses in a consistent and predictable manner by pressing her own button approximately 1 s after the child's response.
We focused on two measures to test our hypotheses:
Before calculating these two measures the data were preprocessed in the following way: the first two button presses of each trial were excluded from the data analysis to prevent a bias of large outliers at the beginning of a trial (cf. Drewing et al.,
To perform the sequential button pressing task accurately, the two buttons had to be pushed in turn. Therefore, a button press executed more than once in a row was counted as error. To compare children's performance accuracy between conditions the mean percentage of these errors was assessed.
Besides children's accuracy we investigated how stable children were in their response timing. With regard to performance in voluntary movement tasks, a decrease in variability with increasing age has been associated with improvement in performance (Piek,
Though E1 was provided with metronome tones to achieve a standardized performance, children's behavior such as the production of errors might have introduced additional variability to E1’s performance. To ensure that no systematic differences in the performance of E1 occurred between age groups, we tested the mean time interval, (i.e., the average time it took E1 to push the button after the child's response) and E1’s timing variability, against age groups. Neither the mean time interval,
Preliminary tests for order effects were conducted by including the order of conditions (individual first; joint first) as a within-participants factor in each mixed analysis of variance (ANOVA). Since the order of conditions never yielded significant differences (all
Figure
Children's average time interval between button presses served as the basis for the subsequent measure of variability in response timing. Comparing the average interval timing across age groups and conditions by means of a mixed ANOVA revealed a main effect of both, Age Group,
The average COV for the two age groups and conditions are depicted in Figure
In this study, we investigated the development of young children's action coordination in a repetitive button-pressing task. We compared 2½- and 3-year-olds’ performance when acting either together with a joint action partner or individually. Three-year-old children showed higher accuracy in their coordination with an adult partner than 2½-year-olds. However, when acting on their own, the 2½-year-olds were as accurate in their bimanual coordination as the 3-year-old children. The same pattern was found for the variability in children's interval timing. While the 3-year-olds showed less variability in the joint condition than the 2½-year-olds, there was no difference in variability between age groups in the individual condition. These findings indicate that the ability to coordinate one's own actions with those of another person improves significantly between the age of 2½ and 3 years. In contrast to joint action coordination, no developmental changes between 2½- and 3-year-old children were found regarding intrapersonal action coordination.
Both accuracy and stability of performance are important indicators of the quality of action coordination between two people. With respect to accuracy, 2½-year-old children impeded the joint action coordination by acting significantly more often when it was not their turn. Two potential explanations could account for this higher percentage of errors in the joint condition as observed in the 2½-year-olds. Deficits in action control as well as action planning might play a role in adjusting actions properly. On the action control level, one possible reason might be the lack of response inhibition (Diamond,
On the other hand, the children's behavior might reflect difficulties on the action planning level, namely in incorporating the other person's actions into their own action plan. Incorporating the other into one's action plan requires the understanding of the other's contribution to and importance for the common action. The 2½-year-olds might have acted more frequently when it was the other's turn because they did not yet fully integrate the adult as an essential part of the joint action. Adults have been shown to incorporate other people's actions by sharing representations of others’ actions and tasks, a skill which is thought to be crucial for understanding and predicting other's actions in a social interaction (Sebanz et al.,
In addition to the higher error rate, the variable temporal performance of 2½-year-olds also indicates less proficient joint action coordination. Though not mandatory for the successful execution of the game, acting in a stable temporal manner facilitates the action coordination between the two actors. While keeping a stable response timing can help to establish a smooth joint coordination, a high variability in response timing might impede smooth joint coordination. What might have caused the more variable performance of the younger children? While the children were active throughout the individual condition by pushing either with their left or right hand they had to refrain from acting in the joint condition during their partner's turn. With respect to action control, activating one's actions after refraining from acting might have been less automatic in the younger children than in older children. This might have led to the higher variability in their action timing. Whether this effect is specific to joint action situations or whether young children have the same difficulties in a non-social context remains to be clarified.
On the action planning level, difficulties in incorporating the other person's actions into one's own action plan might account for the more variable action timing of the 2½-year-olds. As 2½-year-olds did not reliably adapt their own action timing to the other's actions, the results might suggest that the degree to which they incorporate the partner as an essential part of the common action is more limited compared to the 3-year-olds.
Interestingly, the integration of other information inherent to joint actions such as obligations and commitments toward the action partner has also been observed to emerge around the same age (Gräfenhain et al.,
With regard to the coordination of individual actions, we expected only marginal changes between age groups. In accordance with this hypothesis, no significant differences in accuracy and variability were found between the age groups in the individual condition. Previous developmental research on intrapersonal coordination found various stable bimanual movement patterns such as in- and anti-phase movements as early as 24 months of age (Brakke et al.,
Since developmental changes in action coordination were specifically found for joint action coordination but not individual action coordination we would assume that planning processes crucial for successful joint actions rather than mere action control abilities contribute substantially to this development. The ability to integrate information about one's own and another's actions is emphasized as being important for acting jointly (Sebanz et al.,
Although we did not have any specific predictions concerning the average interval time, children were shown to be overall slower in the joint than in the individual condition. One explanation for this finding might be an adjustment to their partner's action timing (cf. Kirschner and Tomasello,
In general, children in the current experiment were acting with an adult action partner, who was acting in a predictable and reliable manner. Therefore, conclusions with respect to children's flexibility in joint actions as required when interacting with a same-aged peer or a less reliable adult are limited. It would be interesting to vary this aspect in a subsequent experiment to determine how young children adjust to more variable action partners in situations that resemble daily life. Previous research investigating interaction between peers indicates that young children are more challenged when acting jointly with a child of the same age than they would be with an adult partner (cf. Hunnius et al.,
Action coordination lately gained interest as a crucial factor for joint action development (see Brownell et al.,
However, the action type and task requirements of the current study might differ from the coordination demands of the tasks used previously (e.g., Warneken et al.,
Strikingly, by the age of 3, children reached a degree of proficiency in joint action coordination which was as high as their individual coordination performance. Thus, the current results indicate that children's joint action coordination skills improve considerably in the last half of their third year of life and approach adult-like relations between joint action coordination and intrapersonal coordination. Taken together, although children already seem to be able to accomplish a task together with another person at the end of their second year of life (e.g., Brownell and Carriger,
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We thank the parents and children who participated in our study. We also wish to thank Pascal de Water, Gerard van Oijen, and Norbert Hermesdorf for their technical support and Florian Krause for programming the computer game. We would like to acknowledge the contributions of our lab managers Angela Khadar and Margret van Beuningen and thank our research assistant Evelien Akker for her help with testing. This work was supported by a VICI Grant to the second author (453-05-001) from the Dutch Organization for Scientific Research (NWO).