3-4-year-old children's memory flexibility allows adaptation to an altered context.

Imitation provides a reliable method to investigate the developing memory functions in childhood. The present study explored whether 3-4-year-old children are able to revise their previous experiences after a 1 week delay in order to adapt to an altered context. We used a combined short-term (Session 1) and delayed (Session 2) imitation paradigm based on a previous study with 2-year-olds. The constraints (target object close/far) and relatedly the relevance of using a tool in a goal attainment task (irrelevant/relevant, respectively) changed between the sessions. We found that children in Session 1 used the tool only when it was needed (relevant/object far context). After the 1 week delay when the tool was previously irrelevant and then became relevant, children remembered the irrelevant act and applied it in the altered context. When the tool lost its relevance after 1 week, children used the tool less than before, but did not fully omit it, despite its reduced efficiency. The present data with 3-year-olds was compared to a pattern of results with 2-year-olds (from a similar previous study), that allowed to discuss possible developmental transitions in memory and imitation. We propose that the flexible restoration of a formerly irrelevant act and the maintenance of a formerly successful solution indicate flexibility of preschooler's memory when guiding imitation. This flexibility, however, interacts with children's tendency to remain faithful to strategies that were previously ostensively demonstrated to them.

Human activity recognition of children with wearable devices using LightGBM machine learning.

Human activity recognition (HAR) using machine learning (ML) methods has been a continuously developed method for collecting and analyzing large amounts of human behavioral data using special wearable sensors in the past decade. Our main goal was to find a reliable method that could automatically detect various playful and daily routine activities in children. We defined 40 activities for ML recognition, and we collected activity motion data by means of wearable smartwatches with a special SensKid software. We analyzed the data of 34 children (19 girls, 15 boys; age range: 6.59-8.38; median age = 7.47). All children were typically developing first graders from three elementary schools. The activity recognition was a binary classification task which was evaluated with a Light Gradient Boosted Machine (LGBM) learning algorithm, a decision tree based method with a threefold cross validation. We used the sliding window technique during the signal processing, and we aimed at finding the best window size for the analysis of each behavior element to achieve the most effective settings. Seventeen activities out of 40 were successfully recognized with AUC values above 0.8. The window size had no significant effect. In summary, the LGBM is a very promising solution for HAR. In line with previous findings, our results provide a firm basis for a more precise and effective recognition system that can make human behavioral analysis faster and more objective.

The flexibility of early memories: Limited reevaluation of action steps in 2-year-old infants.

This study investigated the flexibility of 2-year-old infants' retrieval and reenactment processes. In a delayed imitation paradigm, children were exposed to a constraint change (implemented by the distance of a target object) affecting the relevance of using a tool to obtain a goal (reach the object). In Experiment 1, during demonstration in the first session the tool was either relevant or irrelevant for reaching the goal, and 1 week later it either lost or gained its relevance, respectively. We found that when the tool became unnecessary (relevant to irrelevant change), children used it somewhat less than before and used it less compared with when the tool's relevance remained the same (relevant to relevant, no change). When the tool became necessary after a constraint change (irrelevant to relevant change), children used the tool more than before, but not as much as in the Relevant-Relevant control condition. In Experiment 2, the timing of the constraint change (immediate or delayed) was varied in a modified version of the Irrelevant-Relevant condition, where practice before the constraint change was omitted. Children were not significantly more flexible in the immediate condition than in the delayed condition, and comparisons with Experiment 1 showed that performance did not change if we omitted the practice before the change. These results indicate that although 2-year-olds show considerable mnemonic performance, they face difficulties in adapting to constraint changes. We propose that this inflexibility may stem from infants' inability to revise their evaluations formed in previous events due to their immature episodic memory capacities.