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1. Age-dependent differences in learning to control a robot arm using a body-machine interface

   https://doi.org/10.1038/s41598-018-38092-3  

   Ranganathan, Rajiv ; Lee, Mei-Hua ; Padmanabhan, Malavika R. ; Aspelund, Sanders ; Kagerer, Florian A. ; Mukherjee, Ranjan ( February 2019 , Scientific Reports)

   Body-machine interfaces, i.e. interfaces that rely on body movements to control external assistive devices, have been proposed as a safe and robust means of achieving movement and mobility; however, how children learn these novel interfaces is poorly understood. Here we characterized the learning of a body-machine interface in young unimpaired adults, two groups of typically developing children (9-year and 12-year olds), and one child with congenital limb deficiency. Participants had to control the end-effector of a robot arm in 2D using movements of the shoulder and torso. Results showed a striking effect of age - children had much greater difficulty in learning the task compared to adults, with a majority of the 9-year old group unable to even complete the task. The 12-year olds also showed poorer task performance compared to adults (as measured by longer movement times and greater path lengths), which were associated with less effective search strategies. The child with congenital limb deficiency showed superior task performance compared to age-matched children, but had qualitatively distinct coordination strategies from the adults. Taken together, these results imply that children have difficulty learning non-intuitive interfaces and that the design of body-machine interfaces should account for these differences in pediatric populations.

    

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2. Children show limited movement repertoire when learning a novel motor skill

   Lee, Mei-Hua ; Farshchiansadegh, Ali ; Ranganathan, Rajiv ( September 2017 , Developmental science)

   Examining age differences in motor learning using real-world tasks is often problematic due to task novelty and biomechanical confounds. Here, we investigated how children and adults acquire a novel motor skill in a virtual environment. Participants of three different age groups (9-year-olds, 12-year-olds, and adults) learned to use their upper body movements to control a cursor on a computer screen. Results showed that 9-year-old and 12-year-old children showed poorer ability to control the cursor at the end of practice. Critically, when we investigated the movement coordination, we found that the lower task performance of children was associated with limited exploration of their movement repertoire. These results reveal the critical role of motor exploration in understanding developmental differences in motor learning. 

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3. Children show limited movement repertoire when learning a novel motor skill

   https://doi.org/10.1111/desc.12614  

   Lee, Mei‐Hua ; Farshchiansadegh, Ali ; Ranganathan, Rajiv ( September 2017 , Developmental Science)

   Examining age differences in motor learning using real‐world tasks is often problematic due to task novelty and biomechanical confounds. Here, we investigated how children and adults acquire a novel motor skill in a virtual environment. Participants of three different age groups (9‐year‐olds, 12‐year‐olds, and adults) learned to use their upper body movements to control a cursor on a computer screen. Results showed that 9‐year‐old and 12‐year‐old children showed poorer ability to control the cursor at the end of practice. Critically, when we investigated the movement coordination, we found that the lower task performance of children was associated with limited exploration of their movement repertoire. These results reveal the critical role of motor exploration in understanding developmental differences in motor learning.

    

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4. Moving a missing hand: children born with below elbow deficiency can enact hand grasp patterns with their residual muscles

   https://doi.org/10.1186/s12984-024-01306-z  

   Fitzgerald, Justin J. ; Battraw, Marcus A. ; James, Michelle A. ; Bagley, Anita M. ; Schofield, Jonathon S. ; Joiner, Wilsaan M. ( January 2024 , Journal of NeuroEngineering and Rehabilitation)

   Children with a unilateral congenital below elbow deficiency (UCBED) have one typical upper limb and one that lacks a hand, ending below the elbow at the proximal/mid forearm. UCBED is an isolated condition, and affected children otherwise develop normal sensorimotor control. Unlike adults with upper limb absence, the majority of whom have an acquired loss, children with UCBED never developed a hand, so their residual muscles have never actuated an intact limb. Their ability to purposefully modulate affected muscle activity is often assumed to be limited, and this assumption has influenced prosthetic design and prescription practices for this population as many modern devices derive control signals from affected muscle activity. To better understand the motor capabilities of the affected muscles, we used ultrasound imaging to study 6 children with UCBED. We examined the extent to which subjects activate their affected muscles when performing mirrored movements with their typical and missing hands. We demonstrate that all subjects could intentionally and consistently enact at least five distinct muscle patterns when attempting different missing hand movements (e.g., power grasp) and found similar performance across affected and typically developed limbs. These results suggest that although participants had never actuated the missing hand they could distinctively and consistently activate the residual muscle patterns associated with actions on the unaffected side. These findings indicate that motor control still develops in the absence of the normal effector, and can serve as a guide for developing prostheses that leverage the full extent of these children’s motor control capabilities.

    

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5. Developmental changes in the categorization of speech and song

   https://doi.org/10.1111/desc.13346  

   Vanden Bosch der Nederlanden, Christina M. ; Qi, Xin ; Sequeira, Sarah ; Seth, Prakhar ; Grahn, Jessica A. ; Joanisse, Marc F. ; Hannon, Erin E. ( November 2022 , Developmental Science)

   Music and language are two fundamental forms of human communication. Many studies examine the development of music‐ and language‐specific knowledge, but few studies compare how listeners know they are listening to music or language. Although we readily differentiate these domains, how we distinguish music and language—and especially speech and song— is not obvious. In two studies, we asked how listeners categorize speech and song. Study 1 used online survey data to illustrate that 4‐ to 17‐year‐olds and adults have verbalizable distinctions for speech and song. At all ages, listeners described speech and song differences based on acoustic features, but compared with older children, 4‐ to 7‐year‐olds more often used volume to describe differences, suggesting that they are still learning to identify the features most useful for differentiating speech from song. Study 2 used a perceptual categorization task to demonstrate that 4–8‐year‐olds and adults readily categorize speech and song, but this ability improves with age especially for identifying song. Despite generally rating song as more speech‐like, 4‐ and 6‐year‐olds rated ambiguous speech–song stimuli as more song‐like than 8‐year‐olds and adults. Four acoustic features predicted song ratings: F0 instability, utterance duration, harmonicity, and spectral flux. However, 4‐ and 6‐year‐olds’ song ratings were better predicted by F0 instability than by harmonicity and utterance duration. These studies characterize how children develop conceptual and perceptual understandings of speech and song and suggest that children under age 8 are still learning what features are important for categorizing utterances as speech or song.

   Children and adults conceptually and perceptually categorize speech and song from age 4.

   Listeners use F0 instability, harmonicity, spectral flux, and utterance duration to determine whether vocal stimuli sound like song.

   Acoustic cue weighting changes with age, becoming adult‐like at age 8 for perceptual categorization and at age 12 for conceptual differentiation.

   Young children are still learning to categorize speech and song, which leaves open the possibility that music‐ and language‐specific skills are not so domain‐specific.

    

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