This research was supported by Promotion of Doctoral Studies (PODS) I and II awards from the Foundation for Physical Therapy and an Adopt-A-Doc Scholarship from the Education Section of the American Physical Therapy Association to Barbara Sargent.

The Institutional Review Board at the University of Southern California approved this study.
1.&#160;System Preparation
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	<li>Set up the motion capture system. Please note: these steps are different for each motion capture system.
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		<li>Align the coordinate systems of the two motion capture sensors to that of one sensor by clicking &#8220;Perform New Registration&#8221; in the motion capture program, entering a collection time of 30 sec, clicking &#8220;Register,&...

<ol>
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P., Kubo, M., Tronick, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spontaneous+kicking+in+full-term+and+preterm+infants+with+and+without+white+matter+disorder.">Spontaneous kicking in full-term and preterm infants with and without white matter disorder.</a> Dev. Psychobiol. 52 (6), 524-536 (2010).</li><li>Emmerick, R., Wagenaar, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+walking+velocity+on+relative+phase+dynamics+in+the+trunk+in+human+walking.">Effects of walking velocity on relative phase dynamics in the trunk in human walking.</a> J. Biomech. 29 (9), 1175-1184 (1996).</li><li>Kelso, J. A., Scholz, J. P., Schoner, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonequilibrium+phase+transitions+in+coordinated+biological+motion:+critical+fluctuations.">Nonequilibrium phase transitions in coordinated biological motion: critical fluctuations.</a> Physics Letters A. 134 (6), 8-12 (1986).</li><li>Schneider, K., Zernicke, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass,+center+of+mass,+and+moment+of+inertia+estimates+for+infant+limb+segments.">Mass, center of mass, and moment of inertia estimates for infant limb segments.</a> J. Biomech. 25 (2), 145-148 (1992).</li><li>Sun, H., Jensen, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Body+segment+growth+during+infancy.">Body segment growth during infancy.</a> J. Biomech. 27 (3), 265-275 (1994).</li><li>Murray, R. M., Li, Z., Sastry, S. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> A Mathematical Introduction to Robotic Manipulation. , (1994).</li><li>Galloway, J. C., Koshland, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=General+coordination+of+shoulder,+elbow+and+wrist+dynamics+during+multijoint+arm+movements.">General coordination of shoulder, elbow and wrist dynamics during multijoint arm movements.</a> Exp. 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Sci. 22, 729-748 (2004).</li><li>Jeng, S., Chen, L., Yau, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinematic+analysis+of+kicking+movements+in+preterm+infants+with+very+low+birth+weight+and+full-term+infants.">Kinematic analysis of kicking movements in preterm infants with very low birth weight and full-term infants.</a> Phys. Ther. 82, 148-159 (2002).</li><li>Jensen, J. L., Thelen, E., Ulrich, B. D., Schneider, K., Zernicke, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adaptive+dynamics+of+the+leg+movement+patterns+of+human+infants:+III.+age-related+differences+in+limb+control.">Adaptive dynamics of the leg movement patterns of human infants: III. age-related differences in limb control.</a> J. Mot. Behav. 27, 366-374 (1995).</li><li>Piek, J. 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Design of discovery-learning tasks for young infants
Discovery-learning tasks for young infants must be thoughtfully designed to assure that infants are independently discovering the contingency. In several mobile paradigms at the beginning of the acquisition condition, infants are either shown that the mobile activates by a non-contingent activation of the mobile7,22 or the leg of each infant is passively moved by the investigator to introduce the infant to the contingency9</s...

Task-specific actions emerge from spontaneous movements during infancy. It has been proposed that task-specific actions emerge through a discovery-learning process1,2. Tasks are discovered by infants as they spontaneously move and explore actions which produce novel effects in the environment. Task-specific actions emerge as infants exploit the connections between their actions and their effects on the world around them. However, little is known about the precise processes that infants explore and exploit to learn to modify their spontaneous movements to perform task-specific actions. Here a method is described in which 3-4 month old infants learn a task by discovery and their leg movements are captured to quantify the learning process.
<img alt="Figure 1" src="/files/ftp_upload/52841/52841fig1.jpg" />
Figure 1: Infant kicking-activated mobile task. The center light-emitting diode (LED) attached to the rigid body of each foot (yellow circle) activates the mobile when it crosses the virtual threshold (red dashed line). Re-printed with permission from Sargent et al.3
This discovery-learning task uses an infant activated mobile that rotates and plays music based on the specified leg action of infants3. Infants placed supine under the mobile activate it by moving their feet vertically across a virtual threshold (Figure 1). This paradigm is unique in that as infants independently discover that their leg actions activate the mobile, the infants&#8217; leg movements are tracked using a motion capture system allowing for the quantification of the learning process.
The experimental protocol includes two days of data collection. Day 1 consists of a 2 min baseline condition in which an infant kicks spontaneously but his leg actions cannot activate the infant mobile, followed by a 6 min acquisition condition in which the infant&#8217;s leg actions activate the infant mobile if the infant moves his feet vertically to cross a virtual threshold. This protocol allows for the quantification of infants&#8217; spontaneous leg actions as well as the quantification of various aspects of the movements as infants explore the relation between their leg actions and activation of the infant mobile. On Day 2, in addition to the 2 min baseline condition and 6 min acquisition condition, a 2 min extinction condition is added in which the infant&#8217;s leg actions do not activate the infant mobile. This allows for the quantification of how infants change their leg actions when an already learned environmental response is discontinued.
In previous infant mobile paradigms, frequency of leg movement4-6, specific hip and knee angles7,8, or kicking a panel9 have been reinforced with mobile movement. Performance each day was defined as an increase in these leg actions during the acquisition or extinction condition as compared to the baseline condition4-9. Learning across days was defined as an increase in these leg actions during the baseline or acquisition condition of Days 2 or 3 and the baseline condition of Day 15,6. These previous mobile paradigms demonstrate that infants increase the frequency of leg actions that are reinforced with mobile activation, however, they do not provide information on the movement options infants have available to them when learning the task. For example, if kicking rate is reinforced, infants demonstrate performance and learning when their kicking rate increases either when interacting with the mobile or when the mobile no longer activates. This demonstrates that infants can refine their kicking rate, but it is unknown if infants can refine their leg coordination pattern or torque production to generate leg actions that are not within their preferred movement repertoire.
This mobile paradigm is unique in that infants are required to demonstrate more refined&#160;leg action to activate the mobile than in previous mobile paradigms. In this mobile paradigm, the height of each foot above the table is computed during the 2 min baseline condition using position data from a light emitting diode (LED) attached to each foot. A virtual threshold is then set parallel to the table at a height that is within the upper range of the height of both feet during the baseline condition. During acquisition, the mobile rotates and plays music if either foot crosses the threshold. After 3 sec, the mobile stops and reactivates only if the infant moves the foot below the threshold, and then moves the foot vertically and again crosses the threshold. To activate the mobile for the greatest amount of time, infants need to move a foot above the threshold and maintain it against gravity for 3 sec, then quickly move the foot below the threshold and again move it above the threshold and hold it there for 3 sec, etc. This requires more refined leg action&#160;than simply increasing kicking rate.
<img alt="Figure 2" src="/files/ftp_upload/52841/52841fig2.jpg" />
Figure 2: Unfiltered position data of end effectors (feet) from a representative infant. Unfiltered position data from Day 2 of a 3 month old infant who demonstrated learning based on the individual learning criteria. The red line is position data of the z-coordinate of the light-emitting diode (LED) placed on the right foot. The blue line is position data from the LED on the left foot. Thick black line is the table. Dotted line is the virtual threshold placed 14 cm above the table as individually determined for each infant based on the height of their kicking during baseline condition of Day 1. X-axis is time labeled by 2 min intervals. Note how the infant moves his feet during baseline when the mobile does not activate and during the first 30 sec of acquisition 1, then he consistently keeps both feet off the table and moves his feet right around the threshold for the next 5&#189; min until the mobile no longer activates during the extinction condition.
The second unique feature of this mobile paradigm is that each infant&#8217;s leg action is tracked using state-of-the-art motion capture techniques to quantify how infants use their movement options&#160;to learn the task. Unfiltered position data of the LED on each foot that activates the mobile from one representative infant is included in Figure 2. Note how the infant moves his feet at various heights above the table during baseline and the first part of acquisition, but then moves both feet right around the threshold during the rest of the acquisition condition until the mobile no longer activates during extinction. This is one of many potential movement strategies to accomplish the discovery-learning task. The strategies can be quantified by computing three-dimensional kinematics and kinetics using position data acquired from the motion capture system. Specifically, the learning process is quantified in terms of the percentage of reinforced leg action (%RLA), which is equal to the duration of mobile activation, position variance of the end effectors (feet) which activate the mobile, hip-knee coordination patterns, and hip and knee joint torques.

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quantifying learning in young infants: tracking leg actions during a discovery-learning task

Task-specific actions emerge from spontaneous movement during infancy. It has been proposed that task-specific actions emerge through a discovery-learning process. Here a method is described in which 3-4 month old infants learn a task by discovery and their leg movements are captured to quantify the learning process. This discovery-learning task uses an infant activated mobile that rotates and plays music based on specified leg action of infants. Supine infants activate the mobile by moving their feet vertically across a virtual threshold. This paradigm is unique in that as infants independently discover that their leg actions activate the mobile, the infants&#8217; leg movements are tracked using a motion capture system allowing for the quantification of the learning process. Specifically, learning is quantified in terms of the duration of mobile activation, the position variance of the end effectors (feet) that activate the mobile, changes in hip-knee coordination patterns, and changes in hip and knee muscle torque. This information describes infant exploration and exploitation at the interplay of person and environmental constraints that support task-specific action. Subsequent research using this method can investigate how specific impairments of different populations of infants at risk for movement disorders influence the discovery-learning process for task-specific action.

The learning process of young infants can be quantified in terms of the %RLA, position variance of the end effectors (feet), hip-knee angle correlation coefficients, and hip and knee joint torques. Each level of analysis provides unique information about how infants explore the relation between their leg actions and activation of the infant mobile during the discovery-learning process.
For the statistical analysis of %RLA and hip-knee angle correlation coefficients, mixed regression models wit...

Watch this Scientific Journal Video about Quantifying Learning in Young Infants: Tracking Leg Actions During a Discovery-learning Task at JoVE.com

Quantifying Learning in Young Infants: Tracking Leg Actions During a Discovery-learning Task

A method is described in which 3-4 month old infants learn a task by discovery and their leg movements are captured to quantify the learning process.

Task-specific actions emerge from spontaneous movement during infancy. It has been proposed that task-specific actions emerge through a discovery-learning ...

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10.5K visualizações.  University of Southern California. A method is described in which 3-4 month old infants learn a task by discovery and their leg movements are captured to quantify the learning process.