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

The goal of the following experiment is to investigate the emergence and development of leg movements when infants learn a specific task. This is accomplished by first placing an infant underneath an infant mobile and attaching camera visible markers to the infant's legs. Next, the infant's leg movements are tracked as she participates in a discovery learning task in which the mobile rotates and plays music.

Whenever the infant moves either foot vertically across a virtual threshold, the infant's leg movements are analyzed to determine if the infant learned that her leg action activated the mobile and how the infant changed her leg movements over the course of the experiment. Ultimately, this novel discovery learning paradigm provides information on the processes that infants explore and exploit when learning to modify their spontaneous movements to perform task specific actions. This paradigm is unique in that as infants independently discover that it is their leg action that activates the mobile.

Their leg movements are tracked using a motion capture system. Previous paradigms may have had one of these features, but both are necessary to quantify the learning process of young infants. This method can help us answer some of the key questions in the Field, such as how do infants learn by exploring the world around them.

To begin, set up the motion capture system by first aligning the coordinate system of the two motion capture sensors to that of a reference sensor. By first clicking on perform new registration in the motion capture program. Then enter a collection time of 30 seconds and click register.

Once register is clicked, move the registration object within the capture volume of the system for 30 seconds. When the registration is complete, a root means square registration will show up on the computer screen. Next click Perform New alignment in the motion capture program to align the global coordinate system to the testing table using the registration object, define the origin by placing the registration object on the upper right corner of the testing table and clicking digitize in the motion capture program.

Then define the Z axis by placing the registration object on top of a book and clicking, digitize the Z axis is perpendicular to the table. Next, define the ZY positive plane by moving the registration object on the book along the length of the table and clicking digitize. The Y axis is parallel to the length of the table, and the x axis is parallel to the width of the table.

Plug the LEDs into the two stroke ports and enter the number of LEDs per strobe port within the motion capture system program. Refer to figure three shown here. For the number and location of each LED, select the missing data view to provide a strip chart like display of LEDs being tracked in real time To set up the infant mobile program.

First, input the number of minutes for each condition for day one, input two. For phase one, the non reinforcement condition. Six for phase two, the reinforcement condition and zero for phase three on the second day, input two for phase one, six for phase two and two for phase three.

Also check the box. Use xin as default so that the threshold computed during baseline of day one will be the threshold used for the acquisition condition of day two. Finally, select stream frames, all frames and click send to enable the mobile program to use data from the motion capture system to activate the infant mobile based on specified criteria.

Next, position three cameras around the mobile setup, one at the right lateral, one at the left lateral, and one overhead. And connect them to the computer system. Initiate the video computer program to synchronize the three inputs.

Additionally, place a fourth camera over the infant's head to record facial expressions and to track eye gaze. Begin by describing the experiment to the parents and inform them to interact as little as possible with their infant. Next, undress the infant and place the infant under the mobile.

Secure the infant to the table using a Velcro band placed across the trunk. Once secured in place, attach the sternal markers followed by the foot, the shank, the thigh, and the pelvic rigid bodies of the infant. At the beginning of each testing day, initiate the mobile learning task by synchronously starting the motion capture system mobile computer program and video cameras observe the infant spontaneously kicking during the baseline period of the initial two minutes.

During this period, the infant mobile program will continuously compute the threshold for mobile activation based on the Z data from one of the LEDs on the rigid body of each foot at the end of the two minute baseline period. Observe as the mobile program sets the threshold at a height of one standard deviation above the average height of both feet during the baseline period. Next, during the acquisition condition, observe as the infant mobile rotates and plays music when the LED placed on either foot crosses the threshold that was computed during the two minute baseline condition from the first day of testing during the extinction phase.

On the second day of testing, observe as the infant kick spontaneously without any mobile reinforcement Following the infant interaction with the mobile fix. 10 individual LEDs bilaterally to the infant skin using double-sided EKG collars as shown here, hold the infant's lower extremity in an extended anatomical position for five seconds. Define the joint angles in this calibration position as zero degrees.

After the second day of testing, weigh the infant on a digital electric scale. Then measure the infant's length, their circumference at the mid segment of the thigh, the shank and the foot. Next, measure the width of their knee at the knee joint line.

The width of their ankle at the Malia line lie as well as the width of their foot at the metatarsal heads. Finally, measure the length of their thigh from the greater trocanter to the knee joint line the length of their shank from the knee joint line to the lateral malu and the length of their foot from the medial moly to the first metatarsal phlange joint. Analyze the infant's performance and learning by computing the percent of reinforced leg action as described in the accompanying text protocol.

To analyze leg movements, load position data files outputted from the motion capture system into a custom MATLAB program to interpolate missing position data for up to 20 consecutive frames using a cubic spline. Next, load the interpolated files into a custom MATLAB program to first filter the position data using a fourth order Butterworth with a cutoff frequency of five hertz, and then compute the joint angles as described by soderquist and wedin. This graph depicts differences in behavioral results between infants classified as learners, and those classified as non learners.

Infants were classified as learners if their reinforced leg action in the entire acquisition condition of day two was equal or greater than 1.5 times the reinforced leg action of their baseline condition on day one. Note the initial decrease in learners percent RLA during the first two minutes of the day one acquisition condition. Infants who learned the task decreased their overall action when the infant mobile began to activate, perhaps first as an orienting response, then perhaps as a strategy to determine whether their actions were associated with mobile activation.Shown.

Here are the differences in hip knee coordination between infants classified as learners and non learners. The learners, but not non learners, significantly decreased their hip knee angle correlation coefficient between the day two acquisition condition and the day one baseline condition. Here, the differences in hip and knee muscle torque impulse were analyzed in the group of infants classified as learners.

A robust finding was the increase in hip and knee muscle torque impulse during the extinction condition as compared to the other conditions. Infants who learned the task appear to be generating large hip and knee muscle torques during the extinction condition in an attempt to reactivate the mobile. This experimental paradigm can be extended to infants at risk for movement dysfunction.

It can be used to investigate how impairments of different populations of infants influence the discovery learning process and the ability to perform task specific leg action.