A View of Their Own: Capturing the Egocentric View of Infants and Toddlers with Head-Mounted Cameras

Summary

Infants and toddlers view the world in a fundamentally different way from their parents. Head-mounted cameras provide a tractable mechanism to understand the infant visual environment. This protocol provides guiding principles for experiments in the home or laboratory to capture the egocentric view of toddlers and infants.

Abstract

Infants and toddlers view the world, at a basic sensory level, in a fundamentally different way from their parents. This is largely due to biological constraints: infants possess different body proportions than their parents and the ability to control their own head movements is less developed. Such constraints limit the visual input available. This protocol aims to provide guiding principles for researchers using head-mounted cameras to understand the changing visual input experienced by the developing infant. Successful use of this protocol will allow researchers to design and execute studies of the developing child's visual environment set in the home or laboratory. From this method, researchers can compile an aggregate view of all the possible items in a child's field of view. This method does not directly measure exactly what the child is looking at. By combining this approach with machine learning, computer vision algorithms, and hand-coding, researchers can produce a high-density dataset to illustrate the changing visual ecology of the developing infant.

Introduction

For decades, psychologists have sought to understand the environment of the developing infant, which William James famously described as a "blooming, buzzing confusion¹." The everyday experiences of the infant are typically studied by filming naturalistic play with social partners from a third-person perspective. These views from the side or above typically show cluttered environments and a daunting number of potential referents for any new word an infant hears². To an outside observer, James's description is apt, but this stationary, third-person perspective is not the way an infant sees the world. An infant is closer to the ground and can move through their world, bringing objects closer for visual exploration. A third-person view of a parent-infant interaction is illustrated in Figure 1. Highlighted are the fundamental differences between their perspectives. Perhaps, the input that infants receive is not nearly as chaotic as anticipated by parents and researchers. The goal of methods with head-mounted cameras is to capture the infant experience from a first-person view in order to understand the visual environment available to them throughout development.

Head-mounted cameras, worn on a hat or headband, provide a window into the moment-to-moment visual experiences of the developing infant. From this perspective, the study of the structure and regularities in the infant's environment becomes apparent. Head-mounted cameras have revealed infants' visual experiences to be largely dominated by hands, both their own and their social partner's, and that face-looks, once considered imperative for establishing joint attention, are much scarcer than anticipated³. Head-mounted cameras have also shown that infants and their caregivers create moments when objects are visually dominant and centered in the infant's field of view (FOV), reducing the uncertainty inherent to object-label mapping⁴.

Head-mounted cameras capture the infants' first-person view based on head movements. This view is not perfectly synchronous with, or representative of, infant eye movements, which can only be captured in conjunction with an eye-tracker. For instance, a shift of only the eyes while keeping the head stationary, or a shift of the head while keeping the eyes fixed on an object, will create a misalignment between the infants' actual FOV and the one captured by the head camera. Nonetheless, during toy play, infants typically center the objects they are attending to, aligning their head, eyes, and the location of the toy with their body's midline⁵. Misalignments are rare and are typically created by momentary delays between an eye shift and the accompanying head turn³. Therefore, head-cameras are not well suited to capturing the rapid dynamics of shifts in attention. The strength of head-mounted cameras lies in capturing the everyday visual environment, revealing the visual content available to infants.

The following protocol and representative results will demonstrate how head-mounted cameras can be used to study the visual environment of infants and toddlers.

Protocol

The following procedure to collect data on infant and toddler’s visual experiences in the laboratory and at home was approved by the Indiana University Institutional Review Board. Informed consent was obtained from the infant’s caregiver.

1. Choose a Head Camera

NOTE: There are numerous small, lightweight, and portable cameras readily available for purchase (Figure 2).

1. Choose a head camera that is unobtrusive and will not influence the scenes being recorded.
   1. Mount the camera onto a snug hat or headband using a temporary adhesive or securely mount the camera onto a small plastic plate attached to the headband. Position the camera at the child’s brow (Figure 2B, left).
      1. Depending on the shape of the camera, mount the camera by sewing small cloth loops into a headband or hat (Figure 2B, center and right).
      2. Ensure that the hat or headband are adjustable to achieve a snug and comfortable fit on the child’s head (Figure 2A).
         NOTE: A camera located directly between the eyes of the infant is theoretically ideal, however this is not quite possible with current technology. Small cameras that can be placed low on the forehead are becoming increasingly available.
2. If cameras are being sent home with the parents, ensure that parents can use them without any technical help.
   1. Before the parents leave the laboratory, train them on how to operate the head camera.
   2. Send the parents home with the camera to use, the head-band or hat, and a hand-out describing the procedure to turn on the camera and record data.
3. Ensure that the cameras are light enough for infants to wear and forget about.
   NOTE: The recommended weight is less than 30 g³. Any chosen camera should not heat up during use and must be durable under heavy use.
4. If the experimental setup requires the children to be freely-moving, store recorded video to an internal storage card. Otherwise, use cameras tethered to the data collection computer.
5. Use a camera with a high-quality lens to better leverage recent advances in machine learning algorithms which segment visual scenes into regions of interest.
   1. If visual scenes will be manually coded by researchers, use a camera that can capture images at sufficient quality for manual inspection.
6. Ensure that any battery-powered camera is capable of recording for the desired amount of time.
7. Shortly before beginning the experiment or sending the camera home with the parents, test the head camera to ensure it is working appropriately.

2. Data Collection in the Laboratory

NOTE: Head-mounted cameras can be easily added to most experiments.

1. Have 2-3 experimenters place the camera onto the child’s head: one experimenter places the head camera, one monitors the head-camera view, and, if needed, one distracts the child.
   1. Ask the parent to ensure that the child remains calm and to distract the child during the placement process.
2. Perform the camera placement in three steps as follows.
   1. Desensitize the infant to hand actions near their head.
      1. Ask the parent to lightly touch or stroke the infant’s head and hair several times.
      2. Ask the experimenter placing the hat on the infant’s head to do the same as in 2.2.1.1.
   2. Have the experimenter place the head-mounted camera when the child is distracted.
      1. Use push-button toys to keep the child’s hands busy.
      2. Have the distracting experimenter or parent help at this stage by gently pushing the child’s hands toward the engaging toy so that the child’s hands do not go to the head.
   3. Tighten the hat on the child’s head and adjust the head camera when the child is engaged with the toy.
      1. Adjust the camera so that when the infant holds an object in front of his/her face, the object is centered in the head camera FOV.
      2. If the child is sitting, adjust the camera so that it captures most of the child’s lap when the child looks down.
3. After placing the camera on the child’s head, ask the experimenter to leave the room and begin the recording.
4. In the event that a camera is moved out of place or removed, re-enter the room to correct the camera.
   1. Terminate the experiment if the child does not tolerate the camera being reapplied.
      NOTE: For recording natural environments in the home, first fit a hat and camera to the individual infant and show parents how to position the camera. The design and fit of the camera must ensure that parents will be able to put the hat on their child without technical help.

3. Data Collection for the Parent-Infant Study

NOTE: The following representative method for head-cameras uses naturalistic toy play in the lab to demonstrate the type of analyses that can be conducted on the egocentric views of infants and their parents (Figure 3A).

1. Outfit the parent and child with head-mounted cameras, as described in 2.1 and 2.2.
2. Use head cameras to capture videos with a resolution of 720 x 1280 pixels at 30 frame/s. Proceed as described in steps 2.3 and 2.4.
   1. Subsample the video stream at one frame every 5 s.
   2. Manually draw bounding boxes around each toy (Figure 3B) within view using commercial software or a program developed in-house (see Figure 3C for a sample frame).
      1. If only part of a toy is visible due to occlusion by other toys or truncation on the edge of the frame, only draw bounding boxes when a toy is easily identifiable and include all visible parts of the toy.
      2. For example, if only the doll’s leg is visible, draw a bounding box around its leg. If an object occludes half of the doll, leaving the hair and legs visible, then draw a box that includes both hair and legs.

Results

One simple, yet informative, analysis is to count the number of objects in view at each point in time. Since a head camera produces data at approximately 30 Hz (30 images/s), down-sampling the data to 1 image every 5 s helps to produce a more manageable dataset while maintaining a resolution appropriate for understanding the types of scenes children see. Prior research has demonstrated that visual scenes are slow-changing in infants³. A custom script was used to dr...

Discussion

This paper outlines the basics for applying head-mounted cameras to infants to capture their egocentric visual scene. Commercially available head cameras are sufficient for the vast majority of studies. Small, lightweight, and portable cameras should be incorporated into a soft fabric hat or headband and applied to the child's head. Once successfully designed and implemented, a variety of experiments can be run, both in laboratory settings as well as in the home environment. From the videos gathered, aggregate data a...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Head-camera	Looxcie	Looxcie 3
Head-camera	Watec	WAT-230A
Head-camera	Supercircuits	PC207XP
Head-camera	KT&C	VSN500N
Head-camera	SereneLife	HD Clip-On
Head-camera	Conbrov	Pen TD88
Head-camera	Mvowizon	Smiley Face Spy Button
Head-camera	Narrative	Clip 2
Head-camera	MeCam	DM06