Head-mounted eye tracking: a new method to describe infant looking

Abstract

Despite hundreds of studies describing infants' visual exploration of experimental stimuli, researchers know little about where infants look during everyday interactions. The current study describes the first method for studying visual behavior during natural interactions in mobile infants. Six 14-month-old infants wore a head-mounted eye-tracker that recorded gaze during free play with mothers. Results revealed that infants' visual exploration is opportunistic and depends on the availability of information and the constraints of infants' own bodies. Looks to mothers' faces were rare following infant-directed utterances but more likely if mothers were sitting at infants' eye level. Gaze toward the destination of infants' hand movements was common during manual actions and crawling, but looks toward obstacles during leg movements were less frequent.

Figure 1

(A) Infant wearing head-mounted eye-tracker, wireless transmitter, and battery pack. (B) Gaze video exported with Yarbus software. Red crosshairs indicates the infant’s point of gaze. Inset shows picture-in-picture video from the eye camera.

Figure 2

Timeline of 15 s of one infant’s interactions with her mother. The top row shows the infant’s eye gaze—white bars are fixations of people (mother, experimenter), light gray bars are fixations of objects, and dark gray bars are fixations of obstacles. The second and third rows mark the infant’s manual interactions with two different objects. The fourth row shows each of the mother’s vocalizations. The fifth row displays the infant’s locomotor activity and the ground surface on which the infant is moving (floor or 23-cm pedestal).

Figure 3

Hypothetical timeline showing fixation initiation and termination relative to the moment of limb contact (vertical dashed line). (A) Fixation beginning and ending before limb contact. (B) Fixation continuing through the moment of limb contact, providing online visual information of the target.

Figure 4

Histograms showing the timing of fixations to objects and obstacles for reaching, walking, and crawling encounters. Vertical dashed lines indicate the moment of limb contact. Fixation initiation is shown in (A). Fixation termination is shown in (B).