On the onset of eye-head coordination in infants

The world through infant eyes: Evidence for the early emergence of the cardinal orientation bias

The structure of the environment includes more horizontal and vertical (i.e. cardinal) orientations than oblique orientations, meaning that edges tend to be aligned with or perpendicular to the direction of gravity. This bias in the visual scene is associated with a bias in visual sensitivity in adults. Although infants must learn to function in this biased environment, their immature motor control prevents them from consistently orienting themselves, relative to gravity. This study therefore asked whether cardinal orientations dominate human visual experience from early infancy or only from later in development, as motor control improves. We analyze video clips from head-mounted cameras, showing the egocentric perspective of 75 infants (1 to 12 mo) in their home environments in two communities (Indiana, USA vs. Tamil Nadu, India). We measured the distribution of orientations in each frame of these videos and found that horizontal and vertical orientations were overrepresented in infants from both countries. A cardinal orientation bias was evident even in the egocentric view of the youngest infants (3 wk) and became more prominent during the subsequent weeks of development. The early presence of a cardinal orientation bias in infants' visual input may serve as a consistent cue to gravity and ground planes, potentially influencing motor development and contributing to the formation of sensory, perceptual, and cognitive biases.

An edge-simplicity bias in the visual input to young infants

The development of sparse edge coding in the mammalian visual cortex depends on early visual experience. In humans, there are multiple indicators that the statistics of early visual experiences has unique properties that may support these developments. However, there are no direct measures of the edge statistics of infant daily-life experience. Using head-mounted cameras to capture egocentric images of young infants and adults in the home, we found infant images to have distinct edge statistics relative to adults. For infants, scenes with sparse edge patterns-few edges and few orientations-dominate. The findings implicate biased early input at the scale of daily life that is likely specific to the early months after birth and provide insights into the quality, amount, and timing of the visual experiences during the foundational developmental period for human vision.

Head and eyes: Looking behavior in 12- to 24-month-old infants

This study demonstrates evidence for a foundational process underlying active vision in older infants during object play. Using head-mounted eye-tracking and motion capture, looks to an object are shown to be tightly linked to and synchronous with a stilled head, regardless of the duration of gaze, for infants 12 to 24 months of age. Despite being a developmental period of rapid and marked changes in motor abilities, the dynamic coordination of head stabilization and sustained gaze to a visual target is developmentally invariant during the examined age range. The findings indicate that looking with an aligned head and eyes is a fundamental property of human vision and highlights the importance of studying looking behavior in freely moving perceivers in everyday contexts, opening new questions about the role of body movement in both typical and atypical development of visual attention.

Double dissociation between perception and action in children

Previous research has demonstrated a functional dissociation between vision for perception and vision for action. However, the developmental trajectory of this functional dissociation is not well understood. We directly compared the sensitivity of grasping and perceptual estimations within the same experimental design to the real and illusory sizes of objects positioned in the Ponzo illusion display. Two different-sized objects were placed such that the differences between their real sizes and their perceived sizes were pitted against each other. Children aged 5-8 years and adults made perceptual size discriminations and then grasped (action) or estimated (perception) one of the objects based on its perceived size. Consistent with previous results, for the action task, grasping apertures of adults were scaled with the physical differences in the objects' sizes, even in trials where their overt perceptual decisions were deceived by the illusion. In contrast, perceptual estimations were robustly modulated by the illusion. Interestingly, children outperformed adults in their perceptual discriminations but exhibited adult-like behavior in grasping and in perceptual estimations of the objects, demonstrating a dissociation between perception and action. These results suggest that although the two visual functions are not operating at fully mature levels during childhood, some key mechanisms that support a dissociation between these functions are already in place.

Faces in early visual environments are persistent not just frequent

The regularities in very young infants' visual worlds likely have out-sized effects on the development of the visual system because they comprise the first-in experience that tunes, maintains, and specifies the neural substrate from low-level to higher-level representations and therefore constitute the starting point for all other visual learning. Recent evidence from studies using head cameras suggests that the frequency of faces available in early infant visual environments declines over the first year and a half of life. The primary question for the present paper concerns the temporal structure of face experiences: Is frequency the key exposure dimension distinguishing younger and older infants' face experiences, or is it the duration for which faces remain in view? Our corpus of head-camera images collected as infants went about their daily activities consisted of over a million individually coded frames sampled at 0.2 Hz from 232 h of infant-perspective scenes, recorded from 51 infants aged 1 month to 15 months. The major finding from this corpus is that very young infants (1-3 months) not only have more frequent face experiences but also more temporally persistent ones. The repetitions of the same very few face identities presenting up-close and frontal views are exaggerated in more persistent runs of the same face, and these persistent runs are more frequent for the youngest infants. The implications of early experiences consisting of extended repeated exposures of up-close frontal views for visual learning are discussed.

Real-world visual statistics and infants' first-learned object names

We offer a new solution to the unsolved problem of how infants break into word learning based on the visual statistics of everyday infant-perspective scenes. Images from head camera video captured by 8 1/2 to 10 1/2 month-old infants at 147 at-home mealtime events were analysed for the objects in view. The images were found to be highly cluttered with many different objects in view. However, the frequency distribution of object categories was extremely right skewed such that a very small set of objects was pervasively present-a fact that may substantially reduce the problem of referential ambiguity. The statistical structure of objects in these infant egocentric scenes differs markedly from that in the training sets used in computational models and in experiments on statistical word-referent learning. Therefore, the results also indicate a need to re-examine current explanations of how infants break into word learning.This article is part of the themed issue 'New frontiers for statistical learning in the cognitive sciences'.

Why are faces denser in the visual experiences of younger than older infants?

Recent evidence from studies using head cameras suggests that the frequency of faces directly in front of infants declines over the first year and a half of life, a result that has implications for the development of and evolutionary constraints on face processing. Two experiments tested 2 opposing hypotheses about this observed age-related decline in the frequency of faces in infant views. By the people-input hypothesis, there are more faces in view for younger infants because people are more often physically in front of younger than older infants. This hypothesis predicts that not just faces but views of other body parts will decline with age. By the face-input hypothesis, the decline is strictly about faces, not people or other body parts in general. Two experiments, 1 using a time-sampling method (84 infants, 3 to 24 months in age) and the other analyses of head camera images (36 infants, 1 to 24 months) provide strong support for the face-input hypothesis. The results suggest developmental constraints on the environment that ensure faces are prevalent early in development. (PsycINFO Database Record

Eye movement patterns and visual attention during scene viewing in 3- to 12-month-olds

Recently, two attentional modes have been associated with specific eye movement patterns during scene processing. Ambient mode, characterized by short fixations and long saccades during early scene inspection, is associated with localization of objects. Focal mode, characterized by longer fixations, is associated with more detailed object feature processing during later inspection phase. The aim of the present study was to investigate the development of these attentional modes. More specifically, we examined whether indications of ambient and focal attention modes are similar in infants and adults. Therefore, we measured eye movements in 3- to 12-months-old infants while exploring visual scenes. Our results show that both adults and 12-month-olds had shorter fixation durations within the first 1.5 s of scene viewing compared with later time phases (>2.5 s); indicating that there was a transition from ambient to focal processing during image inspection. In younger infants, fixation durations between two viewing phases did not differ. Our results suggest that at the end of the first year of life, infants have developed an adult-like scene viewing behavior. The evidence for the existence of distinct attentional processing mechanisms during early infancy furthermore underlines the importance of the concept of the two modes.

Contributions of head-mounted cameras to studying the visual environments of infants and young children

Head-mounted video cameras (with and without an eye camera to track gaze direction) are being increasingly used to study infants' and young children's visual environments and provide new and often unexpected insights about the visual world from a child's point of view. The challenge in using head cameras is principally conceptual and concerns the match between what these cameras measure and the research question. Head cameras record the scene in front of faces and thus answer questions about those head-centered scenes. In this "tools of the trade" article, we consider the unique contributions provided by head-centered video, the limitations and open questions that remain for head-camera methods, and the practical issues of placing head-cameras on infants and analyzing the generated video.

Computer vision tools for low-cost and noninvasive measurement of autism-related behaviors in infants

The early detection of developmental disorders is key to child outcome, allowing interventions to be initiated which promote development and improve prognosis. Research on autism spectrum disorder (ASD) suggests that behavioral signs can be observed late in the first year of life. Many of these studies involve extensive frame-by-frame video observation and analysis of a child's natural behavior. Although nonintrusive, these methods are extremely time-intensive and require a high level of observer training; thus, they are burdensome for clinical and large population research purposes. This work is a first milestone in a long-term project on non-invasive early observation of children in order to aid in risk detection and research of neurodevelopmental disorders. We focus on providing low-cost computer vision tools to measure and identify ASD behavioral signs based on components of the Autism Observation Scale for Infants (AOSI). In particular, we develop algorithms to measure responses to general ASD risk assessment tasks and activities outlined by the AOSI which assess visual attention by tracking facial features. We show results, including comparisons with expert and nonexpert clinicians, which demonstrate that the proposed computer vision tools can capture critical behavioral observations and potentially augment the clinician's behavioral observations obtained from real in-clinic assessments.

Eye tracking in early autism research

Eye tracking has the potential to characterize autism at a unique intermediate level, with links 'down' to underlying neurocognitive networks, as well as 'up' to everyday function and dysfunction. Because it is non-invasive and does not require advanced motor responses or language, eye tracking is particularly important for the study of young children and infants. In this article, we review eye tracking studies of young children with autism spectrum disorder (ASD) and children at risk for ASD. Reduced looking time at people and faces, as well as problems with disengagement of attention, appear to be among the earliest signs of ASD, emerging during the first year of life. In toddlers with ASD, altered looking patterns across facial parts such as the eyes and mouth have been found, together with limited orienting to biological motion. We provide a detailed discussion of these and other key findings and highlight methodological opportunities and challenges for eye tracking research of young children with ASD. We conclude that eye tracking can reveal important features of the complex picture of autism.

Visual tracking and its relationship to cortical development

Measurements of visual tracking in infants have been performed from 2 weeks of age. Although directed appropriately, the eye movements are saccadic at this age. Over the first 4 months of life, a rapid transition to successively smoother eye movements takes place. Timing develops first and at 7 weeks of age the smooth pursuit is well timed to a sinusoidal motion of 0.25 Hz. From this age, the gain of the smooth pursuit improves rapidly and from 4 months of age, smooth pursuit dominates visual tracking in combination with head movements. This development reflects massive cortical and cerebellar changes. The coordination between eyes-head-body and the external events to be tracked presumes predictive control. One common type of model for explaining the acquisition of such control focuses on the maturation of the cerebellar circuits. A problem with such models, however, is that although Purkinje cells and climbing fibers are present in the newborn, the parallel and mossy fibers, essential for predictive control, grow and mature at 4-7 months postnatally. Therefore, an alternative model that also includes the prefrontal cerebral cortex might better explain the early development of predictive control. The prefrontal cortex functions by 3-4 months of age and provides a site for prediction of eye movements as a part of cerebro-cerebellar nets.

Development of head movement propensity in 4–15 year old children in response to visual step stimuli

Head movement frequency of children in response to horizontal step stimulus is investigated. The aim is to determine if there is a correlation between the age of the child and the frequency of head movements made to visual step stimuli presented at a fixed distance. Also of importance is whether there is a period of rapid change in the frequency of head movements, and if so, what factors could be influencing this change. Seventy-three participants, between the ages of 4 and 15 years were requested to "look at a spot of light" in response to step stimuli which varied in size from 5 to 60 degrees. Eye and head movements were recorded with a video based eye tracker (EL-Mar 2020) equipped with a Flock of Birds head tracker. Frequency of head movements was calculated for each participant and averaged across participants for each age group. Average head movement frequency was then plotted as a function of age. The frequency and variability of head movements decreases as a function of age. This decrease is linear between the ages of 4 and 15 years (y = -1.465x + 22.58; R(2) = 0.4378; F = 26.48; P < 0.0001). More head movements are made in response to larger step sizes than to smaller ones for all ages. The gradual decrease in frequency of head movements in response to step stimuli suggests that a specific environmental event, such as reading, is not the cause of the decline. Improved efficiency of eye movements could be due to pre-programmed factors related to neurological development. Alternatively, cognitive factors may be involved. Children may actually learn that utilizing their head for gaze shifts is more energy and time consuming, than merely using the eyes alone.

The development of two-dimensional tracking: a longitudinal study of circular pursuit

We investigated 6- to 12-month-old infants' ability to track an object moving on circular trajectories, using a longitudinal design. Consistent predictive gaze tracking was not found before 8 months of age. These results indicate that infants' horizontal and vertical components of circular tracking are less mature than expected from previous studies of one-dimensional horizontal tracking. Vertical components are especially immature, particularly during high velocity tracking (approximately 20 degrees /s). The results also suggest that horizontal and vertical tracking are mutually dependent during early development. Saccades were predictive (average lag >-125 ms) from 6 months onwards.

Infants' emerging ability to represent occluded object motion

The emerging ability to represent an oscillating moving object over occlusions was studied in 7-21-week-old infants. The object moved at 0.25 Hz and was either occluded at the center of the trajectory (for 0.3 s) or at one turning point (for 0.7 s). Each trial lasted for 20 s. Both eye and head movements were measured. By using two kinds of motion, sinusoidal (varying velocity) and triangular (constant velocity), infants' ability to take velocity change into account when predicting the reappearance of the moving object was tested. Over the age period studied, performance at the central occluder progressed from almost total ignorance of what happened to consistent predictive behavior. From around 12 weeks of age, infants began to form representations of the moving object that persisted over temporary occlusions. At around 5 months of age these representations began to incorporate the dynamics of the represented motion. Strong learning effects were obtained over single trials, but there was no evidence of retention between trials. The individual differences were profound.

Directional asymmetry in smooth ocular tracking in the presence of visual background in young and adult primates

The smooth pursuit system moves the eyes in space accurately while compensating for visual inputs from the moving background and/or vestibular inputs during head movements. To understand the mechanisms underlying such interactions, we examined the influence of a stationary textured visual background on smooth pursuit tracking and compared the results in young and adult humans and monkeys. Six humans (three children, three adults) and six macaque monkeys (five young, one adult) were used. Human eye movements were recorded using infrared oculography and evoked by a sinusoidally moving target presented on a computer monitor. Scleral search coils were used for monkeys while they tracked a target presented on a tangent screen. The target moved in a sinusoidal or trapezoidal fashion with or without whole body rotation in the same plane. Two kinds of backgrounds, homogeneous and stationary textured, were used. Eye velocity gains (eye velocity/target velocity) were calculated in each condition to compare the influence of the textured background. Children showed asymmetric eye movements during vertical pursuit across the textured (but not the homogeneous) background; upward pursuit was severely impaired, and consisted mostly of catch-up saccades. In contrast, adults showed no asymmetry during pursuit across the different backgrounds. Monkeys behaved similarly; only slight effects were observed with the textured background in a mature monkey, whereas upward pursuit was severely impaired in young monkeys. In addition, VOR cancellation was severely impaired during upward eye and head movements, resulting in residual downward VOR in young monkeys. From these results, we conclude that the directional asymmetry observed in young primates may reflect a different neural organization of the vertical, particularly upward, pursuit system in the face of conflicting visual and vestibular inputs that can be associated with pursuit eye movements. Apparently, proper compensation matures later.

Eye, head and trunk control: the foundation for manual development

Mastery of reaching and manipulation relies on adequate postural control. The trunk must be balanced relative to a base of support to allow free movements of the arms and hands. Moreover, the head must be supported flexibly by the trunk so that gaze can be directed toward the target to provide a spatial frame of reference for reaching. For fine manipulation it is also crucial to avoid retinal slips which would introduce blur. Stabilizing gaze is generally accomplished through adjustments of both eye and head position. Until gaze is stabilized, it is difficult to establish a frame of reference between the target and the self. Thus, a nested hierarchy of support involving the eyes, head, and trunk forms an important foundation for manual activity.

Smooth pursuit in 1- to 4-month-old human infants

The ability of human infants < or = 4 months of age to pursue objects smoothly with their eyes was assessed by presenting small target spots moving with hold-ramp-hold trajectories at ramp velocities of 4-32 deg/sec. Infants as young as 1 month old followed such target motions with a combination of smooth-pursuit and saccadic eye movements interrupted occasionally by periods when the eyes remained stationary. The slowest targets produced variable performance, but targets moving 8-32 deg/sec produced consistent pursuit behavior, even in the youngest infants. By the fourth month, eye-movement latency decreased and smooth-pursuit gain and the percentage of smooth pursuit per trial increased for all target velocities, though these measures had not yet reached adult levels.

Development of smooth pursuit tracking in young infants

Eye and head movements were measured in a group of infants at 2, 3, and 5 months of age as they were attentively tracking an object moving at 0.2 or 0.4 Hz in sinus or triangular mode. Smooth pursuit gain increased with age, especially until 3 months. At 2-3 months, the lag of the smooth pursuit was small for the sinusoidal motion but large for the triangular one. At 5 months, smooth pursuit was leading the sinusoidal motion and the lag for the triangular one was small. Head tracking increased substantially with age and its lag was always large.

Origins and early development of perception, action, and representation

Research relevant to the origins and early development of two functionally dissociable perceptual systems is summarized. One system is concerned with the perceptual control and guidance of actions, the other with the perception and recognition of objects and events. perceptually controlled actions function in real time and are modularly organized. Infants perceive where they are and what they are doing. By contrast, research on object recognition suggests that even young infants represent some of the defining features and physical constraints that specify the identity and continuity of objects. Different factors contribute to developmental changes within the two systems; it is difficult to generalize from one response system to another; and neither perception, action, nor representation qualifies as ontogenetically privileged. All three processes develop from birth as a function of intrinsic processing constraints and experience.

The development of gaze control and predictive tracking in young infants

Eye and head tracking of an oscillating visual flow was studied in 1-, 2-, and 3-month-old infants using EOG and an opto-electronic system. A pronounced decrease in phaselag of gaze velocity was observed over this age period, from 170 to 70 msec, but gain changed only marginally. Latency of the onset of tracking decreased with age from 860 to 560 msec. During tracking, the velocity of the head showed high frequency components in the 1-6 Hz range, to which the eye movements were reciprocal and without systematic phase lag. This coordination improved with age.