Consequences of Eye Color,Positioning, and Head Movement for Eye‐Tracking Data Quality in Infant Research

Eye tracking has become a valuable tool for investigating infant looking behavior over the last decades. However, where eye‐tracking methodology and achieving high data quality have received a much attention for adult participants, it is unclear how these results generalize to infant research. This is particularly important as infants behave different from adults in front of the eye tracker. In this study, we investigated whether eye physiology, positioning, and infant behavior affect measures of eye‐tracking data quality: accuracy, precision, and data loss. We report that accuracy and precision are lower, and more data loss occurs for infants with bluish eye color compared to infants with brownish eye color. Moreover, accuracy was lower for infants positioned in a high chair or in the parents' lap compared to infants positioned in a baby seat. Finally, precision decreased and data loss increased as a function of time. We highlight the importance of data quality when comparing multiple groups, as differences in data quality can affect eye‐tracking measures. In addition, we investigate how two different measures to quantify infant movement influence eye‐tracker data quality. These findings might help researchers with data collection and help manufacturers develop better eye‐tracking systems for infants.     

Gaze Behaviors of Preterm and Full‐Term Infants in Nonsocial and Social Contexts of Increasing Dynamics: Visual Recognition,Attention Regulation,and Gaze Synchrony

Although research has demonstrated poor visual skills in premature infants, few studies assessed infants’ gaze behaviors across several domains of functioning in a single study. Thirty premature and 30 full‐term 3‐month‐old infants were tested in three social and nonsocial tasks of increasing complexity and their gaze behavior was micro‐coded. In a one‐trial version of the visual recognition paradigm, where novel stimuli were paired with familiar stimuli, preterm infants showed longer first looks to novel stimuli. In the behavior response paradigm, which presented infants with 17 stimuli of increasing complexity in a predetermined “on‐off” sequence, premature infants tended to look away from toys more during presentation. Finally, during mother–infant face‐to‐face interaction, the most dynamic interpersonal context, preterm infants and their mothers displayed short, frequent episodes of gaze synchrony, and lag‐sequential analysis indicated that both mother and infant broke moments of mutual gaze within 2 sec of its initiation. The propotion of look away during the behavior response paradigm was related to lower gaze synchrony and more gaze breaks during mother–infant interactions. Results are discussed in terms of the unique and adaptive gaze patterns typical of low‐risk premature infants.     

Robustness and Precision: How Data Quality May Influence Key Dependent Variables in Infant Eye‐Tracker Analyses

In recent years, eye‐tracking has become a popular method for drawing conclusions about infant cognition. Relatively little attention has been paid, however, to methodological issues associated with infant eye‐tracking. Here, we consider the possibility that systematic differences in the quality of raw eye‐tracking data obtained from different populations and individuals might create the impression of differences in gaze behavior, without this actually being the case. First, we show that lower quality eye‐tracking data are obtained from populations who are younger and populations who are more fidgety and that data quality declines during the testing session. Second, we assess how these differences in data quality might influence key dependent variables in eye‐tracking analyses. We show that lower precision data can appear to suggest a reduced likelihood to look at the eyes in a face relative to the mouth. We also show that less robust tracking may manifest as slower reaction time latencies (e.g., time to first fixation). Finally, we show that less robust data can manifest as shorter first look/visit duration. We argue that data quality should be reported in all analyses of infant eye‐tracking data and/or that steps should be taken to control for data quality before performing final analyses.     

Maternal input and infants’ response to infant‐directed speech

Caregivers typically use an exaggerated speech register known as infant‐directed speech (IDS) in communication with infants. Infants prefer IDS over adult‐directed speech (ADS) and IDS is functionally relevant in infant‐directed communication. We examined interactions among maternal IDS quality, infants’ preference for IDS over ADS, and the functional relevance of IDS at 6 and 13 months. While 6‐month‐olds showed a preference for IDS over ADS, 13‐month‐olds did not. Differences in gaze following behavior triggered by speech register (IDS vs. ADS) were found in both age groups. The degree of infants’ preference for IDS (relative to ADS) was linked to the quality of maternal IDS infants were exposed to. No such relationship was found between gaze following behavior and maternal IDS quality and infants’ IDS preference. The results speak to a dynamic interaction between infants’ preference for different kinds of social signals and the social cues available to them.     

Free Viewing Gaze Behavior in Infants and Adults

The current study investigated age differences in free viewing gaze behavior. Adults and 6‐, 9‐, 12‐, and 24‐month‐old infants watched a 60‐sec Sesame Street video clip while their eye movements were recorded. Adults displayed high intersubject consistency in eye movements; they tended to fixate the same places at the same. Infants showed weaker consistency between observers and intersubject consistency increased with age. Across age groups, the influence of both bottom‐up features (fixating visually salient areas) and top‐down features (looking at faces) increased. Moreover, individual differences in fixating bottom‐up and top‐down features predicted whether infants’ eye movements were consistent with those of adults, even when controlling for age. However, this relation was moderated by the number of faces available in the scene, suggesting that the development of adult‐like viewing involves learning when to prioritize looking at bottom‐up and top‐down features.     

Disentangling the Effects of an Adult Model's Eye Gaze and Head Orientation on Young Infants' Processing of a Previously Attended Object

In order to disentangle the effects of an adult model's eye gaze and head orientation on infants' processing of objects attended to by the adult, we presented 4‐month‐olds with faces that either (1) shifted eye gaze toward or away from an object while the head stayed stationary or (2) that turned their head while maintaining gaze directed straight ahead. Infants' responses to the previously attended and unattended objects were measured using eye‐tracking and event‐related potentials. In both conditions, infants responded to objects that were not cued by the adult's head or eye gaze shift with more visual attention and an increased negative central (Nc) component relative to cued objects. This suggests that cued objects had been encoded more effectively, whereas uncued objects required further processing. We conclude that eye gaze and head orientation act independently as cues to direct infants' attention and object processing. Both head orientation and eye gaze, when presented in motion, even override the effects of incongruent stationary information from the other kind of cue.     

Preference for Dynamic Human Images and Gaze‐Following Abilities in Preterm Infants at 6 and 12 Months of Age: An Eye‐Tracking Study

Preterm children are reported to be at higher risk of social communication problems such as autism spectrum disorder compared with full‐term infants. Although previous studies have suggested that preference for social stimuli in infancy is a possible indicator of later social communication development, little is known about this relation in preterm infants. We examined the gaze behavior of low‐risk preterm and full‐term infants at 6 and 12 months' corrected ages using two types of eye‐tracking tasks, which measured 1) preference for social stimuli by biological motion and human geometric preference and 2) ability to follow another's gaze direction. We found that preterm (compared with full‐term) infants at both 6 and 12 months of age spent less time looking toward dynamic human images, followed another's gaze less frequently, and looked for a shorter time at an object cued by another. Moreover, we found a positive correlation between looking time toward dynamic human images and frequency of gaze following at 12 months of age in full‐term, but not preterm, infants. We discuss the relation between the atypical patterns of gaze behavior in preterm infants and their higher risk of later social communication problems.     

Anticipatory Eye Movements Reveal Infants' Auditory and Visual Categories

We introduce a new paradigm for the assessment of auditory and visual categories in 6‐month‐old infants using a 2‐alternative anticipatory eye‐movement response. Infants were trained by 2 different methods to anticipate the location of a visual reinforcer at 1 of 2 spatial locations (right or left) based on the identity of 2 cuing stimuli. After a training phase, infants were presented with a series of generalization trials in which novel (untrained) stimuli served as the cue to the anticipatory eye movement. Four experiments illustrated that infants can learn the 2‐choice discriminative response during training. Infants also showed anticipatory eye movements to novel stimuli, indicating sensitivity to variations along a variety of stimulus dimensions (e.g., color, shape, orientation, spatial frequency, pitch, and duration). In addition, the paradigm can be used to assess categorization in individual infants, thereby revealing the stimulus dimensions to which infants naturally attend.     

How Manual Object Exploration is Associated with 7‐ to 8‐Month‐Old Infants’ Visual Prediction Abilities in Spatial Object Processing

The present experiment examined whether infants’ visual prediction performance of the appearance of objects moving in space is related to their manual object exploration ability. Fifty‐five 7‐ to 8‐month‐old infants were tested. A visual object prediction paradigm was developed during which a three‐dimensional object was presented in a live eye‐tracking setting. During familiarization, the object rotated back and forth along the vertical axis. While the object was moving, two target parts of it were briefly occluded from view and uncovered again as the object changed its direction of motion. In the test phase, the entire object was rotated around 90° and now rotated along the horizontal axis. We recorded infants’ eye movements directed at the target locations and analyzed the prediction rates. All of the infants also participated in a manual object exploration task, in which they freely explored five toy blocks. Infants with a higher level of object exploration skill had higher prediction rates during test trials as compared to infants with less proficient object exploratory actions. The results support the interpretation that advanced manual object exploration experience is associated with infants’ advanced visual prediction ability of the appearance of objects moving in space.     

The Quality of Spontaneous Movements of Preterm Infants: Associations with the Quality of Mother–Infant Interaction

The assessment of the quality of infants’ spontaneous movements is a diagnostic tool for the young nervous system. We examined whether it relates to the quality of the interactions between infants born preterm and their mothers. Thirty‐nine healthy infants born preterm (M_{age in weeks} = 14.59, SD = 2.21; 38.46% female) and their mothers participated in the study. Infants’ quality of spontaneous movements was assessed using the General Movement Assessment according to Prechtl (Prechtl, Early Human Development 1990, 23, 151). A new measurement was employed to evaluate the following aspects of the mother–infant interaction: maternal sensitivity in the motor modality (i.e., when touching, picking up, holding, and putting down the infant), maternal sensitivity in the modalities of vocalization and eye contact, and infants’ positive engagement. Several aspects of infants’ quality of movements were associated with maternal sensitivity in the motor modality and infants’ positive engagement, but not with maternal sensitivity in the modalities of vocalization and eye contact. These findings suggest that the quality of infants’ spontaneous movements may explain some of the variability in the interactions between infants born preterm and their mothers. The results also highlight the importance of differentiating between the modalities of mothers’ behavior when assessing their sensitivity. Implications for research and practice with families of preterm infants are discussed.     

Looking Forward: Comment on Morgante,Zolfaghari, and Johnson

Morgante et al. (in press) find inconsistencies in the time reporting of a Tobii T60XL eye tracker. Their study raises important questions about the use of the Tobii T‐series in particular, and various software and hardware in general, in different infant eye tracking paradigms. It leaves open the question of the source of the inconsistencies. Here, observations from a Tobii eye tracker are presented to elucidate possible sources of timing inconsistencies, including those found by Morgante et al. The ramifications of the reported timing inconsistencies are related to various infant paradigms. The focus is on the level of concern a researcher should have if any eye tracker displays these timing characteristics, and what corrective measures may be taken. While posing no problems for some paradigms, timing inconsistencies are potentially problematic (but correctable) when assessing event‐related looking behavior. Observed timing contraindicates use in fast gaze‐contingent displays (<100 ms). General suggestions are made regarding timing in eye‐tracked data collection.     

Developmental Changes in Visual Scanning of Dynamic Faces and Abstract Stimuli in Infants: A Longitudinal Study

The characteristics of scanning patterns between the ages of 6 and 26 weeks were investigated through repeated assessments of 10 infants. Eye movements were recorded using a corneal‐reflection system while the infants looked at 2 dynamic stimuli: the naturally moving face of their mother and an abstract stimulus. Results indicated that the way infants scanned these stimuli stabilized only after 18 weeks, which is slightly later than the ages reported in the literature on infants' scanning of static stimuli. This effect was especially prominent for the abstract stimulus. From the 14‐week session on, infants adapted their scanning behavior to the stimulus characteristics. When scanning the video of their mother's face, infants directed their gaze at the mouth and eye region most often. Even at the youngest age, there was no indication of an edge effect.     

Cortical Indexes of Saccade Planning in Infants

This article briefly reviews the development of cortical involvement in saccadic eye movement in young infants. A distinction between reflexive and voluntary saccadic eye movements is made, and developmental changes in the neural systems controlling these eye movements are discussed. Cortical indexes of saccade planning in adults have been measured using scalp‐recorded, event‐related potential (ERP). The ERP may be useful in distinguishing reflexive and voluntary saccadic eye movements in infants. In the remainder of this Thematic Collection, 3 studies are introduced that used ERP measures to infer saccade planning in young infants, and 2 short articles comment on these studies.     

Automated Corneal‐Reflection Eye Tracking in Infancy: Methodological Developments and Applications to Cognition

Since the mid‐1800s, experimental psychologists have been using eye movements and gaze direction to make inferences about perception and cognition in adults (Müller, 1826, cited in Boring, 1942). In the past 175 years, these oculomotor measures have been refined (see Kowler, 1990) and used to address similar questions in infants (see Aslin, 1985, 1987; Branson, 1982; Haith, 1980; Maurer, 1975). The general rationale for relying on these visual behaviors is that where one is looking is closely tied to what one is seeing. This is not to deny the fact that we can detect visual stimuli in the peripheral visual field, but rather that there is a bias to attend to and process information primarily when it is located in the central portion of the retina. Thus, although the direction of gaze is not perfectly correlated with the uptake of visual information (e.g., as in a blank stare or a covert shift of attention), there is a strong presumption that the direction of gaze can provide important information about visual stimuli even in newborn infants (Haith, 1966; Salapatek, 1968; Salapatek & Kessen, 1966).     

Development of Tactile Responses in Human Preterm and Full‐Term Infants From 30 to 40 Weeks Postconceptional Age

Maturation of tactile sensitivity prior to term was examined in 36 preterm and 13 full‐term infants using a fixed‐trial, habituation procedure. Each infant was presented with a series of 8 habituation (arm stroke), 2 novel (arm lift), and 2 recovery (arm stroke) stimulus trials while heart rate and body movements were recorded. Maturation was observed with a gradual increase in the magnitude of the stimulus‐elicited cardiac acceleration and cardiac‐movement coupling from 30 to 40 weeks postconceptional age. The majority of infants displayed habituation—an excitatory response (heart rate acceleration and body movement)—to the initial presentation of a tactile stimulus, response decline with repeated stimulations, and renewed response to a novel stimulus. A substantial number of infants (40%) failed to respond initially to the tactile stimulus, increased responding over several stimulus presentations, and failed to discriminate the presentation of a novel stimulus. We speculate that these differences in response patterns observed over all ages represent individual difference in the perception of stimulus intensity.     

Fine‐Grained Analysis of Motionese: Eye Gaze,Object Exchanges,and Action Units in Infant‐Versus Adult‐Directed Action

Mothers modify their actions when demonstrating objects to infants versus adults. Such modifications have been called infant‐directed action (IDA) or motionese (Brand, Baldwin, & Ashburn, 2002). We investigated the IDA features of interactiveness and simplification by quantifying eye gaze, object exchanges, and action units enacted between exchanges in 42 mothers' demonstrations of novel objects to infants (6–8 months or 11–13 months) or adults. We found more eye gaze, more object exchanges, and fewer action types per turn in demonstrations to infants relative to adults. Unlike prior research using global measurements, we detected differences in behavior directed at infants of different ages: Shorter, more frequent gazes and more exchanges characterized demonstrations to older versus younger infants. These findings indicate the fruitfulness of fine‐grained analysis of IDA, and further clarify how adults may support infants' processing of human motion.     

Peripheral Stimulus Localization by Infants of Moving Stimuli on Complex Backgrounds

This study examined the effect of attention in young infants on the saccadic localization of dynamic peripheral stimuli presented on complex and interesting backgrounds. Infants at 14, 20, and 26 weeks of age were presented with scenes from a Sesame Street movie until fixation on a moving character occurred and then presented with a second segment in the scene in which the character movement occurred in a new location. Localization of the moving character in the new location was faster when the infant was engaged in attention than when inattentive, for scenes in which the character moved from one location to another, or scenes in which the character stopped moving and characters in new locations began moving. However, localization of the character was slower during attention when the first character disappeared and a different character appeared in a new location. We also found a decrease in the linear component of the main sequence in the saccade characteristics over the three testing ages, and attention affected the main sequence for infants at the two oldest ages. These results partially replicate prior findings showing that attention to a focal stimulus affects localization of peripheral stimuli, but suggest that the nature of the stimuli being localized modifies the role of attention in affecting eye movements to peripheral stimuli.     

Infants' Visual Recognition of Pincer Grip Emerges Between 9 and 12 Months of Age

The development of the ability to recognize the whole human body shape has long been investigated in infants, while less is known about their ability to recognize the shape of single body parts, and in particular their biomechanical constraints. This study aimed to explore whether 9‐ and 12‐month‐old infants have knowledge of a hand‐grasping movement (i.e., pincer grip), being able to recognize violations of the hand's anatomical constraints during the observation of that movement. Using a preferential looking paradigm, we showed that 12‐month‐olds discriminate between biomechanically possible and impossible pincer grips, preferring the former over the latter (Experiment 1). This capacity begins to emerge by 9 months of age, modulated by infants' own sensorimotor experience with pincer grip (Experiment 2). Our findings indicate that the ability to visually discriminate between pincer grasps differing in their biomechanical properties develops between 9 and 12 months of age, and that experience with self‐produced hand movements might help infants in building a representation of the hand that encompasses knowledge of the physical constraints of this body part.     

Using Object Knowledge in Visual Tracking and Reaching

Nine‐month‐old infants were presented with an engaging and challenging task of visually tracking and reaching for a rolling ball that disappeared and reappeared from behind an occluder. On some trials, the infant observed the experimenter place a barrier on the ball's track; the barrier remained partially visible above the occluder throughout the remainder of the trial. When the task involved only predictive tracking, infants' anticipatory gaze shifts were faster when no barrier was present. When the task involved both tracking and reaching, there were more reaches when no barrier was present. If the infant reached, the timing and extension of the reach and the accompanying gaze shift did not differ with regard to the barrier. Because catching the ball was quite difficult for these infants, task demands interfered with the integration of visual information and visuospatial reasoning about the barrier with the reaching action.     

Your Eyes Say “No,” But Your Heart Says “Yes”: Behavioral and Psychophysiological Indices in Infant Quantitative Processing

Behavioral indices (e.g., infant looking) are predominantly used in studies of infant cognition, but psychophysiological measures have been increasingly integrated into common infant paradigms. The current study reports a result in which behavioral measures and physiological measures were both incorporated in a task designed to study infant number discrimination. Seven‐month‐old infants were habituated to several sets of stimuli varying in object type, but of a constant numerical value (either two or three items). Although looking time to each of the test trials revealed no differences, differences in heart rate defined measures of attention revealed infants’ ability to discriminate number. These findings imply that the inclusion of indices other than behavioral measures should become commonplace in studies of infant cognition.