Infants' emerging ability to represent occluded object motion

Multiple object tracking with extended occlusions

In everyday life, we often view objects through a limited aperture (e.g., soccer players on TV or cars slipping into our blind spot on a busy road), where objects often move out of view and reappear in a different place later. We modelled this situation in a series of multiple object tracking (MOT) experiments, in which we introduced a cover on the edges of the observed area and manipulated its width. This method introduced systematic occlusions, which were longer than those used in previous MOT studies. Experiment 1 (N = 50) showed that tracking under such conditions is possible, although difficult. An item-level analysis confirmed that people made more errors in targets that were covered longer and more often. In Experiment 2 (N = 50), we manipulated the tracking workload and found that the participants were less affected by the cover when the tracking load was low. In Experiment 3 (N = 50), we asked the participants to keep track of the objects' identities (multiple identity tracking [MIT]). Although MIT is subjectively more demanding, memorising identities improved performance in the most difficult cover conditions. Contrary to previous reports, we also found that even partial occlusions negatively affected tracking.

The Influence of Active and Passive Motion Experience on Infants' Visual Prediction Ability

In the present study we examined whether infants' visual prediction abilities were related to different types of motion experiences. We tested 30 6-month-old infants on a visual-spatial prediction task in which they had to visually anticipate the locational reappearance of temporarily occluded moving objects. We assigned infants to one of three experience groups: active locomotion training, passive motion experience, and a no-training control group. We tested the infants' visual prediction abilities before and after these trainings. We found improved infant predictions at a post-training test only for passively trained infants (p = .015, d = -1.033; Bonferroni corrected). Thus, we conclude that infants' visual-spatial predictions of temporally occluded moving objects was facilitated by mere movement experience, even if passive. Visual information gathered during even passive movement seemed sufficient for visual prediction.

Resolving visual motion through perceptual gaps

Perceptual gaps can be caused by objects in the foreground temporarily occluding objects in the background or by eyeblinks, which briefly but frequently interrupt visual information. Resolving visual motion across perceptual gaps is particularly challenging, as object position changes during the gap. We examine how visual motion is maintained and updated through externally driven (occlusion) and internally driven (eyeblinks) perceptual gaps. Focusing on both phenomenology and potential mechanisms such as suppression, extrapolation, and integration, we present a framework for how perceptual gaps are resolved over space and time. We finish by highlighting critical questions and directions for future work.

Capturing the objects of vision with neural networks

Human visual perception carves a scene at its physical joints, decomposing the world into objects, which are selectively attended, tracked and predicted as we engage our surroundings. Object representations emancipate perception from the sensory input, enabling us to keep in mind that which is out of sight and to use perceptual content as a basis for action and symbolic cognition. Human behavioural studies have documented how object representations emerge through grouping, amodal completion, proto-objects and object files. By contrast, deep neural network models of visual object recognition remain largely tethered to sensory input, despite achieving human-level performance at labelling objects. Here, we review related work in both fields and examine how these fields can help each other. The cognitive literature provides a starting point for the development of new experimental tasks that reveal mechanisms of human object perception and serve as benchmarks driving the development of deep neural network models that will put the object into object recognition.

Updating Expectations About Unexpected Object Motion in Infants Later Diagnosed with Autism Spectrum Disorder

In typical development, infants form predictions about future events based on incoming sensory information, which is essential for perception and goal-directed action. It has been suggested that individuals with autism spectrum disorder (ASD) make predictions differently compared to neurotypical individuals. We investigated how infants who later received an ASD diagnosis and neurotypical infants react to temporarily occluded moving objects that violate initial expectations about object motion. Our results indicate that infants regardless of clinical outcome react similarly to unexpected object motion patterns, both in terms of gaze shift latencies and pupillary responses. These findings indicate that the ability to update representations about such regularities in light of new information may not differ between typically developing infants and those with later ASD.

Developing an Understanding of Science

Young children are adept at several types of scientific reasoning, yet older children and adults have difficulty mastering formal scientific ideas and practices. Why do “little scientists” often become scientifically illiterate adults? We address this question by examining the role of intuition in learning science, both as a body of knowledge and as a method of inquiry. Intuition supports children's understanding of everyday phenomena but conflicts with their ability to learn physical and biological concepts that defy firsthand observation, such as molecules, forces, genes, and germs. Likewise, intuition supports children's causal learning but provides little guidance on how to navigate higher-order constraints on scientific induction, such as the control of variables or the coordination of theory and data. We characterize the foundations of children's intuitive understanding of the natural world, as well as the conceptual scaffolds needed to bridge these intuitions with formal science.

The positive influence of manual object exploration on predictive grasping for a moving object in 9-month-old infants

The present study examined whether infants' manual prediction ability is related to different types of their manual object exploration behavior. Thirty-two 9-month-old infants were tested in a manual prediction task, in which they were encouraged to reach for a temporarily occluded moving object. All infants also participated in a manual exploration task, in which they could freely explore five toy blocks. Infants with a high number of haptic scans in the manual exploration task showed a higher prediction rate in the manual prediction task compared to infants with a low haptic scan score. Reaction times of all infants decreased during the test blocks. However, the reaction time of infants with a high haptic scan score was faster in general. Our findings suggest that object experiences gathered by specific manual exploratory actions, such as haptic scans, are related to infants' predictive abilities when reaching and grasping for a temporarily occluded moving object.

Tracking of unpredictable moving stimuli by pigeons

Despite being observed throughout the animal kingdom, catching a moving object is a complex task and little is known about the mechanisms that underlie this behavior in non-human animals. Three experiments examined the role of prediction in capture of a moving object by pigeons. In Experiment 1, a stimulus moved in a linear trajectory, but sometimes made an unexpected 90^o turn. The sudden turn had only a modest effect on capture and error location, and the analyses suggested that the birds had adjusted their tracking to the novel motion. In Experiment 2, the role of visual input during a turn was tested by inserting disappearances (either 1.5 cm or 4.5 cm) on both the straight and turn trials. The addition of the disappearance had little effect on capture success, but delayed capture location with the larger disappearance leading to greater delay. Error analyses indicated that the birds adapted to the post-turn, post-disappearance motion. Experiment 3 tested the role of visual input when the motion disappeared behind an occluder and emerged in either a straight line or at a 90^o angle. The occluder produced a disruption in capture success but did not delay capture. Error analyses indicated that the birds did not adjust their tracking to the new motion on turn trials following occlusion. The combined results indicate that pigeons can anticipate the future position of a stimulus, and can adapt to sudden, unpredictable changes in motion but do so better after a disappearance than after an occlusion.

Developing Hierarchical Schemas and Building Schema Chains Through Practice Play Behavior

Examining the different stages of learning through play in humans during early life has been a topic of interest for various scholars. Play evolves from practice to symbolic and then later to play with rules. During practice play, infants go through a process of developing knowledge while they interact with the surrounding objects, facilitating the creation of new knowledge about objects and object related behaviors. Such knowledge is used to form schemas in which the manifestation of sensorimotor experiences is captured. Through subsequent play, certain schemas are further combined to generate chains able to achieve behaviors that require multiple steps. The chains of schemas demonstrate the formation of higher level actions in a hierarchical structure. In this work we present a schema-based play generator for artificial agents, termed Dev-PSchema. With the help of experiments in a simulated environment and with the iCub robot, we demonstrate the ability of our system to create schemas of sensorimotor experiences from playful interaction with the environment. We show the creation of schema chains consisting of a sequence of actions that allow an agent to autonomously perform complex tasks. In addition to demonstrating the ability to learn through playful behavior, we demonstrate the capability of Dev-PSchema to simulate different infants with different preferences toward novel vs. familiar objects.

The Development of Sensorimotor Intelligence in Infants

Infancy is the most dynamic part of human development. During this period, all basic sensorimotor and cognitive abilities are established. In this chapter, we will trace some of the important achievements of this development with a focus on how infants achieve predictive control of actions, i.e., how they come to coordinate their behavior with the ongoing events in the world without lagging behind. With the maturation of the brain, new possibilities that have profound effects on cognition open up. Some of them are core abilities, i.e., they function at birth or very early in development. Important examples are the structured perception of objects and surfaces and the control of arm movements. Closely after birth, infants move their arms to the vicinity of objects in front of them demonstrating that they have some control of their arms and indicating that they perceive objects as such. Another example is the rapid onset of smooth-pursuit eye movements during the second month of life and the emerging ability to predict when and where an occluded moving object will reappear. At 4months of age, out of sight is no longer of mind. The child's sensorimotor system is especially designed to facilitate the extraction of knowledge about the world including other people. In addition, the infant is endowed with motives that ensure that the innate predispositions are transformed into a system of knowledge for guiding actions predictively. By perceiving and acting on the world, infants develop their cognition and through developmental studies; we can learn more about these processes.

The relation between crawling and 9-month-old infants' visual prediction abilities in spatial object processing

We examined whether 9-month-old infants' visual prediction abilities in the context of spatial object processing are related to their crawling ability. A total of 33 9-month-olds were tested; half of them crawled for 7.6weeks on average. A new visual prediction paradigm was developed during which a three-dimensional three-object array was presented in a live setting. During familiarization, the object array rotated back and forth along the vertical axis. While the array was moving, two target objects of it were briefly occluded from view and uncovered again as the array changed its direction of motion. During the test phase, the entire array was rotated around 90° and then rotated back and forth along the horizontal axis. The targets remained at the same position or were moved to a modified placement. We recorded infants' eye movements directed at the dynamically covered and uncovered target locations and analyzed infants' prediction rates. All infants showed higher prediction rates at test and when the targets' placement was modified. Most importantly, the results demonstrated that crawlers had higher prediction rates during test trials as compared with non-crawlers. Our study supports the assumption that crawling experience might enhance 9-month-old infants' ability to correctly predict complex object movement.

10-Month-Old Infants Are Sensitive to the Time Course of Perceived Actions: Eye-Tracking and EEG Evidence

Research has shown that infants are able to track a moving target efficiently - even if it is transiently occluded from sight. This basic ability allows prediction of when and where events happen in everyday life. Yet, it is unclear whether, and how, infants internally represent the time course of ongoing movements to derive predictions. In this study, 10-month-old crawlers observed the video of a same-aged crawling baby that was transiently occluded and reappeared in either a temporally continuous or non-continuous manner (i.e., delayed by 500 ms vs. forwarded by 500 ms relative to the real-time movement). Eye movement and rhythmic neural brain activity (EEG) were measured simultaneously. Eye movement analyses showed that infants were sensitive to slight temporal shifts in movement continuation after occlusion. Furthermore, brain activity associated with sensorimotor processing differed between observation of continuous and non-continuous movements. Early sensitivity to an action's timing may hence be explained within the internal real-time simulation account of action observation. Overall, the results support the hypothesis that 10-month-old infants are well prepared for internal representation of the time course of observed movements that are within the infants' current motor repertoire.

The development of motor behavior

This article reviews research on the development of motor behavior from a developmental systems perspective. We focus on infancy when basic action systems are acquired. Posture provides a stable base for locomotion, manual actions, and facial actions. Experience facilitates improvements in motor behavior and infants accumulate immense amounts of experience with all of their basic action systems. At every point in development, perception guides motor behavior by providing feedback about the results of just prior movements and information about what to do next. Reciprocally, the development of motor behavior provides fodder for perception. More generally, motor development brings about new opportunities for acquiring knowledge about the world, and burgeoning motor skills can instigate cascades of developmental changes in perceptual, cognitive, and social domains. WIREs Cogn Sci 2017, 8:e1430. doi: 10.1002/wcs.1430 For further resources related to this article, please visit the WIREs website.

Perception of occlusion by young infants: Must the occlusion event be congruent with the occluder?

Four-month-old infants perceive continuity of an object's trajectory through occlusion, even when the occluder is illusory, and several cues are apparently needed for young infants to perceive a veridical occlusion event. In this paper we investigated the effects of dislocating the spatial relation between the occlusion events and the visible edges of the occluder. In two experiments testing 60 participants, we demonstrated that 4-month-olds do not perceive continuity of an object's trajectory across an occlusion if the deletion and accretion events are spatially displaced relative to the occluder edges (Experiment 1) or if deletion and accretion occur along a linear boundary that is incorrectly oriented relative to the occluder's edges (Experiment 2). Thus congruence of these cues is apparently important for perception of veridical occlusion. These results are discussed in relation to an account of the development of perception of occlusion and object persistence.

Effects of movement distance, duration, velocity, and type on action prediction in 12-month-olds

The goal of the present study was to test the influence of the spatial and temporal dynamics of observed manual actions on infants' action prediction. Twelve-month-old infants were presented with reach-and-transport actions performed by a human agent. Movement distance, duration, and - resulting from the two - movement velocity were systematically varied. Action prediction was measured via the latency of gaze arrival at target in relation to agent's hand. The results showed a general effect of all parameters on the infants' perception of goal-directed actions: Infants were more likely to predict the action goal the longer the movement distance was, the longer the movement duration was, and the slower the movement velocity was. In addition, they were more likely to predict the goal of a reaching than a transport action. The present findings extent previous findings by showing that infants are not only sensitive to differences in distances, durations, and velocities at early age but that these factors have a strong impact on the prediction of the goal of observed actions.

Development of Visual Motion Perception for Prospective Control: Brain and Behavioral Studies in Infants

During infancy, smart perceptual mechanisms develop allowing infants to judge time-space motion dynamics more efficiently with age and locomotor experience. This emerging capacity may be vital to enable preparedness for upcoming events and to be able to navigate in a changing environment. Little is known about brain changes that support the development of prospective control and about processes, such as preterm birth, that may compromise it. As a function of perception of visual motion, this paper will describe behavioral and brain studies with young infants investigating the development of visual perception for prospective control. By means of the three visual motion paradigms of occlusion, looming, and optic flow, our research shows the importance of including behavioral data when studying the neural correlates of prospective control.

Development of internal models and predictive abilities for visual tracking during childhood

The prediction of the consequences of our own actions through internal models is an essential component of motor control. Previous studies showed improvement of anticipatory behaviors with age for grasping, drawing, and postural control. Since these actions require visual and proprioceptive feedback, these improvements might reflect both the development of internal models and the feedback control. In contrast, visual tracking of a temporarily invisible target gives specific markers of prediction and internal models for eye movements. Therefore, we recorded eye movements in 50 children (aged 5-19 yr) and in 10 adults, who were asked to pursue a visual target that is temporarily blanked. Results show that the youngest children (5-7 yr) have a general oculomotor behavior in this task, qualitatively similar to the one observed in adults. However, the overall performance of older subjects in terms of accuracy at target reappearance and variability in their behavior was much better than the youngest children. This late maturation of predictive mechanisms with age was reflected into the development of the accuracy of the internal models governing the synergy between the saccadic and pursuit systems with age. Altogether, we hypothesize that the maturation of the interaction between smooth pursuit and saccades that relies on internal models of the eye and target displacement is related to the continuous maturation of the cerebellum.

Extrapolation and direct matching mediate anticipation in infancy

Why are infants able to anticipate occlusion events and other people's actions but not the movement of self-propelled objects? This study investigated infant and adult anticipatory gaze shifts during observation of self-propelled objects and human goal-directed actions. Six-month-old infants anticipated self-propelled balls but not human actions. This demonstrates that different processes mediate the ability to anticipate human actions (direct matching) versus self-propelled objects (extrapolation).

Differential contributions of development and learning to infants' knowledge of object continuity and discontinuity

Sixty infants divided evenly between 5 and 7 months of age were tested for their knowledge of object continuity versus discontinuity with a predictive tracking task. The stimulus event consisted of a moving ball that was briefly occluded for 20 trials. Both age groups predictively tracked the ball when it disappeared and reappeared via occlusion, but not when it disappeared and reappeared via implosion. Infants displayed high levels of predictive tracking from the first trial in the occlusion condition, and showed significant improvement across trials in the implosion condition. These results suggest that infants possess embodied knowledge to support differential tracking of continuously and discontinuously moving objects, but this tracking can be modified by visual experience.

Actions Seen through Babies' Eyes: A Dissociation between Looking Time and Predictive Gaze

In this study, we explored the relation of two different measures used to investigate infants' expectations about goal-directed actions. In previous studies, expectations about action outcomes have been either measured after the action has been terminated, that is post-hoc (e.g., via looking time) or during the action is being performed, that is online (e.g., via predictive gaze). Here, we directly compared both types of measures. Experiment 1 demonstrated a dissociation between looking time and predictive gaze for 9-month-olds. Looking time reflected identity-related expectations whereas predictive gaze did not. If at all, predictive gaze reflected location-related expectations. Experiment 2, including a wider age range, showed that the two measures remain dissociated over the first 3 years of life. It is only after the third birthday that the dissociation turns into an association, with both measures then reflecting identity-related expectations. We discuss these findings in terms of an early dissociation between two mechanisms for action expectation. We speculate that while post-hoc measures primarily tap ventral mechanisms for processing identity-related information (at least at a younger age), online measures primarily tap dorsal mechanisms for processing location-related information.

Sex differences during visual scanning of occlusion events in infants

A growing number of sex differences in infancy have been reported. One task on which they have been observed reliably is the event-mapping task. In event mapping, infants view an occlusion event involving 1 or 2 objects, the occluder is removed, and then infants see 1 object. Typically, boys are more likely than girls to detect an inconsistency between a 2-object occlusion event and a 1-object display. The current research investigated underlying reasons for this sex difference. Three eye-tracking experiments were conducted with infants at 9 and 4 months (mean age). Infants saw a ball-box or ball-ball occlusion event followed by a 1-ball display; visual scanning of the occlusion event and the 1-ball display was recorded. Older boys were more likely than older girls to visually track the objects through occlusion and more likely to detect an inconsistency between the ball-box event and the 1-ball display. In addition, tracking objects through occlusion was related to infants' scanning of the 1-ball display. Both younger boys and girls failed to track the objects through occlusion and to detect an inconsistency between the ball-box event and the 1-ball display. These results suggest that infants' capacity to track objects through occlusion facilitates extraction of the structure of the initial event (i.e., the number of distinct objects involved) that infants can map onto the final display and that sex differences in the capacity emerge between 4 and 9 months. Possible explanations for how the structure of an occlusion event is extracted and mapped are considered.

Predictive coding strategies for developmental neurorobotics

In recent years, predictive coding strategies have been proposed as a possible means by which the brain might make sense of the truly overwhelming amount of sensory data available to the brain at any given moment of time. Instead of the raw data, the brain is hypothesized to guide its actions by assigning causal beliefs to the observed error between what it expects to happen and what actually happens. In this paper, we present a variety of developmental neurorobotics experiments in which minimalist prediction error-based encoding strategies are utilize to elucidate the emergence of infant-like behavior in humanoid robotic platforms. Our approaches will be first naively Piagian, then move onto more Vygotskian ideas. More specifically, we will investigate how simple forms of infant learning, such as motor sequence generation, object permanence, and imitation learning may arise if minimizing prediction errors are used as objective functions.

The effects of auditory information on 4-month-old infants' perception of trajectory continuity

Young infants perceive an object's trajectory as continuous across occlusion provided the temporal or spatial gap in perception is small. In 3 experiments involving 72 participants the authors investigated the effects of different forms of auditory information on 4-month-olds' perception of trajectory continuity. Provision of dynamic auditory information about the object's trajectory enhanced perception of trajectory continuity. However, a smaller positive effect was also obtained when the sound was continuous but provided no information about the object's location. Finally, providing discontinuous auditory information or auditory information that was dislocated relative to vision had negative effects on trajectory perception. These results are discussed relative to the intersensory redundancy hypothesis and emphasize the need to take an intersensory approach to infant perception.

The effects of auditory information on 4-month-old infants' perception of trajectory continuity

Young infants perceive an object's trajectory as continuous across occlusion provided the temporal or spatial gap in perception is small. In 3 experiments involving 72 participants the authors investigated the effects of different forms of auditory information on 4-month-olds' perception of trajectory continuity. Provision of dynamic auditory information about the object's trajectory enhanced perception of trajectory continuity. However, a smaller positive effect was also obtained when the sound was continuous but provided no information about the object's location. Finally, providing discontinuous auditory information or auditory information that was dislocated relative to vision had negative effects on trajectory perception. These results are discussed relative to the intersensory redundancy hypothesis and emphasize the need to take an intersensory approach to infant perception.

Sound support: intermodal information facilitates infants' perception of an occluded trajectory

In a visual occlusion task, 4-month-olds were given a dynamic sound cue (following the trajectory of an object), or a static cue (sound remained stationary). Infants' oculomotor anticipations were greater in the Dynamic condition, suggesting that representations of visual occlusion were supported by auditory information.

Action production influences 12-month-old infants' attention to others' actions

Recent work implicates a link between action control systems and action understanding. In this study, we investigated the role of the motor system in the development of visual anticipation of others' actions. Twelve-month-olds engaged in behavioral and observation tasks. Containment activity, infants' spontaneous engagement in producing containment actions; and gaze latency, how quickly they shifted gaze to the goal object of another's containment actions, were measured. Findings revealed a positive relationship: infants who received the behavior task first evidenced a strong correlation between their own actions and their subsequent gaze latency of another's actions. Learning over the course of trials was not evident. These findings demonstrate a direct influence of the motor system on online visual attention to others' actions early in development.

Are visual features of a looming or receding object processed in a capacity-free manner?

Numerous experiments have examined whether moving stimuli capture spatial attention but none have sought to determine whether visual features of looming and receding objects are extracted in a capacity-free manner. The current experiment (N=28) used the task-choice procedure originated by Besner and Care (2003) to examine this possibility. Stimuli were presented in 3D space by manipulating retinal disparity. Results indicate that features of an object are extracted in a capacity-free manner for both looming and receding objects for participants who consciously perceive motion but not for participants who do not consciously perceive motion. These results suggest that the cognitive system is biased to process potentially animate objects, perhaps because of the evolutionary advantage this cognitive ability may provide.

Infants' representations of three-dimensional occluded objects

Infants' ability to represent objects has received significant attention from the developmental research community. With the advent of eye-tracking technology, detailed analysis of infants' looking patterns during object occlusion have revealed much about the nature of infants' representations. The current study continues this research by analyzing infants' looking patterns in a novel manner and by comparing infants' looking at a simple display in which a single three-dimensional (3D) object moves along a continuous trajectory to a more complex display in which two 3D objects undergo trajectories that are interrupted behind an occluder. Six-month-old infants saw an occlusion sequence in which a ball moved along a linear path, disappeared behind a rectangular screen, and then a ball (ball-ball event) or a box (ball-box event) emerged at the other edge. An eye-tracking system recorded infants' eye-movements during the event sequence. Results from examination of infants' attention to the occluder indicate that during the occlusion interval infants looked longer to the side of the occluder behind which the moving occluded object was located, shifting gaze from one side of the occluder to the other as the object(s) moved behind the screen. Furthermore, when events included two objects, infants attended to the spatiotemporal coordinates of the objects longer than when a single object was involved. These results provide clear evidence that infants' visual tracking is different in response to a one-object display than to a two-object display. Furthermore, this finding suggests that infants may require more focused attention to the hidden position of objects in more complex multiple-object displays and provides additional evidence that infants represent the spatial location of moving occluded objects.

Anticipatory reaching of seven- to eleven-month-old infants in occlusion situations

The present study examined 7- to 11-month-old infants' anticipatory and reactive reaching for temporarily occluded objects. Infants were presented with laterally approaching objects that moved at different velocities (10, 20, and 40 cm/s) in different occlusion situations (no-, 20 cm-, and 40 cm-occlusion), resulting in occlusion durations ranging between 0 and 4s. Results show that except for object velocity and occlusion distance, occlusion duration was a critical constraint for infants' reaching behaviors. We found that the older infants reached more often, but that an increase in occlusion duration resulted in a decline in reaching frequency that was similar across age groups. Anticipatory reaching declined with increasing occlusion duration, but the adverse effects for longer occlusion durations diminished with age. It is concluded that with increasing age infants are able to retain and use information to guide reaching movements over longer periods of non-visibility, providing support for the graded representation hypothesis (Jonsson & von Hofsten, 2003) and the two-visual systems model (Milner & Goodale, 1995).

Action, the foundation for cognitive development

It is argued that action constitutes the foundation for cognitive development. Action is a principal component of all aspects of cognitive development including social understanding. It reflects the motives of the child, the problems to be solved, the goals to be attained, and the constraints and possibilities of the child's body and sensory-motor system. Actions are directed into the future and their control is based on knowledge of what is going to happen next. The child's sensory-motor system is especially designed to facilitate the extraction of this knowledge. In addition, the infant is endowed with motives that ensure that these innate predispositions are transformed into a system of knowledge for guiding actions. By acting on the world, infants develop their cognition.

Beyond the search barrier: A new task for assessing object individuation in young infants

Object individuation, the capacity to track the identity of objects when perceptual contact is lost and then regained, is fundamental to human cognition. A great deal of research using the violation-of-expectation method has been conducted to investigate the development of object individuation in infancy. At the same time, there is a growing need for converging methods of study. Reported here are data obtained with from a newly developed search task that can be used with infants as young as 5 months of age. The results suggest that this method is a sensitive measure of object individuation in young infants and demonstrate the advantages of using converging methods of study.

Occlusion is hard: Comparing predictive reaching for visible and hidden objects in infants and adults

Infants can anticipate the future location of a moving object and execute a predictive reach to intercept the object. When a moving object is temporarily hidden by darkness or occlusion, 6-month-old infants' reaching is perturbed but performance on darkness trials is significantly better than occlusion trials. How does this reaching behavior change over development? Experiment 1 tested predictive reaching of 6- and 9-month-old infants. While there was an increase in the overall number of reaches with increasing age, there were significantly fewer predictive reaches during the occlusion compared to visible trials and no age-related changes in this pattern. The decrease in performance found in Experiment 1 is likely to apply not only to the object representations formed by infants but also those formed by adults. In Experiment 2 we tested adults with a similar reaching task. Like infants, the adults were most accurate when the target was continuously visible and performance in darkness trials was significantly better than occlusion trials, providing evidence that there is something specific about occlusion that makes it more difficult than merely lack of visibility. Together, these findings suggest that infants' and adults' capacities to represent objects have similar signatures throughout development.

Learning and memory facilitate predictive tracking in 4-month-olds

We investigated 4-month-olds' oculomotor anticipations when viewing occlusion stimuli consisting of a small target that moved back and forth repetitively while the center of its trajectory was occluded by a rectangular screen. We examined performance under five conditions. In the baseline condition, infants produced few predictive relative to reactive eye movements. In the full training condition, anticipations were increased in frequency following prior exposure to a target moving along a fully visible trajectory. The delay condition tested the effects of training after a 30-min interval elapsed between training and test, resulting in a return to baseline performance. However, the training effect was reinstated in the reminder condition following another brief exposure to the training stimulus prior to test. Finally, in the brief training condition, we found that the brief exposure alone was insufficient to induce the training effect. Results are interpreted in the context of learning from short-term experience and long-term memory.

Development of object concepts in macaque monkeys

One of the most interesting questions in cognitive development is how we acquire and mentally represent knowledge about objects. We investigated the development of object concepts in macaque monkeys. Monkeys viewed trajectory occlusion movies in which a ball followed a linear path that was occluded for some portion of the display while their point of gaze was recorded with a corneal-reflection eye tracker. We analyzed the pattern of eye movements as an indicator of object representation. A majority of eye movements of adult monkeys were anticipatory, implying a functional internal object representation that guided oculomotor behavior. The youngest monkeys lacked this strong internal representation of objects. Longitudinal testing showed that this ability develops over time providing compelling evidence that object concepts develop similarly in monkeys and humans. Therefore, the macaque monkey provides an animal model with which to examine neural mechanisms underlying the development of object representations.

Predictive tracking over occlusions by 4-month-old infants

Two experiments investigated how 16-20-week-old infants visually tracked an object that oscillated on a horizontal trajectory with a centrally placed occluder. To determine the principles underlying infants' tendency to shift gaze to the exiting side before the object arrives, occluder width, oscillation frequency, and motion amplitude were manipulated resulting in occlusion durations between 0.20 and 1.66 s. Through these manipulations, we were able to distinguish between several possible modes of behavior underlying 'predictive' actions at occluders. Four such modes were tested. First, if passage-of-time determines when saccades are made, the tendency to shift gaze over the occluder is expected to be a function of time since disappearance. Second, if visual salience of the exiting occluder edge determines when saccades are made, occluder width would determine the pre-reappearance gaze shifts but not oscillation frequency, amplitude, or velocity. Third, if memory of the duration of the previous occlusion determines when the subjects shift gaze over the occluder, it is expected that the gaze will shift after the same latency at the next occlusion irrespective of whether occlusion duration is changed or not. Finally, if infants base their pre-reappearance gaze shifts on their ability to represent object motion (cognitive mode), it is expected that the latency of the gaze shifts over the occluder is scaled to occlusion duration. Eye and head movements as well as object motion were measured at 240 Hz. In 49% of the passages, the infants shifted gaze to the opposite side of the occluder before the object arrived there. The tendency to make such gaze shifts could not be explained by the passage of time since disappearance. Neither could it be fully explained in terms of visual information present during occlusion, i.e. occluder width. On the contrary, it was found that the latency of the pre-reappearance gaze shifts was determined by the time of object reappearance and that it was a function of all three factors manipulated. The results suggest that object velocity is represented during occlusion and that infants track the object behind the occluder in their 'mind's eye'.

Conditions for young infants? failure to perceive trajectory continuity

When viewing an event in which an object moves behind an occluder on part of its trajectory, 4-month-old infants perceive the trajectory as continuous only when time or distance out of sight is short. Little is known, however, about the conditions under which young infants perceive trajectories to be discontinuous. In the present studies we focus first on infants' perception of trajectories that change during a period of occlusion. Four-month-olds perceive discontinuity in trajectories that change in height or orientation while behind an occluder, and this is true even when a change in direction could be due to an invisible bouncing collision with a surface. Further experiments reveal that infants do not perceive diagonal linear trajectories as continuous across an occlusion unless the occluding and revealing edges are orthogonal to the path of movement. Implications for theories of perceptual and cognitive development are discussed.

Phenomenal permanence and the development of predictive tracking in infancy

The perceived spatiotemporal continuity of objects depends on the way they appear and disappear as they move in the spatial layout. This study investigated whether infants' predictive tracking of a briefly occluded object is sensitive to the manner by which the object disappears and reappears. Five-, 7-, and 9-month-old infants were shown a ball rolling across a visual scene and briefly disappearing via kinetic occlusion, instantaneous disappearance, implosion, or virtual occlusion. Three different measures converged to show that predictive tracking increased with age and that infants were most likely to anticipate the reappearance of the ball following kinetic occlusion. These results suggest that infants' knowledge of the permanence and nonpermanence of objects is embodied in their predictive tracking.

Anticipatory models in gaze control: a developmental model

Infants gradually learn to predict the motion of moving targets and change from a strategy that mainly depends on saccades to one that depends on anticipatory control of smooth pursuit. A model is described that combines three types of mechanisms for gaze control that develops in a way similar to infants. Initially, gaze control is purely reactive, but as the anticipatory models become more accurate, the gain of the pursuit will increase and lead to a larger fraction of smooth eye movements. Finally, a third system learns to predict changes in target motion, which will lead to fast retuning of the parameters in the anticipatory model.