Connecting the tots: Strong looking-pointing correlations in preschoolers' word learning and implications for continuity in language development

How does one assess developmental change when the measures themselves change with development? Most developmental studies of word learning use either looking (infants) or pointing (preschoolers and older). With little empirical evidence of the relationship between the two measures, developmental change is difficult to assess. This paper analyzes 914 pointing, looking children (451 female, varied ethnicities, 2.5-6.5 years, dates: 2009-2019) in 36 word- or sound-learning experiments with two-alternative test trials. Looking proportions and pointing accuracy correlated strongly (r = .7). Counter to the "looks first" hypothesis, looks were not sensitive to incipient knowledge that pointing missed: when pointing is at chance, looking proportions are also. Results suggest one possible path forward for assessing continuous developmental change. Methodological best practices are discussed.

Are Different Actions Mediated by Distinct Systems of Knowledge in Infancy?

This chapter considers why studies of infant looking and reaching often suggest different patterns of cognitive and perceptual development. In some cases, convergent results have emerged from studies of infant looking and reaching, but differences are common. The most typical results suggest less adult-like perception and cognition in studies of reaching than in studies of looking. Several reaching studies, however, do not fit this pattern, suggesting that reaching actions may be mediated by distinct systems of knowledge and information processing. Comparisons of research on other behaviors, such as crawling and walking, also suggest that infant knowledge systems vary across actions. Research on how adult size perception differs between verbal and reaching response behaviors is considered and used as a template to interpret the developmental results. Like adults, when infants prepare to engage in particular actions, they seem to shift their sensitivity to particular sources of information and to process that information in action-relevant ways. These tendencies suggest that distinct knowledge systems mediate different actions in infancy.

Infants' motor simulation of observed actions is modulated by the visibility of the actor's body

Previous research suggests that 9-month-old infants will develop a response bias in the A-not-B search paradigm after only observing an experimenter search for a hidden object on A-trials. In the current experiment, we tested whether infants would persist in making errors when only the hands-and-arms of the experimenter were visible. Three different conditions were included: (1) the experimenter was silent while hiding and finding the object, (2) the experimenter communicated with the infant via infant-directed speech, or (3) the body of the experimenter was visible during the training phase before his head and body were occluded during the test phase. Unlike previous studies, the results revealed that a significant proportion of infants searched correctly when the body of the experimenter was not visible, and only the combination of infant-directed speech and familiarization with a fully-specified body resulted in a majority of infants committing search errors. These results are interpreted as suggesting that the likelihood of infants committing search errors is dependent on their motor simulation of the experimenter's reaching. The strength of this simulation is graded by the similarity between the observed action and the motor representation.

Infants' Physical World

Investigations of infants' physical world over the past 20 years have revealed two main findings. First, even very young infants possess expectations about physical events. Second, these expectations undergo significant developments during the first year of life, as infants form event categories, such as occlusion, containment, and covering events, and identify the variables relevant for predicting outcomes in each category. A new account of infants' physical reasoning integrates these findings. Predictions from the account are examined in change-blindness and teaching experiments.

No bridge too high: infants decide whether to cross based on the probability of falling not the severity of the potential fall

Do infants, like adults, consider both the probability of falling and the severity of a potential fall when deciding whether to cross a bridge? Crawling and walking infants were encouraged to cross bridges varying in width over a small drop-off, a large drop-off, or no drop-off. Bridge width affects the probability of falling, whereas drop-off height affects the severity of the potential fall. For both crawlers and walkers, decisions about crossing bridges depended only on the probability of falling: As bridge width decreased, attempts to cross decreased, and gait modifications and exploration increased, but behaviors did not differ between small and large drop-off conditions. Similarly, decisions about descent depended on the probability of falling: Infants backed or crawled into the small drop-off, but avoided the large drop-off. With no drop-off, infants ran straight across. Results indicate that experienced crawlers and walkers accurately perceive affordances for locomotion, but they do not yet consider the severity of a potential fall when making decisions for action.

Infants use compression information to infer objects' weights: examining cognition, exploration, and prospective action in a preferential-reaching task

The present research used a preferential-reaching task to examine whether 9- and 11-month-olds (n=144) could infer the relative weights of two objects resting on a soft, compressible platform. Experiment 1 established that infants reached preferentially for the lighter of 2 boxes. In Experiments 2-4, infants saw 2 boxes identical except in weight resting on a cotton wool platform. Infants reached prospectively for the lighter box, but only when their initial exploratory activities provided critical information. At 11 months, infants succeeded as long as they first determined that the platform was compressible; at 9 months, infants succeeded only if they also explored the boxes and thus had advance knowledge that they differed in weight.

On the origin of the understanding of time, speed, and distance interrelations

We examined 18- and 24-month-old infants' sensitivity to the functional relationships between time, speed, and distance. The task included a train moving first visibly and then into a tunnel. The movement of the train was always accompanied by a train-characteristic sound signalling the travel duration. After the train concluded its travel, infants were requested to search for it in two possible locations inside the tunnel. Infants' reaching and head turn behavior indicated that 24-month-olds were sensitive to time-speed-distance interrelations, while 18-month-olds showed no such understanding. Reducing occlusion duration (by shortening the tunnel's length) revealed an increase in 18-month-olds' reaching and anticipatory head turns. Results are discussed in terms of the developmental course of the understanding of time-speed-distance interrelations and the strength of infants' representations.

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).

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.

Young infants' actions reveal their developing knowledge of support variables: converging evidence for violation-of-expectation findings

Violation-of-expectation (VOE) tasks have revealed substantial developments in young infants' knowledge about support events: by 5.5 months, infants expect an object to fall when released against but not on a surface; and by 6.5 months, infants expect an object to fall when released with 15% but not 100% of its bottom on a surface. Here we investigated whether action tasks would reveal the same developmental pattern. Consistent with VOE reports, 5.5- and 6.5-month-old infants were more likely to reach for a toy that rested on as opposed to against a surface; and 6.5- but not 5.5-month-olds were more likely to reach for a toy with 100% as opposed to 15% of its bottom on a surface. Infants at each age thus used their support knowledge to determine whether the toys were likely to be retrievable or to be attached to adjacent surfaces and hence irretrievable. These and control findings extend recent evidence that developmental patterns observed in VOE tasks also hold in action tasks, and as such provide further support for the view that VOE and action tasks tap the same physical knowledge.

Factors affecting infants' manual search for occluded objects and the genesis of object permanence

Two experiments systematically examined factors that influence infants' manual search for hidden objects (N=96). Experiment 1 used a new procedure to assess infants' search for partially versus totally occluded objects. Results showed that 8.75-month-old infants solved partial occlusions by removing the occluder and uncovering the object, but these same infants failed to use this skill on total occlusions. Experiment 2 used sound-producing objects to provide a perceptual clue to the objects' hidden location. Sound clues significantly increased the success rate on total occlusions for 10-month-olds, but not for 8.75-month-olds. An identity development account is offered for why infants succeed on partial occlusions earlier than total occlusions and why sound helps only the older infants. We propose a mechanism for how infants use object identity as a basis for developing a notion of permanence. Implications are drawn for understanding the dissociation between looking time and search assessments of object permanence.

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.

What do two-year-olds understand about hidden-object events?

Preferential-looking studies suggest that by 2 months of age, infants may have knowledge about some object properties, such as solidity. Manual search studies of toddlers examining these same concepts, however, have failed to provide evidence for the same understanding. Investigators have recently attempted to reconcile this disparity but failed to control for the visual novelty of test outcomes. The current design corrected this problem and also tested toddlers' predictions of the object's location. The task involved the same events and apparatus that have been used in manual search tasks but used looking as the dependent measure. Children looked longer when an agent opened the correct door and found no ball than when an incorrect door was opened to reveal no ball. A 2nd experiment indicated that children's preferential-looking performance did not differ from that in manual search tasks simply because additional response time had been allowed to respond. Previous comparisons of looking versus reaching tested children's postdiction response to an object in an unexpected location, but these findings indicate that toddlers can predict where the object should be.

Different Gestalt processing for different actions? Comparing object-directed reaching and looking time measures

Six experiments compared the Gestalt processing that mediates infant reaching and looking behaviors. Experiment 1 demonstrated that the positioning and timing of 8- and 9-month-olds' reaching was influenced by remembered relative motion. Experiment 2 suggested that a visible gap, without this relative motion, was not sufficient to produce these effects. Experiment 3 found that 6- and 7-month-olds required both remembered relative motion and a continuously visible gap to affect reaching; when two separate objects were placed adjacent to one another, they were treated as though they were connected. Experiments 4 and 5, using a looking time measure, identified a dissociation between looking and reaching performance. In Experiment 6, 6- and 7-month-olds' reaching was influenced when display parts differed in shape and color. In these experiments, Gestalt processing for looking was more influenced by remembered information than was Gestalt processing for reaching. For reaching, a low weighting of separation cues was also apparent.

The role of crawling and walking experience in infant spatial memory

This research explored infants' use of place learning and cue learning in a locomotor task across the transition from crawling to walking. Novice and expert crawling and walking infants were observed in a novel locomotor task-finding a hidden goal location in a large space. In Experiment 1, infants were tested with distal landmarks. Infants with fewer than 6 weeks of experience, either crawling or walking, could not find the goal location. All infants with more locomotor experience were more successful. Learning did not transfer across the transition to walking. In Experiment 2, novice and expert crawlers and walkers were tested with a direct landmark. Again, novice crawlers and walkers with fewer than 6 weeks of experience could not find the goal, whereas those with more experience could. Taken together, these findings suggest that infants' spatial learning is inextricably linked to mode of locomotion.

Demands on Finite Cognitive Capacity Cause Infants' Perseverative Errors

This research unites traditionally disparate developmental domains-cognition and locomotion-to examine the classic cognitive issue of the development of inhibition in infancy. In 2 locomotor A-not-B tasks, 13-month-old walking infants inhibited a prepotent response under low task demands (walking on flat ground), but perseverated under increased task demands (descending a staircase). Despite elimination of factors previously associated with infant perseveration, infants still perseverated in the difficult stairs condition. Increasing cognitive load by manipulating task difficulty affected infants' ability to inhibit repeated responses that were no longer appropriate. Evidence supports a cognitive capacity account of infant perseveration, in which infants' performance depends on allocation of cognitive and attentional resources.

Infants' perception of object trajectories

Filling in the gaps in what humans see is a fundamental perceptual skill, but little is known about the developmental origins of occlusion perception. Three experiments were conducted with infants between 2 and 6 months of age to investigate perception of the continuity of an object trajectory that was briefly occluded. The pattern of results across experiments provided little evidence of veridical responses to trajectory occlusion in the youngest infants, but by 6 months, perceptual completion was more robust. Four-month-olds' responses indicated that they perceived continuity under a short duration of occlusion, but when the object was out of sight for a longer interval, they appeared to perceive the trajectory as discontinuous. These results suggest that perceptual completion of a simple object trajectory (and, by logical necessity, veridical object perception) is not functional at birth but emerges across the first several months after onset of visual experience.

Lessons From Infants: 1960-2000

Our image of the infant as an organism interacting with the environment has changed dramatically in the past 40 years. A new surge of infancy research began in the 1960s and continues unabated today. The view of the infant has been transformed from that of a primarily reflexive organism to a highly competent being, exquisitely sensitive to sensory and perceptual information. Controversy still swirls around the issue of when infants acquire specific knowledge about objects and events. New work is reviewed on how infants and toddlers use knowledge to guide their behavior in challenging situations. Despite the tremendous growth of knowledge about infant development over the past 40 years, it seems that we are on the threshold of even more exciting discoveries.