Object perception and object-directed reaching in infancy

Five-month-old infants were presented with a small object, a larger object, and a background surface arranged in depth so that all were within reaching distance. Patterns of reaching for this display were observed, while spatial and kinetic properties of the display were varied. When the infants reached for the display, they did not reach primarily for the surfaces that were nearer, smaller, or presented in motion. The infants reached, instead, for groups of surfaces that formed a unit that was spatially connected and/or that moved as a whole relative to its surroundings. Infants reached for the nearer of two objects as a distinct unit when the objects were separated in depth or when one object moved relative to the other. They reached for the two objects as a single unit when the objects were adjacent or when they moved together. The reaching patterns provided evidence that the infants organized each display into the kind of units that adults call objects: manipulable units with internal coherence and external boundaries. Infants, like adults, perceived objects by detecting both the spatial arrangements and the relative movements of surfaces in the three-dimensional layout.     

Predictive reaching for moving objects by human infants

To what degree do infants use a predictive strategy when reaching for moving objects? This question was studied longitudinally in five infants from 18 to 36 weeks of age. The aiming of 356 reaches were analyzed by a technique that took into consideration the three-dimensional properties of the reaches. Each reach was divided into ballistic steps and the aiming of each step was calculated and compared with an optimal value. It was found that the infants studied had an ability to reach for fast moving objects in a predictive way. Further, the results show that the predictive ability is remarkably good in the lowest age groups which suggests that it is, at least partly, prewired. What develops seems mainly to be the mobility aspects of reaching which makes for more economical and flexible reaching. Older infants reach successfully for the fast moving object also with a nonpredictive chasing strategy.     

Visual feedback of hand trajectory and the development of infant prehension

The purpose of this longitudinal infant study was to investigate the influence of visual information of the hand trajectory in the development of reaching movements in prehension. Ten infants were observed biweekly from the age of 10 weeks to 28 weeks and 1 yr. The reach kinematics were analyzed at age of reach onset, 6 mo and 1 yr of age. The results showed that infants reached for objects earlier when the visual feedback of the hand trajectory and the object were available. However, visual feedback of the hand trajectory did not change the movement speed and smoothness of the reach component at 6 mo and 1 yr of age. Infants reached for the larger object earlier and with higher velocity than for the smaller object. Visual feedback of the hand facilitates the age of reaching onset, but when the reaching movements become sufficiently stable, infants perform equally well with or without visual trajectory feedback of the hand.     

Age Changes in Interlimb Coupling and the Development of Bimanual Coordination

Changes in interlimb coupling, and their role in the development of bimanual coordination, were studied longitudinally in 6- to 12-month-old infants (N = 6). Infants were observed while they were reaching for simple objects of 2 different sizes. Their use of a uni-versus bimanual strategy for reaching as well as the coupling of their bimanual movements were compared; progress in bimanual coordination of complementary movements was evaluated on 8 different bimanual tasks. The bimanual tasks involved an asymmetrical cooperation between the 2 hands. Although spatiotemporal coupling of bimanual reaching movements did not decrease during the age period studied, infants around 7 months of age used their 2 hands infrequently for reaching. Occurrences of bimanual reaching were particularly low at the session preceding the first bimanual success at a bimanual task. This suggests that the temporal coincidence between greater independence of the 2 hands and progress in bimanual coordination of complementary movements acts in 2 directions: Infants may be more at ease when using their 2 hands in differentiated patterns as the hands move less in synchrony, but, in turn, they may be less likely to move their hands in synchrony as the anticipate mirror manipulations of the object less. The frequency of bimanual reaches increased toward the end of the 1st year. This might have been caused by an increase in the repertoire of bimanual asymmetrical object manipulations and by the fact that the development of bimanual coordination allows infants to manipulate objects with complementary movements even after a bimanual approach toward the object.     

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.     

Linked proximal and distal changes in the reaching behavior of 5- to 12-month-old human infants grasping objects of different sizes

This study evaluates age-related proximal and distal changes in reaching organization for objects of different sizes. To this end, eight objects ranging from 2 to 9 cm diam. were presented to 23 infants ages 5 to 12 months. Proximal control was determined by the relative frequencies of bimanual reaching for large and small objects. Distal control was assessed by hand opening and orientation with respect to an object, and by the proportion of the object being included within hand opening at touch. Five-month-old infants tended to reach bimanually regardless of object size. Starting at 7 to 8 months, infants tended to reach for large objects bimanually more often than for small ones. Only at 11 to 12 months did reaching closely reflect the object’s diameter. The frequency of thumb-index finger angle opening during the approach phase also increased after 7 to 8 months of age, as well as the adjustment of the angle to the object diameter and the proportion of the object within hand opening at touch. Proximal and distal changes appeared coupled at 5 to 6 months, when the few subjects showing evidence of some proximal adjustments to object size were also those who exhibited some distal adjustments. After they started to appear, however, proximal and distal adjustments seemed to be independent, as revealed by the lack of correlation of proximal and distal changes between 7 and 12 months.     

The development of reaching and looking preferences in infants to objects of different sizes.

Reaching and looking preferences and movement kinematics were recorded in 5-15-month-old infants, who were divided into 3 age groups. Infants were presented with pairs of cylinders of 3 different diameters: small (1-cm diameter), medium (2.5-cm diameter), and large (6-cm diameter). Whereas infants between 5 and 12 months of age showed a preference for looking first at the large object, a significant preference for reaching to smaller (graspable) objects was observed in 81/2-12-month-old infants. Kinematic measures suggest that the onset of object-oriented action requires a slowing down of the reach and an extended "homing-in" phase. The divergent looking and reaching preferences in infants at different ages may reflect a dissociation during development of visual processing streams subserving object-related action from those related to visual orienting.     

Motor training at 3 months affects object exploration 12 months later

The development of new motor skills alters how infants interact with objects and people. Consequently, it has been suggested that motor skills may initiate a cascade of events influencing subsequent development. However, only correlational evidence for this assumption has been obtained thus far. The current study addressed this question experimentally by systematically varying reaching experiences in 40 three‐month‐old infants who were not reaching on their own yet and examining their object engagement in a longitudinal follow‐up assessment 12 months later. Results revealed increased object exploration and attention focusing skills in 15‐month‐old infants who experienced active reaching at 3 months of age compared to untrained infants or infants who only passively experienced reaching. Further, grasping activity after – but not before – reaching training predicted infants’ object exploration 12 months later. These findings provide evidence for the long‐term effects of reaching experiences and illustrate the cascading effects initiated by early motor skills.     

Spatio-temporal parameters in infant's reaching movements are influenced by body orientation

Many studies have demonstrated that the seated position is more effective in promoting reaching movements when compared with supine. The aim of this longitudinal study was to verify the effect of seated and supine positions on spatio-temporal parameters of reaching in 4-6-month-old infants. Four infants were observed during reaching trials in both positions. A total of 235 reaches were analyzed by using the 3D movement reconstruction. Our results showed that frequency of reaching and straightness index increased over age. Significant differences between the positions were observed at 4 months, when the frequency increased and the duration and deceleration time decreased in the seated position. There were no significant differences at 5 and 6 months. These findings suggest that young infants are able to change kinematical parameters of reaching to adapt themselves to intrinsic and extrinsic constraints (i.e. age and position).     

Change of spatial field effects in 16- to 20-week-old infants

Infants from 16 to 20 weeks were presented with objects moving across a 60-cm distance. Tracking increased between 16 and 18 weeks, reaching increased at 18 weeks, and arm lifts (swipes) showed no age change. A right spatial field bias in tracking disappeared gradually. Swipes occurred most often in front of the object, when it was moving in the center field, presumably as reactions due to spatial proximity. Reaching occurred in the peripheral spatial fields in the younger infants, but in the older infants most often in the center spatial field. Moreover, reaching occurred generally more often toward the left spatial field and predicted the emergence of tracking the left spatial field. Thus, it appeared that a bias in reaching corrected a bias in tracking. Similar effects of limb movements, especially when reaching, were found in the successful treatment of visual neglect patients in neuropsychological research.     

Encoding the goal of an object-directed but uncompleted reaching action in 6- and 9-month-old infants

Infants start to interpret completed human actions as goal-directed in the second half of the first year of life. In a series of three studies, the understanding of a goal-directed but uncompleted action was investigated in 6- and 9-month-old infants using a preferential looking paradigm. Infants saw the video of an actor's reaching movement towards one of two objects. This reaching movement was only presented until the hand passed the midpoint between the starting position and the position of the target object. Subsequently, two final states of the reaching movement were presented simultaneously. In the plausible final state, the hand grasped the object to which the reaching movement was geared; in the implausible final state, the hand grasped the other object. In Studies 1 and 3, infants watched the actor from an allocentric perspective, and in Studies 2 and 3 from an egocentric perspective. Results indicate a discrimination of the two final states if the scene was presented from an allocentric perspective: both 6- and 9-month-olds looked longer at the implausible final state. This was not the case if infants saw the action from an egocentric perspective. The presented findings show that using this paradigm, 6-month-olds are already able to infer the goal of an uncompleted action without seeing the achievement of the goal itself. However, they encoded the goal of the reaching action only when it was presented from an allocentric perspective but not from an egocentric perspective.     

Rapid word learning in 13- and 17-month-olds in a naturalistic two-word procedure: looking versus reaching measures

This study investigated infants’ rapid learning of two novel words using a preferential looking measure compared with a preferential reaching measure. In Experiment 1, 21 13-month-olds and 20 17-month-olds were given 12 novel label exposures (6 per trial) for each of two novel objects. Next, in the label comprehension tests, infants were shown both objects and were asked, “Where’s the [label]?” (looking preference) and then told, “Put the [label] in the basket” (reaching preference). Only the 13-month-olds showed rapid word learning on the looking measure; neither age group showed rapid word learning on the reaching measure. In Experiment 2, the procedure was repeated 24 h later with 10 participants per age group from Experiment 1. After a further 12 labels per object, both age groups now showed robust evidence of rapid word learning, but again only on the looking measure. This is the earliest looking-based evidence of rapid word learning in infants in a well-controlled (i.e., two-word) procedure; our failure to replicate previous reports of rapid word learning in 13-month-olds with a preferential reaching measure may be due to our use of more rigorous controls for object preferences. The superior performance of the younger infants on the looking measure in Experiment 1 was not straightforwardly predicted by existing theoretical accounts of word learning.     

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 4 s. 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).     

Reaching skills of infants born very preterm predict neurodevelopment at 2.5 years

The purpose was to investigate associations between quality of reaching for moving objects at 8 months corrected age and neurodevelopment at 2.5 years in children born very preterm (gestational age (GA), 24–31 weeks). Thirtysix infants were assessed while reaching for moving objects. The movements were recorded by a 3D motion capture system. Reaching parameters included aiming, relative length of the reach, number of movement units, proportion of bimanual coupled reaches and number of hits. Neurodevelopment was assessed at 2.5 years by the Bayley Scales of Infant Development III. There were strong associations between infant reaching kinematics and neurodevelopment of cognition and language but the patterns differed: in children born extremely preterm (GA < 28 weeks), planning and control of reaching was strongly related to outcome, while in children born very preterm (GA 28–31 weeks) number of hits and bimanual strategies were of greater relevance. In conclusion, for extremely preterm infants, basic problems on how motion information is incorporated with action planning prevail, while in very preterm infants the coordination of bimanual reaches is more at the focus. We conclude that the results reflect GA related differences in neural vulnerability and that early motor coordination deficits have a cascading effect on neurodevelopment.     

Do Early Nouns Refer to Kinds or Distinct Shapes? Evidence From 10-Month-Old Infants

ABSTRACT— What is the nature of early words? Specifically, do infants expect words for objects to refer to kinds or to distinct shapes? The current study investigated this question by testing whether 10-month-olds expect internal object properties to be predicted by linguistic labels. A looking-time method was employed. Infants were familiarized with pairs of identical or different objects that made identical or different sounds. During test, before the sounds were demonstrated, paired objects were labeled with one repeated count-noun label or two distinct labels. Results showed that infants expected objects labeled with distinct labels to make different sounds and objects labeled with repeated labels to make identical sounds, regardless of the objects' appearance. These findings indicate that the 10-month-olds' expectations about internal properties of objects were driven by labeling and provide evidence that even at the beginning of word learning, infants expect distinct labels to refer to different kinds.     

Head and eye movements affect object processing in 4‐month‐old infants more than an artificial orientation cue

This study investigates the effects of attention‐guiding stimuli on 4‐month‐old infants' object processing. In the human head condition, infants saw a person turning her head and eye gaze towards or away from objects. When presented with the objects again, infants showed increased attention in terms of longer looking time measured by eye tracking and an increased Nc amplitude measured by event‐related potentials (ERP) for the previously uncued objects versus the cued objects. This suggests that the uncued objects were previously processed less effectively and appeared more novel to the infants. In a second condition, a car instead of a human head turned towards or away from objects. Eye‐tracking results did not reveal any significant difference in infants' looking time. ERPs indicated only a marginally significant effect in late slow‐wave activity associated with memory encoding for the uncued objects. We conclude that human head orientation and gaze direction affect infants' object‐directed attention, whereas movement and orientation of a car have only limited influence on infants' object processing.     

Patterns of 4-month-old infant responses to hidden silent and sounding people and objects

Responses of 4-month-old infants to hidden people and objects were investigated with equated task demands. Twenty-one 4-month-old infants were administered a combined task, in which they were shown a sounding stimulus that continued to sound after hiding, an auditory task, in which sound was the only source of information about the position of the object in space, and a vision task, in which a silent stimulus was shown to the infants prior to hiding. Five infant behaviours were coded: reaching, gazing, body movements, vocalizations and smiles. The infants reached significantly more for hidden objects than for people, to whom they vocalized instead. They further smiled, and moved their bodies more towards their invisible mother than to the other stimuli. Thus infants responded differentially to people and objects whether the stimuli were soundless (so that there was no cue to their presence) or not. This suggested that infants appreciated (a) that an object had been hidden; (b) this object was either animate or inanimate; and (c) different procedures were appropriate for the retrieval of, or for interacting with animate and inanimate objects. Discussion centres on the underlying representational system that allows for such appreciation.     

Infants’ perception of depth from cast shadows

Five- and 7-month-old infants viewed displays in which cast shadows provided information that two objects were at different distances. The 7-month-olds reached preferentially for the apparently nearer object under monocular-viewing conditions but exhibited no reaching preference under binocularviewing conditions. These results indicate that 7-month-old infants perceive depth on the basis of cast shadows. The 5-month-olds did not reach preferentially for the apparently nearer object and, therefore, exhibited no evidence of sensitivity to cast shadows as depth information. In a second experiment, 5-month-olds reached preferentially for the nearer of two objects that were similar to those used in the first experiment but were positioned at different distances from the infant. This result indicated that 5-month-olds have the motor skills and motivation necessary to exhibit a reaching preference under the conditions of this study. The results are consistent with the hypothesis that depth perception based on cast shadows first appears between 5 and 7 months of age.     

Infants' perception of depth from cast shadows

Five- and 7-month-old infants viewed displays in which cast shadows provided information that two objects were at different distances. The 7-month-olds reached preferentially for the apparently nearer object under monocular-viewing conditions but exhibited no reaching preference under binocular-viewing conditions. These results indicate that 7-month-old infants perceive depth on the basis of cast shadows. The 5-month-olds did not reach preferentially for the apparently nearer object and, therefore, exhibited no evidence of sensitivity to cast shadows as depth information. In a second experiment, 5-month-olds reached preferentially for the nearer of two objects that were similar to those used in the first experiment but were positioned at different distances from the infant. This result indicated that 5-month-olds have the motor skills and motivation necessary to exhibit a reaching preference under the conditions of this study. The results are consistent with the hypothesis that depth perception based on cast shadows first appears between 5 and 7 months of age.     

The emergence of kind-based object individuation in infancy

Four experiments investigated whether 12-month-old infants use perceptual property information in a complex object individuation task, using the violation-of-expectancy looking time method (Xu, 2002; Xu & Carey, 1996). Infants were shown two objects with different properties emerge and return behind an occluder, one at a time. The occluder was then removed, revealing either two objects (expected outcome, if property differences support individuation) or one object (unexpected outcome). In Experiments 1-3, infants failed to use color, size, or a combination of color, size, and pattern differences to establish a representation of two distinct objects behind an occluder. In Experiment 4, infants succeeded in using cross-basic-level-kind shape differences to establish a representation of two objects but failed to do so using within-basic-level-kind shape differences. Control conditions found that the methods were sensitive. Infants succeeded when provided unambiguous spatiotemporal information for two objects, and they encoded the property differences during these experiments. These findings suggest that by 12 months, different properties play different roles in a complex object individuation task. Certain salient shape differences enter into the computation of numerical distinctness of objects before other property differences such as color or size. Since shape differences are often correlated with object kind differences, these results converge with others in the literature that suggest that by the end of the first year of life, infants' representational systems begin to distinguish kinds and properties.