Development of visually guided hand orientation in reaching

The development of an ability to use vision in adjusting the hand and the fingers to the orientation of an object to be grasped was studied in a group of 15 infants. They were 18 weeks at the first session and were seen at 4-week intervals until 34 weeks old. At each session they were presented with horizontal and vertical rods. The orientation of the hand of the infant when reaching for these rods was measured at each 60-msec interval during the last 540 msec of the approach. It was found that even at the youngest age there were signs of adjustment of the hand to the orientation of the object. However, at that age the adjustments were rather incomplete. During the months that followed there was a rapid improvement in the skill studied. The findings were in accordance with the idea that information about object orientation is accessible to the manual system when infants start reaching for objects but that the system has yet to be tuned and calibrated before functioning adequately.     

Infants’ understanding of auditory events

Infants’ reaching‐in‐the‐dark was studied in a sample of normal 7.5–11‐month‐olds to determine whether infants can use sound cues to localize and recognize the action and objects of complex events. Infants were shown an event in which a moving, sounding object rotated clockwise through the infant's reaching space in the light and dark. Infrared recorded videotapes were later coded for reaching behaviour. Results showed that infants were able to localize the object on most trials in the dark but were slower and less efficient than in the light. Infants grasped the object at first contact and contacted the object near its salient feature in the dark, suggesting recognition of the object. Further, contact time was 1.7 s less when infants grasped the object at first contact in the dark (recognition) than when they touched the object, suggesting that recognition of the object improves reaching efficiency. There were no age and gender differences. In sum, the results support the use of the reaching‐in‐the‐dark method to demonstrate auditory localization of moving sounds and to reveal infants capacity to use represented information to guide subsequent action. Copyright © 1999 John Wiley & Sons, Ltd.     

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.     

Sensitivity to binocular depth information in infants

In order to study infants' sensitivity to binocular information for depth, 11 infants, 20 to 26 weeks of age, were presented with real and stereoscopically projected virtual objects at three distances, and the infants' reaching behavior was videotaped. When the virtual object was positioned out of reach, infants tended to lean further forward and to reach less frequently than when the virtual object was positioned within reach. In addition, the proportion of reaches in which the infants patted, closed their hands, or brought their hands together was greater when the virtual object was within reach. However, no difference in the terminal location of the infants' reaches was found as a function of the virtual object's position. Examination of reaches to a near real object revealed that infants frequently did not contact the object or show appropriate hand shape or orientation. The effectiveness of the cue of retinal size and of binocular information for the depth of an object is discussed. It is concluded that 5-month-old infants are sensitive to binocular information for depth.     

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.     

Animacy and propulsion in infancy: Tracking,waving and reaching to self-propelled and induced moving objects

Infants from 16 to 20 weeks were videotaped while being presented with objects traversing a 60 cm distance. Four conditions were tested: (1) induced movement, holding the object; (2) induced movement, pushing the object; (3) self-propelled mechanical movement, object moving by an internal clockwork; (4) self-propelled biological movement, animate object moving by internal impulse. In tracking, the self-propelled but inanimate and mechanically moving object with the more straight and predictable trajectory attracted most visual attention. In arm movements, the self-propelled but relatively unpredictably moving animate object was reliably distinguished from inanimate objects. It appeared that the action system was less dependent on objects taking a straight and predictable course. Emerging with the onset of goal-directed reaches, the distinction of an internal locus of propulsion in objects was overriding the nearly exclusive response towards animacy occurring in waving. Thus, a distinction of different types of object motion could be found in infants’ developing action system.     

Object representation and predictive action in infancy

Previous research has shown that 6‐month‐old infants extrapolate object motion on linear paths when they act predictively on fully visible moving objects but not when they observe partly occluded moving objects. The present research probed whether differences in the tasks presented to infants or in the visibility of the objects account for these findings, by investigating infants’ predictive head tracking of a visible object that moves behind a small occluder. Six‐month‐old infants were presented with an object that moved repeatedly on linear or nonlinear paths, with an occluder covering the place where all the paths intersected. The first time infants viewed an object’s motion, their head movements did not anticipate either linear or nonlinear motion, but they quickly learned to anticipate linear motion on successive trials. Infants also learned to anticipate nonlinear motion, but this learning was slower and less consistent. Learning in all cases concerned the trajectory of the object, not the specific locations at which the object appeared. These findings suggest that infants form object representations that are weakly biased toward inertial motion and that are influenced by learning. The findings accord with the thesis that a single system of representation underlies both predictive action and perception of object motion, and that occlusion reduces the precision of object representations.     

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.     

Visual exploration of reaching space during left and right arm movements in 6-month-old infants

Infant's manual laterality and eye-hand coordination emerge during the second part of the first year of life with the development of reaching. Nevertheless, little is known about the potential asymmetric characteristics of this coordination. The aim of this study was to describe visuo-spatial exploration in 6-month-old infants during reaching, according to the hand used. More specifically, we examined if the use of the left or the right hand was linked to a specific type of visual exploration. Gaze direction during goal-directed reaching towards an object placed on the table was measured with a remote ASL 504 eye tracker (Bedford MA). Twelve babies aged 6 months were observed during six reaching sessions, alterning three sessions with an object on the left side of the subject and three with an object on the right side. Gaze direction and some hand variables (hand activity, hand opening and hand position from the body) were coded with The Observer software. Results showed that babies visually explore their reaching space differently according to the hand used: they look more at the object when they use their right hand and more around the object when they use their left hand; they also look more often at their left hand than at their right one. These results suggest that an asymmetric visuo-manual coordination exists as early as 6 months: vision seems to support (1) left hand during reaching for evaluate distances from object to baby by means of visual feedbacks and (2) right hand for identify what sort of object is. Results are discussed in light of manual specialization and specific hemispheric skills at this age.     

Infants generate goal-based action predictions

Predicting the actions of others is critical to smooth social interactions. Prior work suggests that both understanding and anticipation of goal-directed actions appears early in development. In this study, on-line goal prediction was tested explicitly using an adaptation of Woodward's (1998) paradigm for an eye-tracking task. Twenty 11-month-olds were familiarized to movie clips of a hand reaching to grasp one of two objects. Then object locations were swapped, and the hand made an incomplete reach between the objects. Here, infants reliably made their first look from the hand to the familiarized goal object, now in a new location. A separate control condition of 20 infants familiarized to the same movements of an unfamiliar claw revealed the opposite pattern: reliable prediction to the familiarized location, rather than the familiarized object. This study suggests that by 11 months infants actively use goal analysis to generate on-line predictions of an agent's next action.     

Visual tracking and existence constancy in 5-month-old infants

Visual fixation and cardiac deceleration for 36 infants 20–24 weeks old were recorded during three kinds of events in which objects moving on a linear trajectory were temporarily occluded by a screen: (1) a familiar object appeared on both sides of the screen; (2) a novel object appeared on both sides of the screen; and (3) a novel object appeared to change to a familiar one behind the screen. Infant attention was related to novelty and familiarity of objects and there was no evidence of behavior reflecting the expectancy that a stable object continued to exist behind the screen. These findings are in conflict with those of previous tracking studies and the discussion focuses upon explanations for this discrepancy.     

How do 8‐month‐old infants recognize causality in object motion and that in human action?1

Abstract: In Experiment 1, 8‐month‐old infants were first habituated to the event in which a moving object collided with another behind an occluder, then they were shown the two test events with no occluder: the contact event, in which the two objects actually collided, and the non‐contact event, in which the second object started to move without contact with the first. The infants looked at both events for an equal amount of time. In Experiment 2, in which the first object was a human actor, however, infants looked at the non‐contact event reliably longer than the contact event. In Experiment 3, in which both objects were human actors stood face‐to‐back, infants looked at the non‐contact event longer, whereas in Experiment 4, in which human actors faced toward each other, infants looked at both events equally. In Experiment 5, in which the first actor told the second to go, 10‐month‐old infants looked at both events for an equal amount of time. These results suggest that 8‐ and 10‐month‐old infants appreciate different causal principles between objects and humans, and that, in doing this, they may acknowledge the possibility of communication between humans.     

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.     

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.     

Remembering information related to one's self

How does memory for an incident vary depending on whether, and how, the person relates the information to himself? Trait adjectives are better remembered if they were judged in reference to oneself rather than judged for meaning or sound. Our first experiment found a similar mnemonic advantage of referring a described episode or object to some event from one's life. Pleasant events were remembered better than unpleasant ones. A second experiment found incidental memory for trait adjectives was equally enhanced by judging each directly in reference to one's self-concept or indirectly by retrieving an episode either from one's life or from one's mother's life. Contrariwise, memory was poorer when traits were judged in reference to a less familiar person. Thus, good memory depends on relating the inputs to a well-differentiated memory structure.     

Infants' use of material properties to guide their actions with differently weighted objects

Two studies with 9‐, 11‐ and 13‐month‐old infants were conducted to investigate infants' ability to use an object's material properties to guide their object‐directed actions. In study 1, 9‐ and 11‐month‐old infants played in an exploration phase with two objects made of different materials, one very heavy and the other one light and playable. Subsequently, when given the choice between both objects in a preferential reaching task, only the 11‐month‐olds' used the object's material information to remember and choose the lighter object. In study 2, 11‐ and 13‐month‐old infants underwent the same exploration phase. In the test phase, novel objects made of the same materials were offered. The 13‐ but not the 11‐month‐olds chose the objects made from the same material as the lighter object in the exploration phase. Additionally, infants' performances in the reaching task were positively correlated with their exploratory behaviour during the exploration phase. Altogether, the studies show a developmental progression in the use of an object's material information to guide infants' action. The results are discussed in respect to infants' perception of object properties and their implications for the development of physical knowledge. Copyright © 2010 John Wiley & Sons, Ltd.     

Will any doll do? 12-month-olds' reasoning about goal objects

Infants as young as 5 months of age view familiar actions such as reaching as goal-directed (Woodward, 1998), but how do they construe the goal of an actor's reach? Six experiments investigated whether 12-month-old infants represent reaching actions as directed to a particular individual object, to a narrowly defined object category (e.g., an orange dump truck), or to a more broadly defined object category (e.g., any truck, vehicle, artifact, or inanimate object). The experiments provide evidence that infants are predisposed to represent reaching actions as directed to categories of objects at least as broad as the basic level, both when the objects represent artifacts (trucks) and when they represent people (dolls). Infants do not use either narrower category information or spatiotemporal information to specify goal objects. Because spatiotemporal information is central to infants' representations of inanimate object motions and interactions, the findings are discussed in relation to the development of object knowledge and action representations.     

Infants' perception of concavity and convexity of shaded objects

The discriminative sensitivities of 30 4‐month‐old and 30 8‐month‐old infants for concave and convex objects were measured using the preferential‐looking method. Five cylinder‐like objects with different magnitudes of concave or convex shaded surfaces and outline contours were presented to the infants in pairs. The results indicated that the 4‐month‐old infants could discriminate better between object convexities than between object concavities. In contrast, the 8‐month‐old infants were able to equally discriminate between object concavities and object convexities, and their sensitivity to both object concavity/convexity was much higher than that of the 4‐month‐old infants. This difference in the sensitivity to object concavity and convexity suggested that younger and older infants might have differential abilities for cue utilization for recovering object structures.     

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.     

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.