The ontogeny of infant bimanual reaching during the first year

Handedness and pattern of coordination during bimanual reaching were assessed separately for six groups of infants, 7 to 12 months old. Infants reached bimanually for a transparent toy-filled box. On some presentations of the box a low barrier was placed in the path of either the right or left hand, while on other presentations there was no barrier. The youngest and two oldest groups of infants were more likely than the other age groups to perform simultaneous bimanual reaches with no barrier present, but when a barrier was present the 11-month-olds were most likely to continue to perform simultaneous reaches. This suggests that while infants as young as 7 months perform simultaneous reaches, the organization of these reaches may be different than for older infants. Hand-use preference contributed significantly to selection of a lead hand in non-simultaneous bimanual reaching. The 8-month group, which had the highest proportion of infants with a hand preference, was the only group likely to hit the barrier when it was placed on the nonpreferred side. Hand preference may, thus, bias the use of information about what the environment affords for action.     

Young infants reach correctly in A-not-B tasks: on the development of stability and perseveration

This paper examines the development of perseverative reaching in the A-not-B task. We describe two recent models that view perseveration as a sign of developmental progress toward stability. In Experiment 1, we test the novel prediction from both models that very young infants should not perseverate in the A-not-B task whereas older infants should. We tracked infants' behavior monthly on the A-not-B task and found that infants reached correctly at 5 months, and only perseverated at 7 and 8 months of age. Experiment 2 provides further evidence on the role of motor development in the emergence of perseveration by exploring the connection between perseveration and detailed changes in reach kinematics in two infants across the first year. These data together suggest that perseveration is a sign of developmental achievement on the path to stable and flexible behavior.     

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.     

The impact of object size and rigidity on infant reaching

Although the changes in kinematics of infant reaching have been studied, few researchers have investigated the improvement of reaching regarding objects of distinct physical properties. The aim of this longitudinal study was to verify the impact of object size and rigidity on the development of reaching in 4-6-month-old infants. Four infants were observed with a motion capture system during trials with four objects of distinct sizes and rigidity. A total of 188 reaches were analyzed by using the 3D movement reconstruction. Our results showed that reaching frequency, mean velocity, and straightness index increased with age. The number of movement units decreased with age and increased for small objects. Rigidity was not shown to affect reaching trajectories. These findings suggest that infants are capable of perceiving the more relevant object properties, thus using their available motor capabilities to modify the essential variables so that they can reach the target more accurately.     

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.     

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.     

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).     

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.     

Proximal and distal adjustments of reaching behavior in preterm infants

The authors aimed to investigate proximal and distal adjustments of reaching behavior and grasping in 5-, 6-, and 7-month-old preterm infants. Nine low-risk preterm and 10 full-term infants participated. Both groups showed the predominance of unimanual reaching, an age-related increase in the frequency of vertical-oriented and open hand movement, and also an increase in successful grasping from 6 to 7 months. The frequency of open hand was higher in the preterm group at 6 months. Intrinsic restrictions imposed by prematurity did not seem to have impaired reaching performance of preterm infants throughout the months of age.     

Influence of Different Sitting Positions on Healthy Infants' Reaching Movements

The authors analyze the influence of different sitting positions (ring and flexion) on the reaching performance (spatiotemporal variables) of full-term infants 6 and 7 months old. In addition, they correlated level of trunk control, measured by the Segmental Assessment of Trunk Control, with performance during reaching. The different sitting positions only influenced the reaching movements of 6-month-old infants, who showed the best performance in the ring position. However, this influence was observed only for the trunk displacement, deceleration time, movement units, straightness index and mean velocity. In contrast, there was no influence of positions on 7-month-old infants’ reaching performance. Regarding the correlations, it was observed that infants with more level of trunk control showed a better performance when reaching, regardless of position and the age assessed.     

Development of infant reaching behaviors: Kinematic changes in touching and hitting

This longitudinal study investigated the development of reaching in typical infants, from age 4 to 8 months, and described the pattern of hand kinematics underlying changes in the characteristics of infants’ actions while reaching for a target. Thirteen infants were followed biweekly. Two reaching behaviors emerged during the infants’ free interactions with the target, touching and hitting. Changes over time were documented for the number of movement units, straightness index, distance, peak velocity and time to peak velocity of the hand for touches and hits. We observed increases in the numbers of touches and hits and changes in hand kinematics over time; the distance traveled by the hand was greater for hitting compared to touching. These kinematic changes were specific to the movement patterns that infants adopted to reach to the target.     

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).     

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.     

Contingent auditory feedback of arm movement facilitates reaching behavior in infancy

The purpose of this study was to investigate the influence of contingent auditory feedback on the development of infant reaching. Eleven full-term infants were observed biweekly from the age of 10 weeks to 16 weeks, and their arm kinematics were recorded. Auditory feedback that was contingent on arm kinematics was provided in the form of: (a) the mother's voice; and (b) musical tones. Results showed that providing auditory feedback (mother's voice or musical tones): (i) increased the amplitude of exploratory arm movements before the onset of reaching; and (ii) increased the number of reaches at the onset of reaching. These results show that infants are able to use contingent auditory feedback to explore the relevant possibilities for action that are subsequently shaped into goal-directed movements.     

SES affects infant cognitive flexibility

Cognitive flexibility requires processing multiple sources of information and flexible adaptation of behavioral responses. Poverty negatively impacts cognitive control in young children, but its effects on infants are not well-understood. This study investigated longitudinally the development of cognitive flexibility in low-income infants. Thirty-two infants (15 low-SES, 17 high-SES) were tested at 6, 9, and 12 months of age. Cognitive flexibility was measured with a perseverative reaching task, where infants were taught to reach to one location and then asked to switch to a second location. High-SES infants replicated the typical developmental trajectory, reaching randomly at 6 months, perseverating at 9 months, and reaching correctly at 12 months. In contrast, the low-SES infants showed a delayed pattern, reaching correctly at 6 months, randomly at 9 months, and perseverating at 12 months. Links between cognitive flexibility and frontal cortex development are explored as a potential mechanism.     

Infants’ ability to track and reach for temporarily occluded objects

Six‐month‐old infants were presented with a moving object that temporarily became invisible. The object moved on a horizontal path and was made invisible for either 400, 800 or 1,200 ms before being within reach. Two kinds of events were used to make the object invisible: blackout of the room lights and occlusion behind a screen. First, infants saw 6 trials of the fully visible motion, then 12 trials of a temporarily invisible motion and finally 6 trials of the fully visible motion again. Each infant was presented with only one of the 6 experimental conditions. The results show that reaching is much more severely affected by a period of temporary non‐visibility than tracking. The effects of the two modes of non‐visibility were rather different. In general, blackout deteriorated tracking and made the gaze lag at reappearance. It inhibited reaching but this effect attenuated with experience. Longer periods of blackout deteriorated tracking and reaching more. Compared to blackout, occlusion had both a facilitating and an inhibiting effect on infants’ actions. Tracking had less tendency to lag but reaching showed more severe inhibition. The results are discussed in terms of graded representations. Furthermore, it is argued that an occluder facilitates tracking by providing information of where the moving object becomes visible again and it inhibits reaching by interfering with the representation of the object behind the occluder.     

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.     

Infants’ sensitivity to the depth cue of shading

Five- and 7-month-old infants were tested for sensitivity to the depth cue of shading. Infants were presented with two displays: a surface in which a convexity and a concavity were molded and a photograph in which shading specified a convexity and a concavity. Each display was presented under both monocular and binocular viewing conditions. Reaching was observed as the dependent measure. Infants in both age groups reached preferentially for the actual convexity in both the monocular and binocular viewing conditions. In the monocular photograph condition, the 7-month-olds reached preferentially for the apparent convexity specified by shading, indicating that they perceived it to be an actual convexity. These infants showed no significant reaching preference in the binocular photograph condition. This finding rules out interpretations of the infants’ reaching not based on perceived depth. The results therefore suggest that the 7-month-olds perceived depth from shading. The 5-month-olds showed no significant reaching preferences when viewing the photograph; thus, they showed no evidence of depth perception from shading. These findings are consistent with the results of a number of studies that have investigated infants’ sensitivity to pictorial depth cues. Together, these studies suggest that the ability to perceive depth from pictorial cues may first develop between 5 and 7 months of age.     

The role of locomotor posture and experience on handedness and footedness in infancy

This research examined the development of handedness and footedness in infancy. We measured footedness by documenting the limb infants used to "lead-out" as they crawled or walked down a path several times. We measured handedness by documenting the hand infants used to reach for a goal at the end of each trial. Study 1 showed that locomotor skill affects limb lateralization preferences and that most 13-month-old infants demonstrated a side preference for reaching and leading out "in the moment." Study 2 longitudinally examined the developmental trajectories of handedness and footedness as they related to locomotor posture and experience. The findings suggest high variability in the developmental trajectory of footedness, with frequent fluctuation between side preferences. The developmental trajectory of handedness was more stable over the transition between locomotor milestones. The transition between crawling and walking decreased the proportion of infants demonstrating side preferences for leading out and the onset of walking decreased the proportion of infants demonstrating side preferences for reaching. These findings demonstrate the importance of making behavioral observations at multiple time scales to understand underlying developmental trajectories, specifically the stability or instability of the motor system associated with the acquisition of new motor abilities.     

How infants use perceptual information to guide action

When infants catch a rolling ball by intercepting its trajectory, the action is prospectively controlled to take account of the object's speed, direction and path. We complicated this task in two ways: by occluding a portion of the ball's path with a screen, and by sometimes placing a barrier that blocked the ball's path behind the screen. In two experiments we manipulated visual information about the barrier and the ball's trajectory to see how this would aid 9‐month‐olds’ performance. Anticipatory reaching was possible but difficult with a partially occluded trajectory; actually catching the ball was aided by full view of the trajectory although timing of reach onset was not affected. Full sight of the barrier and trajectory through a transparent screen prevented inappropriate reaching, whereas sight of the barrier alone through a ‘window’ in an opaque screen did not. We interpreted these results as evidence for decreased performance as cognitive load increased with the loss of visual information. In contrast to anticipatory reaching behavior, search for the ball after it disappeared behind the screen was facilitated by the opaque window condition, confirming previous studies that found superior search with opaque versus transparent screens.